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The evolution of our understanding of human development over the last 10 years

Ali h. brivanlou.

1 Stem Cell Biology and Molecular Embryology Laboratory, The Rockefeller University, New York, NY USA

Norbert Gleicher

2 The Center for Human Reproduction, New York, NY USA

3 The Foundation for Reproductive Medicine, New York, NY USA

4 Department of Obstetrics and Gynecology, Medical University of Vienna, Vienna, Austria

As it fulfills an irresistible need to understand our own origins, research on human development occupies a unique niche in scientific and medical research. In this Comment, we explore the progress in our understanding of human development over the past 10 years. The focus is on basic research, clinical applications, and ethical considerations.

What basic research has taught us about human development

Over the last decade, progress in understanding our own development was mostly driven by the emergence and combination of remarkable new technologies. New molecular biology tools such as single-cell RNA-sequencing (sc-RNA-seq) unveiled the earliest genetic signature of the three cell lineages of the human blastocyst and allowed for the discovery of human-specific signatures 1 – 3 . CRISPR/Cas9 genome editing has offered further access to in vitro functional studies in human blastocysts 4 . However, as we discuss below, an ethical line was crossed when a group claimed that genetically modified human embryos had been transferred, leading to births 5 when neither public opinion nor a consensus within the scientific community had been reached regarding whether crossing the germline in in vitro fertilization (IVF) was safe and ethically acceptable.

On the embryology side, the development of an in vitro attachment platform for human blastocysts offered a first glance into post-implantation events up to 12 days 1 , 3 , 5 , 6 . This paved the way for several important discoveries, including the observation that the human embryo can self-organize to generate embryonic and extraembryonic germ layers, yolk sac, and amniotic cavities in the absence of maternal influences 5 , 6 ; and the presence of a transient embryonic tissue of trophectodermal lineage, adjacent to the yolk sac, therefore named, yolk-sac trophectoderm ( ysTE ) 5 . The presence of these seemingly human-specific populations was independently confirmed by sc-RNA-seq 1 .

The marriage of stem cell biology with bioengineering gave birth to the field of synthetic embryology 7 – 13 . This technology uses human embryonic stem cells (hESCs) cultured on geometrically confined micropatterned substrates to generate 2D in vitro models of human conceptuses, such as models of the gastrula ( gastruloids ) 7 – 13 , or parts of the embryo, such as cerebroids and neuruloids 14 . Thousands of nearly identical self-organizing human embryonic structures allow for standardization and reproducibility, which cannot be achieved in standard organoid structures 15 . Cells within these structures can be tracked and quantified in real time with sub-cellular resolution, using sophisticated quantification code, including artificial intelligence 14 .

Human gastruloids induce formation of the primitive streak and have enabled the deciphering of the molecular network underlying gastrulation—the most crucial moment of our lives 7 – 13 . 3D models of human epiblasts can spontaneously break axial symmetry, thus providing an assay for the elucidation of molecular events underlying the emergence of antero–posterior polarity 11 , 16 . A highly homogenous population of self-organizing 3D models of amniotic ectoderm-like cells can be obtained by combining microfluidic and microculture approaches 17 .

Finally, the development of interspecies chimeras provided the most stringent in vivo validation of human embryo models 9 , 10 , 18 . Unimaginable in human models, inter-species chimeras have become the next best choice to test whether hESC behavior in self-organizing gastruloids , as observed on microchips, would also occur in an embryonic environment 10 , 18 , 19 . Human/bird chimeras generated from transplanting human gastruloids into early chick embryos in ovo unexpectedly proved more efficient than previous methods 9 , 19 . They allowed for the observation of an entire self-organizing embryonic axis in bird eggs 9 . As birds are closer to dinosaurs than to humans, this high rate of success with these chimeras further suggested that these early patterning events must be highly conserved.

Translational clinical applications that arose from basic research

The past 10 years bore witness to significant clinical progress in reproductive medicine, often translated from basic research. Successful human uterus transplantation and the subsequent birth of healthy offspring was, for example, only achieved after years of meticulous laboratory work in animals 10 . Significant improvements in cryopreservation technology for human eggs and ovarian tissue were also preceded by research in model systems 10 , 20 . Practical clinical applications have been developed for women in need of cancer treatment that are toxic to ovaries. In these cases, oocytes and/or ovarian tissue can be cryopreserved for later use in fertility treatments once the patient is cured of her cancer 21 . This ever-evolving technology has already proven to result in live births, and has also become an integral part of routine infertility treatments with IVF, giving rise to the brand-new concept of fertility extension through egg-freezing.

Diagnostic technologies to assess retrieved eggs and preimplantation-stage embryos in the IVF process have been disappointing. For example, tracking extended embryo culture to blastocyst-stage with time-lapse imaging failed to improve embryo selection 22 . That chromosomal-abnormal embryos increase with maternal (but not paternal) age has been interpreted to mean that chromosomal abnormalities were a principal cause for lower implantation chances and higher miscarriage risks among older women. This assumption led to the rapidly growing utilization of chromosomal testing of human embryos prior to embryo transfer in a procedure recently renamed preimplantation genetic testing for aneuploidy (PGT-A) 23 . The hypothesis behind PGT-A is to exclude chromosomal-abnormal embryos from the transfer, thereby improving implantation potentials of remaining euploid embryos.

Here too, clinical evidence was unable to confirm the hypothesis 24 . Moreover, basic research demonstrated a self-correction mechanism in mouse 25 and human embryos 26 – 29 that arose during embryogenesis that was cell lineage-specific to the embryonic cell lineage. In contrast, PGT-A biopsies are obtained from the extraembryonic-derived trophectoderm, rendering any diagnostic procedure at the blastocyst stage ineffective. In addition, mathematical modeling demonstrated that results from a single trophectoderm biopsy could not be extrapolated to the whole embryo 30 . Transfer of PGT-A “chromosomal-abnormal diagnosed embryos” has resulted in the births of over 400 chromosomal-normal offspring 20 , 21 .

In recent years, increasing attention has also been given to the quickly evolving understanding of how interdependent lifestyle and human fertility are 31 – 33 , including the influence of diet on the microbiome, as in many other areas of medicine.

The ethical significance of understanding human development

Whether in clinical medicine or in the research laboratory, human embryology has remained an ethical minefield, strongly influenced by socio-political and religious considerations. At the core of the controversy resides the special moral value of the human embryo, a subject that has come to the forefront again with the ascent of human embryonic stem cell research 34 . There is, however, little consensus as to how to answer a previously raised question: “ what is an embryo ?” 35 . The term pre-embryo, first introduced in 1986, was defined as the interval up to the appearance of the primitive streak, which marks biological individuation at ~14 days post-fertilization. This definition designated the period beyond 14 days as the time when a pre-embryo attains special moral status 36 , 37 . Paradoxically, the term pre-embryo has been replaced by the indiscriminate use of the term embryo, whether at preimplantation cleavage or blastocyst-stages or post-implantation before day 14. It was suggested that the distinction was important for ethical, moral, and biological relevance. The principal reason is simple: Until a pre-embryo becomes an embryo, there is no way of knowing whether implantation has taken place, whether a pregnancy is developing, whether there is a single pregnancy or twinning, or whether fertilization ended up in a benign (hydatidiform mole) or even in a malignant tumor (choriocarcinoma) 35 . Assigning advanced moral value to embryos at those early stages is, therefore, difficult to defend.

The past 10 years have witnessed innumerous ethical debates related to this subject, each with its own social, historical, and religious justifications, reflecting cultural diversities in human populations. Most are triggered by scientific breakthroughs. We summarize here the major ethical challenges preoccupying reproductive research and clinical practice.

We have already briefly referred to CRISPR/Cas9 genome editing. While the use of sc-RNA-seq to identify the molecular blueprint of human development has not elicited significant controversy, CRISPR/Cas9 genome editing of human embryos has been a topic of intense discussions and is currently permissible only in vitro 38 . An alleged attempt in China of implanting human genome-edited embryos into the uterus supposedly led to two births (one a twin birth). Though widely discussed in the media, neither attempt was published in the medical literature, and therefore cannot be verified 5 , 38 .

The ethical debates surrounding the 14-day rule, quiescent since the early IVF days, experienced a rebirth that was prompted by in vitro human embryo attachment studies and the emergence of synthetic human embryos. Within this context, we note that self-organizing embryo models are nothing more than cells in culture and are certainly not embryos. Regardless of scientific merits, in the U.S., the National Institutes of Health (NIH) currently prohibits the use of public funds for the study of synthetic embryos “for ethical reasons”. After being under an NIH moratorium for more than a year, research on chimeras is now, however, again permitted, though human/non-human primate chimeras remain prohibited.

These ongoing ethical debates mostly also mirror those surrounding the lack of U.S. federal funding for clinical IVF and related research, as well as hESCs-derived model embryos. In this context, the American Society for Reproductive Medicine (ASRM)’s Ethics in Embryo Research Task Force recently made an important statement: “ Scientific research using human embryos advances human health and provides vital insights into reproduction and disease ” 39 .

Provided certain guidelines and safeguards are followed, research with already existing embryos or embryos specifically produced for research should be ethically acceptable as a means of obtaining new knowledge that may benefit human health. ASRM also pointed out that scientists and society must understand which research questions necessitate the use of human embryos.

It is gratifying to acknowledge the history and vitality of ongoing debates, especially since they increasingly mimic decision-making processes in the medical field. These debates are meant to be based on cost-benefit and/or risk-benefit assessments. These debates will, unquestionably, continue and, indeed, considering that every intervention has consequences, must be decided based on careful considerations, including all relevant stakeholders and all parts of society.

Acknowledgements

We like to thank Min Yang, Jean Marx Santel, Adam Souza, and Amir Brivanlou, for data gathering and critical reading of the manuscript, and constructive criticism.

Author contributions

Both A.H.B. and N.G. have contributed to writing the manuscript.

Competing interests

A.H.B. and N.G. are co-founders of OvaNova Inc. A.H.B. is a co-founder of Rumi Scientific Inc.

Peer review information Nature Communications thanks Alfonso Martinez Arias, Annelien Bredenoord and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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• Published: 29 July 2021

The evolution of our understanding of human development over the last 10 years

• Ali H. Brivanlou   ORCID: orcid.org/0000-0002-1761-280X 1 &
• Norbert Gleicher   ORCID: orcid.org/0000-0002-0202-4167 2 , 3 , 4  

Nature Communications volume  12 , Article number:  4615 ( 2021 ) Cite this article

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• Developmental biology
• Embryogenesis

As it fulfills an irresistible need to understand our own origins, research on human development occupies a unique niche in scientific and medical research. In this Comment, we explore the progress in our understanding of human development over the past 10 years. The focus is on basic research, clinical applications, and ethical considerations.

What basic research has taught us about human development

Over the last decade, progress in understanding our own development was mostly driven by the emergence and combination of remarkable new technologies. New molecular biology tools such as single-cell RNA-sequencing (sc-RNA-seq) unveiled the earliest genetic signature of the three cell lineages of the human blastocyst and allowed for the discovery of human-specific signatures 1 , 2 , 3 . CRISPR/Cas9 genome editing has offered further access to in vitro functional studies in human blastocysts 4 . However, as we discuss below, an ethical line was crossed when a group claimed that genetically modified human embryos had been transferred, leading to births 5 when neither public opinion nor a consensus within the scientific community had been reached regarding whether crossing the germline in in vitro fertilization (IVF) was safe and ethically acceptable.

On the embryology side, the development of an in vitro attachment platform for human blastocysts offered a first glance into post-implantation events up to 12 days 1 , 3 , 5 , 6 . This paved the way for several important discoveries, including the observation that the human embryo can self-organize to generate embryonic and extraembryonic germ layers, yolk sac, and amniotic cavities in the absence of maternal influences 5 , 6 ; and the presence of a transient embryonic tissue of trophectodermal lineage, adjacent to the yolk sac, therefore named, yolk-sac trophectoderm ( ysTE ) 5 . The presence of these seemingly human-specific populations was independently confirmed by sc-RNA-seq 1 .

The marriage of stem cell biology with bioengineering gave birth to the field of synthetic embryology 7 , 8 , 9 , 10 , 11 , 12 , 13 . This technology uses human embryonic stem cells (hESCs) cultured on geometrically confined micropatterned substrates to generate 2D in vitro models of human conceptuses, such as models of the gastrula ( gastruloids ) 7 , 8 , 9 , 10 , 11 , 12 , 13 , or parts of the embryo, such as cerebroids and neuruloids 14 . Thousands of nearly identical self-organizing human embryonic structures allow for standardization and reproducibility, which cannot be achieved in standard organoid structures 15 . Cells within these structures can be tracked and quantified in real time with sub-cellular resolution, using sophisticated quantification code, including artificial intelligence 14 .

Human gastruloids induce formation of the primitive streak and have enabled the deciphering of the molecular network underlying gastrulation—the most crucial moment of our lives 7 , 8 , 9 , 10 , 11 , 12 , 13 . 3D models of human epiblasts can spontaneously break axial symmetry, thus providing an assay for the elucidation of molecular events underlying the emergence of antero–posterior polarity 11 , 16 . A highly homogenous population of self-organizing 3D models of amniotic ectoderm-like cells can be obtained by combining microfluidic and microculture approaches 17 .

Finally, the development of interspecies chimeras provided the most stringent in vivo validation of human embryo models 9 , 10 , 18 . Unimaginable in human models, inter-species chimeras have become the next best choice to test whether hESC behavior in self-organizing gastruloids , as observed on microchips, would also occur in an embryonic environment 10 , 18 , 19 . Human/bird chimeras generated from transplanting human gastruloids into early chick embryos in ovo unexpectedly proved more efficient than previous methods 9 , 19 . They allowed for the observation of an entire self-organizing embryonic axis in bird eggs 9 . As birds are closer to dinosaurs than to humans, this high rate of success with these chimeras further suggested that these early patterning events must be highly conserved.

Translational clinical applications that arose from basic research

The past 10 years bore witness to significant clinical progress in reproductive medicine, often translated from basic research. Successful human uterus transplantation and the subsequent birth of healthy offspring was, for example, only achieved after years of meticulous laboratory work in animals 10 . Significant improvements in cryopreservation technology for human eggs and ovarian tissue were also preceded by research in model systems 10 , 20 . Practical clinical applications have been developed for women in need of cancer treatment that are toxic to ovaries. In these cases, oocytes and/or ovarian tissue can be cryopreserved for later use in fertility treatments once the patient is cured of her cancer 21 . This ever-evolving technology has already proven to result in live births, and has also become an integral part of routine infertility treatments with IVF, giving rise to the brand-new concept of fertility extension through egg-freezing.

Diagnostic technologies to assess retrieved eggs and preimplantation-stage embryos in the IVF process have been disappointing. For example, tracking extended embryo culture to blastocyst-stage with time-lapse imaging failed to improve embryo selection 22 . That chromosomal-abnormal embryos increase with maternal (but not paternal) age has been interpreted to mean that chromosomal abnormalities were a principal cause for lower implantation chances and higher miscarriage risks among older women. This assumption led to the rapidly growing utilization of chromosomal testing of human embryos prior to embryo transfer in a procedure recently renamed preimplantation genetic testing for aneuploidy (PGT-A) 23 . The hypothesis behind PGT-A is to exclude chromosomal-abnormal embryos from the transfer, thereby improving implantation potentials of remaining euploid embryos.

Here too, clinical evidence was unable to confirm the hypothesis 24 . Moreover, basic research demonstrated a self-correction mechanism in mouse 25 and human embryos 26 , 27 , 28 , 29 that arose during embryogenesis that was cell lineage-specific to the embryonic cell lineage. In contrast, PGT-A biopsies are obtained from the extraembryonic-derived trophectoderm, rendering any diagnostic procedure at the blastocyst stage ineffective. In addition, mathematical modeling demonstrated that results from a single trophectoderm biopsy could not be extrapolated to the whole embryo 30 . Transfer of PGT-A “chromosomal-abnormal diagnosed embryos” has resulted in the births of over 400 chromosomal-normal offspring 20 , 21 .

In recent years, increasing attention has also been given to the quickly evolving understanding of how interdependent lifestyle and human fertility are 31 , 32 , 33 , including the influence of diet on the microbiome, as in many other areas of medicine.

The ethical significance of understanding human development

Whether in clinical medicine or in the research laboratory, human embryology has remained an ethical minefield, strongly influenced by socio-political and religious considerations. At the core of the controversy resides the special moral value of the human embryo, a subject that has come to the forefront again with the ascent of human embryonic stem cell research 34 . There is, however, little consensus as to how to answer a previously raised question: “ what is an embryo ?” 35 . The term pre-embryo, first introduced in 1986, was defined as the interval up to the appearance of the primitive streak, which marks biological individuation at ~14 days post-fertilization. This definition designated the period beyond 14 days as the time when a pre-embryo attains special moral status 36 , 37 . Paradoxically, the term pre-embryo has been replaced by the indiscriminate use of the term embryo, whether at preimplantation cleavage or blastocyst-stages or post-implantation before day 14. It was suggested that the distinction was important for ethical, moral, and biological relevance. The principal reason is simple: Until a pre-embryo becomes an embryo, there is no way of knowing whether implantation has taken place, whether a pregnancy is developing, whether there is a single pregnancy or twinning, or whether fertilization ended up in a benign (hydatidiform mole) or even in a malignant tumor (choriocarcinoma) 35 . Assigning advanced moral value to embryos at those early stages is, therefore, difficult to defend.

The past 10 years have witnessed innumerous ethical debates related to this subject, each with its own social, historical, and religious justifications, reflecting cultural diversities in human populations. Most are triggered by scientific breakthroughs. We summarize here the major ethical challenges preoccupying reproductive research and clinical practice.

We have already briefly referred to CRISPR/Cas9 genome editing. While the use of sc-RNA-seq to identify the molecular blueprint of human development has not elicited significant controversy, CRISPR/Cas9 genome editing of human embryos has been a topic of intense discussions and is currently permissible only in vitro 38 . An alleged attempt in China of implanting human genome-edited embryos into the uterus supposedly led to two births (one a twin birth). Though widely discussed in the media, neither attempt was published in the medical literature, and therefore cannot be verified 5 , 38 .

The ethical debates surrounding the 14-day rule, quiescent since the early IVF days, experienced a rebirth that was prompted by in vitro human embryo attachment studies and the emergence of synthetic human embryos. Within this context, we note that self-organizing embryo models are nothing more than cells in culture and are certainly not embryos. Regardless of scientific merits, in the U.S., the National Institutes of Health (NIH) currently prohibits the use of public funds for the study of synthetic embryos “for ethical reasons”. After being under an NIH moratorium for more than a year, research on chimeras is now, however, again permitted, though human/non-human primate chimeras remain prohibited.

These ongoing ethical debates mostly also mirror those surrounding the lack of U.S. federal funding for clinical IVF and related research, as well as hESCs-derived model embryos. In this context, the American Society for Reproductive Medicine (ASRM)’s Ethics in Embryo Research Task Force recently made an important statement: “ Scientific research using human embryos advances human health and provides vital insights into reproduction and disease ” 39 .

Provided certain guidelines and safeguards are followed, research with already existing embryos or embryos specifically produced for research should be ethically acceptable as a means of obtaining new knowledge that may benefit human health. ASRM also pointed out that scientists and society must understand which research questions necessitate the use of human embryos.

It is gratifying to acknowledge the history and vitality of ongoing debates, especially since they increasingly mimic decision-making processes in the medical field. These debates are meant to be based on cost-benefit and/or risk-benefit assessments. These debates will, unquestionably, continue and, indeed, considering that every intervention has consequences, must be decided based on careful considerations, including all relevant stakeholders and all parts of society.

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Acknowledgements

We like to thank Min Yang, Jean Marx Santel, Adam Souza, and Amir Brivanlou, for data gathering and critical reading of the manuscript, and constructive criticism.

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Ali H. Brivanlou

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• Norbert Gleicher

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Both A.H.B. and N.G. have contributed to writing the manuscript.

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Correspondence to Ali H. Brivanlou .

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Competing interests.

A.H.B. and N.G. are co-founders of OvaNova Inc. A.H.B. is a co-founder of Rumi Scientific Inc.

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Peer review information Nature Communications thanks Alfonso Martinez Arias, Annelien Bredenoord and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Brivanlou, A.H., Gleicher, N. The evolution of our understanding of human development over the last 10 years. Nat Commun 12 , 4615 (2021). https://doi.org/10.1038/s41467-021-24793-3

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Anthony Ong, Cornell University Rachel Razza, Syracuse University Kim Ferguson, Sarah Lawrence College Zoe Klemfus, University of California, Irvine Laura Wray Lake, University of California, Los Angeles Rochelle Dalla, University of Nebraska - Lincoln Alison Sidle Fuligni, California State University, Los Angeles Valentina Lucia La Rosa, University of Catania

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Research in Human Development seeks to promote an inclusive, integrative, and interdisciplinary approach to the study of human development across the entire lifespan. The integration of the person and their context across the life course is the focus of the scholarship promoted by this journal. Specifically, an interdisciplinary focus that incorporates biological, psychological, sociological, anthropological, economic, and historical perspectives will be stressed in the pages of RHD. To encompass such breadth, the publication will incorporate a variety of research methods, including quantitative, qualitative, and mixed methods approaches. The journal seeks to promote scholarship on the social, cultural, and national (global) contexts of human development across diverse ethnic and racial groups employing multiple methods. Finally, RHD seeks to promote scholarship that informs public policies and social programs that promote positive and healthy human development for all people. In short, by providing a forum for research that is lifespan-oriented, interdisciplinary, contextual, and methodologically diverse, the journal will continue to significantly advance the field of human development.

The audience consists of researchers, educators, policy makers, and practitioners in all fields which address human development.

Special Issue Proposals

RHD publishes thematic issues devoted to the integration of theory and research across the lifespan representing multiple disciplines and methodologies. This journal uses Routledge’s Submission Portal to manage the submission process. You will need an ORCiD ID to log in to the submission portal. If you do not already have an ORCiD account, creating one takes 30 seconds and will allow you to login to a variety of other publishers’ systems as well as uniquely identifying your contribution to the scholarly record.

We are particularly interested in proposals for special issues that provide cutting-edge perspectives on pressing topics such as gun violence, Autism, whole reading vs phonics, bullying, abortion rights and access, and global implications of climate change. We are also interested in special issues that focus on development in historically marginalized populations (e.g., racial/ethnic, LGBTQIA+, (dis)ability) and use less conventional analytical techniques (e.g., community-based participatory approaches, culturally responsive methods, person-centered analyses).

If you have an idea for a proposal, we recommend reaching out to the co-editors to talk through the feasibility and fit with RHD. Once you are ready to submit your proposal (no more than 5 single-spaced pages, please), it should describe:

• The theme for the issue and its significance for the field;
• How the collected papers meet the interdisciplinary, multi method, and lifespan goals of the journal;
• Biographical information of the editors, especially highlighting prior editorial experience;
• The titles and authors of each potential paper, as well as a paragraph describing the scope/questions/data source/analytic strategies of each paper;
• How the papers come together in important ways, as a collection, to inform the theme;
• List of proposed contributors and their titles and affiliations; and
• References, as appropriate

Most issues have 5 papers of about 25 pages each (not counting the title and abstract pages, but including everything else). The organization may vary by project. For example: a very brief introduction of a few pages, plus 5 empirical papers; or, a brief introduction, plus 1 theoretical/conceptual/literature-based manuscript and 4 empirical papers; or, a very brief introduction, plus 4 empirical pieces and a discussion essay. These proposals will be reviewed by the editors in consultation with the Editorial Board. Once a proposal has been reviewed and accepted, the manuscripts must be accompanied by a statement that they have not been published elsewhere and that the papers have not been submitted simultaneously for publication elsewhere. Authors are responsible for obtaining permission to reproduce copyrighted material from other sources and are required to sign an agreement for the transfer of copyright to the publisher. All accepted manuscripts, artwork, and photographs become the property of the publisher.

If you have a Special Issue idea or proposal, please send an email to Drs. Urban ( [email protected] )   and Linver ( [email protected] ).

Open Access

You have the option to publish open access in this journal via our Open Select publishing program. Publishing open access means that your article will be free to access online immediately on publication, increasing the visibility, readership and impact of your research. Articles published Open Select with Taylor & Francis typically receive 95% more citations* and over 7 times as many downloads** compared to those that are not published Open Select.

Your research funder or your institution may require you to publish your article open access. Visit our Author Services website to find out more about open access policies and how you can comply with these.

You will be asked to pay an article publishing charge (APC) to make your article open access and this cost can often be covered by your institution or funder. Use our APC finder to view the APC for this journal.

Please visit our Author Services website if you would like more information about our Open Select Program.

*Citations received up to 9th June 2021 for articles published in 2016-2020 in journals listed in Web of Science®. Data obtained on 9th June 2021, from Digital Science's Dimensions platform, available at https://app.dimensions.ai **Usage in 2018-2020 for articles published in 2016-2020.

Peer Review and Ethics

Taylor & Francis is committed to peer-review integrity and upholding the highest standards of review. Once your special issue proposal has been assessed for suitability by the editors, the guest editor(s) will be responsible for managing single blind peer review by independent, anonymous expert referees. If any of the issue authors have shared earlier versions of their manuscript on a preprint server, please be aware that anonymity cannot be guaranteed. Further information on our preprints policy and citation requirements can be found on our Preprints Author Services page which also contains our guidance on publishing ethics and more information about what to expect during peer review.

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1.11: Developmental Research Designs

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Learning Outcomes

• Compare advantages and disadvantages of developmental research designs (cross-sectional, longitudinal, and sequential)

Now you know about some tools used to conduct research about human development. Remember, research methods are tools that are used to collect information. But it is easy to confuse research methods and research design. Research design is the strategy or blueprint for deciding how to collect and analyze information. Research design dictates which methods are used and how. Developmental research designs are techniques used particularly in lifespan development research. When we are trying to describe development and change, the research designs become especially important because we are interested in what changes and what stays the same with age. These techniques try to examine how age, cohort, gender, and social class impact development.

Cross-sectional designs

The majority of developmental studies use cross-sectional designs because they are less time-consuming and less expensive than other developmental designs. Cross-sectional research designs are used to examine behavior in participants of different ages who are tested at the same point in time. Let’s suppose that researchers are interested in the relationship between intelligence and aging. They might have a hypothesis (an educated guess, based on theory or observations) that intelligence declines as people get older. The researchers might choose to give a certain intelligence test to individuals who are 20 years old, individuals who are 50 years old, and individuals who are 80 years old at the same time and compare the data from each age group. This research is cross-sectional in design because the researchers plan to examine the intelligence scores of individuals of different ages within the same study at the same time; they are taking a “cross-section” of people at one point in time. Let’s say that the comparisons find that the 80-year-old adults score lower on the intelligence test than the 50-year-old adults, and the 50-year-old adults score lower on the intelligence test than the 20-year-old adults. Based on these data, the researchers might conclude that individuals become less intelligent as they get older. Would that be a valid (accurate) interpretation of the results?

No, that would not be a valid conclusion because the researchers did not follow individuals as they aged from 20 to 50 to 80 years old. One of the primary limitations of cross-sectional research is that the results yield information about age differences not necessarily changes with age or over time. That is, although the study described above can show that in 2010, the 80-year-olds scored lower on the intelligence test than the 50-year-olds, and the 50-year-olds scored lower on the intelligence test than the 20-year-olds, the data used to come up with this conclusion were collected from different individuals (or groups of individuals). It could be, for instance, that when these 20-year-olds get older (50 and eventually 80), they will still score just as high on the intelligence test as they did at age 20. In a similar way, maybe the 80-year-olds would have scored relatively low on the intelligence test even at ages 50 and 20; the researchers don’t know for certain because they did not follow the same individuals as they got older.

It is also possible that the differences found between the age groups are not due to age, per se, but due to cohort effects. The 80-year-olds in this 2010 research grew up during a particular time and experienced certain events as a group. They were born in 1930 and are part of the Traditional or Silent Generation. The 50-year-olds were born in 1960 and are members of the Baby Boomer cohort. The 20-year-olds were born in 1990 and are part of the Millennial or Gen Y Generation. What kinds of things did each of these cohorts experience that the others did not experience or at least not in the same ways?

You may have come up with many differences between these cohorts’ experiences, such as living through certain wars, political and social movements, economic conditions, advances in technology, changes in health and nutrition standards, etc. There may be particular cohort differences that could especially influence their performance on intelligence tests, such as education level and use of computers. That is, many of those born in 1930 probably did not complete high school; those born in 1960 may have high school degrees, on average, but the majority did not attain college degrees; the young adults are probably current college students. And this is not even considering additional factors such as gender, race, or socioeconomic status. The young adults are used to taking tests on computers, but the members of the other two cohorts did not grow up with computers and may not be as comfortable if the intelligence test is administered on computers. These factors could have been a factor in the research results.

Another disadvantage of cross-sectional research is that it is limited to one time of measurement. Data are collected at one point in time and it’s possible that something could have happened in that year in history that affected all of the participants, although possibly each cohort may have been affected differently. Just think about the mindsets of participants in research that was conducted in the United States right after the terrorist attacks on September 11, 2001.

Longitudinal research designs

Longitudinal research involves beginning with a group of people who may be of the same age and background (cohort) and measuring them repeatedly over a long period of time. One of the benefits of this type of research is that people can be followed through time and be compared with themselves when they were younger; therefore changes with age over time are measured. What would be the advantages and disadvantages of longitudinal research? Problems with this type of research include being expensive, taking a long time, and subjects dropping out over time. Think about the film, 63 Up , part of the Up Series mentioned earlier, which is an example of following individuals over time. In the videos, filmed every seven years, you see how people change physically, emotionally, and socially through time; and some remain the same in certain ways, too. But many of the participants really disliked being part of the project and repeatedly threatened to quit; one disappeared for several years; another died before her 63rd year. Would you want to be interviewed every seven years? Would you want to have it made public for all to watch?

Longitudinal research designs are used to examine behavior in the same individuals over time. For instance, with our example of studying intelligence and aging, a researcher might conduct a longitudinal study to examine whether 20-year-olds become less intelligent with age over time. To this end, a researcher might give an intelligence test to individuals when they are 20 years old, again when they are 50 years old, and then again when they are 80 years old. This study is longitudinal in nature because the researcher plans to study the same individuals as they age. Based on these data, the pattern of intelligence and age might look different than from the cross-sectional research; it might be found that participants’ intelligence scores are higher at age 50 than at age 20 and then remain stable or decline a little by age 80. How can that be when cross-sectional research revealed declines in intelligence with age?

Since longitudinal research happens over a period of time (which could be short term, as in months, but is often longer, as in years), there is a risk of attrition. Attrition occurs when participants fail to complete all portions of a study. Participants may move, change their phone numbers, die, or simply become disinterested in participating over time. Researchers should account for the possibility of attrition by enrolling a larger sample into their study initially, as some participants will likely drop out over time. There is also something known as selective attrition— this means that certain groups of individuals may tend to drop out. It is often the least healthy, least educated, and lower socioeconomic participants who tend to drop out over time. That means that the remaining participants may no longer be representative of the whole population, as they are, in general, healthier, better educated, and have more money. This could be a factor in why our hypothetical research found a more optimistic picture of intelligence and aging as the years went by. What can researchers do about selective attrition? At each time of testing, they could randomly recruit more participants from the same cohort as the original members, to replace those who have dropped out.

The results from longitudinal studies may also be impacted by repeated assessments. Consider how well you would do on a math test if you were given the exact same exam every day for a week. Your performance would likely improve over time, not necessarily because you developed better math abilities, but because you were continuously practicing the same math problems. This phenomenon is known as a practice effect. Practice effects occur when participants become better at a task over time because they have done it again and again (not due to natural psychological development). So our participants may have become familiar with the intelligence test each time (and with the computerized testing administration).

Another limitation of longitudinal research is that the data are limited to only one cohort. As an example, think about how comfortable the participants in the 2010 cohort of 20-year-olds are with computers. Since only one cohort is being studied, there is no way to know if findings would be different from other cohorts. In addition, changes that are found as individuals age over time could be due to age or to time of measurement effects. That is, the participants are tested at different periods in history, so the variables of age and time of measurement could be confounded (mixed up). For example, what if there is a major shift in workplace training and education between 2020 and 2040 and many of the participants experience a lot more formal education in adulthood, which positively impacts their intelligence scores in 2040? Researchers wouldn’t know if the intelligence scores increased due to growing older or due to a more educated workforce over time between measurements.

Sequential research designs

Sequential research designs include elements of both longitudinal and cross-sectional research designs. Similar to longitudinal designs, sequential research features participants who are followed over time; similar to cross-sectional designs, sequential research includes participants of different ages. This research design is also distinct from those that have been discussed previously in that individuals of different ages are enrolled into a study at various points in time to examine age-related changes, development within the same individuals as they age, and to account for the possibility of cohort and/or time of measurement effects. In 1965, K. Warner Schaie [1] (a leading theorist and researcher on intelligence and aging), described particular sequential designs: cross-sequential, cohort sequential, and time-sequential. The differences between them depended on which variables were focused on for analyses of the data (data could be viewed in terms of multiple cross-sectional designs or multiple longitudinal designs or multiple cohort designs). Ideally, by comparing results from the different types of analyses, the effects of age, cohort, and time in history could be separated out.

Consider, once again, our example of intelligence and aging. In a study with a sequential design, a researcher might recruit three separate groups of participants (Groups A, B, and C). Group A would be recruited when they are 20 years old in 2010 and would be tested again when they are 50 and 80 years old in 2040 and 2070, respectively (similar in design to the longitudinal study described previously). Group B would be recruited when they are 20 years old in 2040 and would be tested again when they are 50 years old in 2070. Group C would be recruited when they are 20 years old in 2070 and so on.

Studies with sequential designs are powerful because they allow for both longitudinal and cross-sectional comparisons—changes and/or stability with age over time can be measured and compared with differences between age and cohort groups. This research design also allows for the examination of cohort and time of measurement effects. For example, the researcher could examine the intelligence scores of 20-year-olds in different times in history and different cohorts (follow the yellow diagonal lines in figure 3). This might be examined by researchers who are interested in sociocultural and historical changes (because we know that lifespan development is multidisciplinary). One way of looking at the usefulness of the various developmental research designs was described by Schaie and Baltes (1975) [2] : cross-sectional and longitudinal designs might reveal change patterns while sequential designs might identify developmental origins for the observed change patterns.

Since they include elements of longitudinal and cross-sectional designs, sequential research has many of the same strengths and limitations as these other approaches. For example, sequential work may require less time and effort than longitudinal research (if data are collected more frequently than over the 30-year spans in our example) but more time and effort than cross-sectional research. Although practice effects may be an issue if participants are asked to complete the same tasks or assessments over time, attrition may be less problematic than what is commonly experienced in longitudinal research since participants may not have to remain involved in the study for such a long period of time.

When considering the best research design to use in their research, scientists think about their main research question and the best way to come up with an answer. A table of advantages and disadvantages for each of the described research designs is provided here to help you as you consider what sorts of studies would be best conducted using each of these different approaches.

https://assessments.lumenlearning.co...essments/16509

[glossary-page] [glossary-term]attrition:[/glossary-term] [glossary-definition]occurs when participants fail to complete all portions of a study[/glossary-definition]

[glossary-term]cross-sectional research:[/glossary-term] [glossary-definition]used to examine behavior in participants of different ages who are tested at the same point in time; may confound age and cohort differences[/glossary-definition]

[glossary-term]longitudinal research:[/glossary-term] [glossary-definition]studying a group of people who may be of the same age and background (cohort), and measuring them repeatedly over a long period of time; may confound age and time of measurement effects[/glossary-definition]

[glossary-term]research design:[/glossary-term] [glossary-definition]the strategy or blueprint for deciding how to collect and analyze information; dictates which methods are used and how[/glossary-definition]

[glossary-term]selective attrition:[/glossary-term] [glossary-definition]certain groups of individuals may tend to drop out more frequently resulting in the remaining participants longer being representative of the whole population[/glossary-definition]

[glossary-term]sequential research design:[/glossary-term] [glossary-definition]combines aspects of cross-sectional and longitudinal designs, but also adding new cohorts at different times of measurement; allows for analyses to consider effects of age, cohort, time of measurement, and socio-historical change[/glossary-definition] [/glossary-page]

• Schaie, K.W. (1965). A general model for the study of developmental problems. Psychological Bulletin, 64(2), 92-107. ↵
• Schaie, K.W. & Baltes, B.P. (1975). On sequential strategies in developmental research: Description or Explanation. Human Development, 18: 384-390. ↵

Contributors and Attributions

• Modification, adaptation, and original content. Authored by : Margaret Clark-Plaskie for Lumen Learning. Provided by : Lumen Learning. License : CC BY-NC-SA: Attribution-NonCommercial-ShareAlike
• Research Methods in Developmental Psychology. Authored by : Angela Lukowski and Helen Milojevich. Provided by : University of Calfornia, Irvine. Located at : https://nobaproject.com/modules/research-methods-in-developmental-psychology?r=LDcyNTg0 . Project : The Noba Project. License : CC BY-NC-SA: Attribution-NonCommercial-ShareAlike
• Woman holding own photograph. Provided by : Pxhere. Located at : https://pxhere.com/en/photo/221167 . License : CC0: No Rights Reserved

Research in Developmental Psychology

What you’ll learn to do: examine how to do research in lifespan development.

How do we know what changes and stays the same (and when and why) in lifespan development? We rely on research that utilizes the scientific method so that we can have confidence in the findings. How data are collected may vary by age group and by the type of information sought. The developmental design (for example, following individuals as they age over time or comparing individuals of different ages at one point in time) will affect the data and the conclusions that can be drawn from them about actual age changes. What do you think are the particular challenges or issues in conducting developmental research, such as with infants and children? Read on to learn more.

Learning outcomes

• Explain how the scientific method is used in researching development
• Compare various types and objectives of developmental research
• Describe methods for collecting research data (including observation, survey, case study, content analysis, and secondary content analysis)
• Explain correlational research
• Describe the value of experimental research
• Compare the advantages and disadvantages of developmental research designs (cross-sectional, longitudinal, and sequential)
• Describe challenges associated with conducting research in lifespan development

Research in Lifespan Development

How do we know what we know.

An important part of learning any science is having a basic knowledge of the techniques used in gathering information. The hallmark of scientific investigation is that of following a set of procedures designed to keep questioning or skepticism alive while describing, explaining, or testing any phenomenon. Not long ago a friend said to me that he did not trust academicians or researchers because they always seem to change their story. That, however, is exactly what science is all about; it involves continuously renewing our understanding of the subjects in question and an ongoing investigation of how and why events occur. Science is a vehicle for going on a never-ending journey. In the area of development, we have seen changes in recommendations for nutrition, in explanations of psychological states as people age, and in parenting advice. So think of learning about human development as a lifelong endeavor.

Personal Knowledge

How do we know what we know? Take a moment to write down two things that you know about childhood. Okay. Now, how do you know? Chances are you know these things based on your own history (experiential reality), what others have told you, or cultural ideas (agreement reality) (Seccombe and Warner, 2004). There are several problems with personal inquiry or drawing conclusions based on our personal experiences.

Our assumptions very often guide our perceptions, consequently, when we believe something, we tend to see it even if it is not there. Have you heard the saying, “seeing is believing”? Well, the truth is just the opposite: believing is seeing. This problem may just be a result of cognitive ‘blinders’ or it may be part of a more conscious attempt to support our own views. Confirmation bias is the tendency to look for evidence that we are right and in so doing, we ignore contradictory evidence.

Philosopher Karl Popper suggested that the distinction between that which is scientific and that which is unscientific is that science is falsifiable; scientific inquiry involves attempts to reject or refute a theory or set of assumptions (Thornton, 2005). A theory that cannot be falsified is not scientific. And much of what we do in personal inquiry involves drawing conclusions based on what we have personally experienced or validating our own experience by discussing what we think is true with others who share the same views.

Science offers a more systematic way to make comparisons and guard against bias. One technique used to avoid sampling bias is to select participants for a study in a random way. This means using a technique to ensure that all members have an equal chance of being selected. Simple random sampling may involve using a set of random numbers as a guide in determining who is to be selected. For example, if we have a list of 400 people and wish to randomly select a smaller group or sample to be studied, we use a list of random numbers and select the case that corresponds with that number (Case 39, 3, 217, etc.). This is preferable to asking only those individuals with whom we are familiar to participate in a study; if we conveniently chose only people we know, we know nothing about those who had no opportunity to be selected. There are many more elaborate techniques that can be used to obtain samples that represent the composition of the population we are studying. But even though a randomly selected representative sample is preferable, it is not always used because of costs and other limitations. As a consumer of research, however, you should know how the sample was obtained and keep this in mind when interpreting results. It is possible that what was found was limited to that sample or similar individuals and not generalizable to everyone else.

Scientific Methods

The particular method used to conduct research may vary by discipline and since lifespan development is multidisciplinary, more than one method may be used to study human development. One method of scientific investigation involves the following steps:

• Determining a research question
• Reviewing previous studies addressing the topic in question (known as a literature review)
• Determining a method of gathering information
• Conducting the study
• Interpreting the results
• Drawing conclusions; stating limitations of the study and suggestions for future research
• Making the findings available to others (both to share information and to have the work scrutinized by others)

The findings of these scientific studies can then be used by others as they explore the area of interest. Through this process, a literature or knowledge base is established. This model of scientific investigation presents research as a linear process guided by a specific research question. And it typically involves quantitative research , which relies on numerical data or using statistics to understand and report what has been studied.

Another model of research, referred to as qualitative research, may involve steps such as these:

• Begin with a broad area of interest and a research question
• Gain entrance into a group to be researched
• Gather field notes about the setting, the people, the structure, the activities, or other areas of interest
• Ask open-ended, broad “grand tour” types of questions when interviewing subjects
• Modify research questions as the study continues
• Note patterns or consistencies
• Explore new areas deemed important by the people being observed
• Report findings

In this type of research, theoretical ideas are “grounded” in the experiences of the participants. The researcher is the student and the people in the setting are the teachers as they inform the researcher of their world (Glazer & Strauss, 1967). Researchers should be aware of their own biases and assumptions, acknowledge them, and bracket them in efforts to keep them from limiting accuracy in reporting. Sometimes qualitative studies are used initially to explore a topic and more quantitative studies are used to test or explain what was first described.

A good way to become more familiar with these scientific research methods, both quantitative and qualitative, is to look at journal articles, which are written in sections that follow these steps in the scientific process. Most psychological articles and many papers in the social sciences follow the writing guidelines and format dictated by the  American Psychological Association  (APA). In general, the structure follows: abstract (summary of the article), introduction or literature review, methods explaining how the study was conducted, results of the study, discussion and interpretation of findings, and references.

Link to Learning

Brené Brown is a bestselling author and social work professor at the University of Houston. She conducts grounded theory research by collecting qualitative data from large numbers of participants. In Brené Brown’s TED Talk The Power of Vulnerability , Brown refers to herself as a storyteller-researcher as she explains her research process and summarizes her results.

Research Methods and Objectives

The main categories of psychological research are descriptive, correlational, and experimental research. Research studies that do not test specific relationships between variables are called  descriptive, or qualitative, studies . These studies are used to describe general or specific behaviors and attributes that are observed and measured. In the early stages of research, it might be difficult to form a hypothesis, especially when there is not any existing literature in the area. In these situations designing an experiment would be premature, as the question of interest is not yet clearly defined as a hypothesis. Often a researcher will begin with a non-experimental approach, such as a descriptive study, to gather more information about the topic before designing an experiment or correlational study to address a specific hypothesis. Some examples of descriptive questions include:

• “How much time do parents spend with their children?”
• “How many times per week do couples have intercourse?”
• “When is marital satisfaction greatest?”

The main types of descriptive studies include observation, case studies, surveys, and content analysis (which we’ll examine further in the module). Descriptive research is distinct from  correlational research , in which psychologists formally test whether a relationship exists between two or more variables.  Experimental research  goes a step further beyond descriptive and correlational research and randomly assigns people to different conditions, using hypothesis testing to make inferences about how these conditions affect behavior. Some experimental research includes explanatory studies, which are efforts to answer the question “why” such as:

• “Why have rates of divorce leveled off?”
• “Why are teen pregnancy rates down?”
• “Why has the average life expectancy increased?”

Evaluation research is designed to assess the effectiveness of policies or programs. For instance, research might be designed to study the effectiveness of safety programs implemented in schools for installing car seats or fitting bicycle helmets. Do children who have been exposed to the safety programs wear their helmets? Do parents use car seats properly? If not, why not?

Research Methods

We have just learned about some of the various models and objectives of research in lifespan development. Now we’ll dig deeper to understand the methods and techniques used to describe, explain, or evaluate behavior.

All types of research methods have unique strengths and weaknesses, and each method may only be appropriate for certain types of research questions. For example, studies that rely primarily on observation produce incredible amounts of information, but the ability to apply this information to the larger population is somewhat limited because of small sample sizes. Survey research, on the other hand, allows researchers to easily collect data from relatively large samples. While this allows for results to be generalized to the larger population more easily, the information that can be collected on any given survey is somewhat limited and subject to problems associated with any type of self-reported data. Some researchers conduct archival research by using existing records. While this can be a fairly inexpensive way to collect data that can provide insight into a number of research questions, researchers using this approach have no control over how or what kind of data was collected.

Types of Descriptive Research

Observation.

Observational studies , also called naturalistic observation, involve watching and recording the actions of participants. This may take place in the natural setting, such as observing children at play in a park, or behind a one-way glass while children are at play in a laboratory playroom. The researcher may follow a checklist and record the frequency and duration of events (perhaps how many conflicts occur among 2-year-olds) or may observe and record as much as possible about an event as a participant (such as attending an Alcoholics Anonymous meeting and recording the slogans on the walls, the structure of the meeting, the expressions commonly used, etc.). The researcher may be a participant or a non-participant. What would be the strengths of being a participant? What would be the weaknesses?

In general, observational studies have the strength of allowing the researcher to see how people behave rather than relying on self-report. One weakness of self-report studies is that what people do and what they say they do are often very different. A major weakness of observational studies is that they do not allow the researcher to explain causal relationships. Yet, observational studies are useful and widely used when studying children. It is important to remember that most people tend to change their behavior when they know they are being watched (known as the Hawthorne effect ) and children may not survey well.

Case Studies

Case studies  involve exploring a single case or situation in great detail. Information may be gathered with the use of observation, interviews, testing, or other methods to uncover as much as possible about a person or situation. Case studies are helpful when investigating unusual situations such as brain trauma or children reared in isolation. And they are often used by clinicians who conduct case studies as part of their normal practice when gathering information about a client or patient coming in for treatment. Case studies can be used to explore areas about which little is known and can provide rich detail about situations or conditions. However, the findings from case studies cannot be generalized or applied to larger populations; this is because cases are not randomly selected and no control group is used for comparison. (Read The Man Who Mistook His Wife for a Hat by Dr. Oliver Sacks as a good example of the case study approach.)

Surveys  are familiar to most people because they are so widely used. Surveys enhance accessibility to subjects because they can be conducted in person, over the phone, through the mail, or online. A survey involves asking a standard set of questions to a group of subjects. In a highly structured survey, subjects are forced to choose from a response set such as “strongly disagree, disagree, undecided, agree, strongly agree”; or “0, 1-5, 6-10, etc.” Surveys are commonly used by sociologists, marketing researchers, political scientists, therapists, and others to gather information on many variables in a relatively short period of time. Surveys typically yield surface information on a wide variety of factors, but may not allow for an in-depth understanding of human behavior.

Surveys are useful in examining stated values, attitudes, opinions, and reporting on practices. However, they are based on self-report, or what people say they do rather than on observation, and this can limit accuracy. Validity refers to accuracy and reliability refers to consistency in responses to tests and other measures; great care is taken to ensure the validity and reliability of surveys.

Content Analysis

Content analysis  involves looking at media such as old texts, pictures, commercials, lyrics, or other materials to explore patterns or themes in culture. An example of content analysis is the classic history of childhood by Aries (1962) called “Centuries of Childhood” or the analysis of television commercials for sexual or violent content or for ageism. Passages in text or television programs can be randomly selected for analysis as well. Again, one advantage of analyzing work such as this is that the researcher does not have to go through the time and expense of finding respondents, but the researcher cannot know how accurately the media reflects the actions and sentiments of the population.

Secondary content analysis, or archival research, involves analyzing information that has already been collected or examining documents or media to uncover attitudes, practices, or preferences. There are a number of data sets available to those who wish to conduct this type of research. The researcher conducting secondary analysis does not have to recruit subjects but does need to know the quality of the information collected in the original study. And unfortunately, the researcher is limited to the questions asked and data collected originally.

Correlational and Experimental Research

Correlational research.

When scientists passively observe and measure phenomena it is called correlational research . Here, researchers do not intervene and change behavior, as they do in experiments. In correlational research, the goal is to identify patterns of relationships, but not cause and effect. Importantly, with correlational research, you can examine only two variables at a time, no more and no less.

So, what if you wanted to test whether spending money on others is related to happiness, but you don’t have $20 to give to each participant in order to have them spend it for your experiment? You could use a correlational design—which is exactly what Professor Elizabeth Dunn (2008) at the University of British Columbia did when she conducted research on spending and happiness. She asked people how much of their income they spent on others or donated to charity, and later she asked them how happy they were. Do you think these two variables were related? Yes, they were! The more money people reported spending on others, the happier they were.

Understanding Correlation

With a positive correlation , the two variables go up or down together. In a scatterplot, the dots form a pattern that extends from the bottom left to the upper right (just as they do in Figure 1). The r value for a positive correlation is indicated by a positive number (although, the positive sign is usually omitted). Here, the r value is .81. For the example above, the direction of the association is positive. This means that people who perceived the past month as being good reported feeling happier, whereas people who perceived the month as being bad reported feeling less happy.

A negative correlation is one in which the two variables move in opposite directions. That is, as one variable goes up, the other goes down. Figure 2 shows the association between the average height of males in a country (y-axis) and the pathogen prevalence (or commonness of disease; x-axis) of that country. In this scatterplot, each dot represents a country. Notice how the dots extend from the top left to the bottom right. What does this mean in real-world terms? It means that people are shorter in parts of the world where there is more disease. The r-value for a negative correlation is indicated by a negative number—that is, it has a minus (–) sign in front of it. Here, it is –.83.

Experimental Research

Experiments  are designed to test  hypotheses  (or specific statements about the relationship between  variables ) in a controlled setting in an effort to explain how certain factors or events produce outcomes. A variable is anything that changes in value. Concepts are operationalized  or transformed into variables in research which means that the researcher must specify exactly what is going to be measured in the study. For example, if we are interested in studying marital satisfaction, we have to specify what marital satisfaction really means or what we are going to use as an indicator of marital satisfaction. What is something measurable that would indicate some level of marital satisfaction? Would it be the amount of time couples spend together each day? Or eye contact during a discussion about money? Or maybe a subject’s score on a marital satisfaction scale? Each of these is measurable but these may not be equally valid or accurate indicators of marital satisfaction. What do you think? These are the kinds of considerations researchers must make when working through the design.

The experimental method is the only research method that can measure cause and effect relationships between variables. Three conditions must be met in order to establish cause and effect. Experimental designs are useful in meeting these conditions:

• The independent and dependent variables must be related.  In other words, when one is altered, the other changes in response. The independent variable is something altered or introduced by the researcher; sometimes thought of as the treatment or intervention. The dependent variable is the outcome or the factor affected by the introduction of the independent variable; the dependent variable  depends on the independent variable. For example, if we are looking at the impact of exercise on stress levels, the independent variable would be exercise; the dependent variable would be stress.
• The cause must come before the effect.  Experiments measure subjects on the dependent variable before exposing them to the independent variable (establishing a baseline). So we would measure the subjects’ level of stress before introducing exercise and then again after the exercise to see if there has been a change in stress levels. (Observational and survey research does not always allow us to look at the timing of these events which makes understanding causality problematic with these methods.)
• The cause must be isolated.  The researcher must ensure that no outside, perhaps unknown variables, are actually causing the effect we see. The experimental design helps make this possible. In an experiment, we would make sure that our subjects’ diets were held constant throughout the exercise program. Otherwise, the diet might really be creating a change in stress level rather than exercise.

A basic experimental design involves beginning with a sample (or subset of a population) and randomly assigning subjects to one of two groups: the  experimental group or the control group . Ideally, to prevent bias, the participants would be blind to their condition (not aware of which group they are in) and the researchers would also be blind to each participant’s condition (referred to as “ double blind “). The experimental group is the group that is going to be exposed to an independent variable or condition the researcher is introducing as a potential cause of an event. The control group is going to be used for comparison and is going to have the same experience as the experimental group but will not be exposed to the independent variable. This helps address the placebo effect, which is that a group may expect changes to happen just by participating. After exposing the experimental group to the independent variable, the two groups are measured again to see if a change has occurred. If so, we are in a better position to suggest that the independent variable caused the change in the dependent variable . The basic experimental model looks like this:

The major advantage of the experimental design is that of helping to establish cause and effect relationships. A disadvantage of this design is the difficulty of translating much of what concerns us about human behavior into a laboratory setting.

Developmental Research Designs

Now you know about some tools used to conduct research about human development. Remember,  research methods  are tools that are used to collect information. But it is easy to confuse research methods and research design. Research design is the strategy or blueprint for deciding how to collect and analyze information. Research design dictates which methods are used and how. Developmental research designs are techniques used particularly in lifespan development research. When we are trying to describe development and change, the research designs become especially important because we are interested in what changes and what stays the same with age. These techniques try to examine how age, cohort, gender, and social class impact development.

Cross-sectional designs

The majority of developmental studies use cross-sectional designs because they are less time-consuming and less expensive than other developmental designs. Cross-sectional research designs are used to examine behavior in participants of different ages who are tested at the same point in time. Let’s suppose that researchers are interested in the relationship between intelligence and aging. They might have a hypothesis (an educated guess, based on theory or observations) that intelligence declines as people get older. The researchers might choose to give a certain intelligence test to individuals who are 20 years old, individuals who are 50 years old, and individuals who are 80 years old at the same time and compare the data from each age group. This research is cross-sectional in design because the researchers plan to examine the intelligence scores of individuals of different ages within the same study at the same time; they are taking a “cross-section” of people at one point in time. Let’s say that the comparisons find that the 80-year-old adults score lower on the intelligence test than the 50-year-old adults, and the 50-year-old adults score lower on the intelligence test than the 20-year-old adults. Based on these data, the researchers might conclude that individuals become less intelligent as they get older. Would that be a valid (accurate) interpretation of the results?

No, that would not be a valid conclusion because the researchers did not follow individuals as they aged from 20 to 50 to 80 years old. One of the primary limitations of cross-sectional research is that the results yield information about age differences  not necessarily changes with age or over time. That is, although the study described above can show that in 2010, the 80-year-olds scored lower on the intelligence test than the 50-year-olds, and the 50-year-olds scored lower on the intelligence test than the 20-year-olds, the data used to come up with this conclusion were collected from different individuals (or groups of individuals). It could be, for instance, that when these 20-year-olds get older (50 and eventually 80), they will still score just as high on the intelligence test as they did at age 20. In a similar way, maybe the 80-year-olds would have scored relatively low on the intelligence test even at ages 50 and 20; the researchers don’t know for certain because they did not follow the same individuals as they got older.

It is also possible that the differences found between the age groups are not due to age, per se, but due to cohort effects. The 80-year-olds in this 2010 research grew up during a particular time and experienced certain events as a group. They were born in 1930 and are part of the Traditional or Silent Generation. The 50-year-olds were born in 1960 and are members of the Baby Boomer cohort. The 20-year-olds were born in 1990 and are part of the Millennial or Gen Y Generation. What kinds of things did each of these cohorts experience that the others did not experience or at least not in the same ways?

You may have come up with many differences between these cohorts’ experiences, such as living through certain wars, political and social movements, economic conditions, advances in technology, changes in health and nutrition standards, etc. There may be particular cohort differences that could especially influence their performance on intelligence tests, such as education level and use of computers. That is, many of those born in 1930 probably did not complete high school; those born in 1960 may have high school degrees, on average, but the majority did not attain college degrees; the young adults are probably current college students. And this is not even considering additional factors such as gender, race, or socioeconomic status. The young adults are used to taking tests on computers, but the members of the other two cohorts did not grow up with computers and may not be as comfortable if the intelligence test is administered on computers. These factors could have been a factor in the research results.

Another disadvantage of cross-sectional research is that it is limited to one time of measurement. Data are collected at one point in time and it’s possible that something could have happened in that year in history that affected all of the participants, although possibly each cohort may have been affected differently. Just think about the mindsets of participants in research that was conducted in the United States right after the terrorist attacks on September 11, 2001.

Longitudinal research designs

Longitudinal   research involves beginning with a group of people who may be of the same age and background (cohort) and measuring them repeatedly over a long period of time. One of the benefits of this type of research is that people can be followed through time and be compared with themselves when they were younger; therefore changes with age over time are measured. What would be the advantages and disadvantages of longitudinal research? Problems with this type of research include being expensive, taking a long time, and subjects dropping out over time. Think about the film, 63 Up , part of the Up Series mentioned earlier, which is an example of following individuals over time. In the videos, filmed every seven years, you see how people change physically, emotionally, and socially through time; and some remain the same in certain ways, too. But many of the participants really disliked being part of the project and repeatedly threatened to quit; one disappeared for several years; another died before her 63rd year. Would you want to be interviewed every seven years? Would you want to have it made public for all to watch?   

Longitudinal research designs are used to examine behavior in the same individuals over time. For instance, with our example of studying intelligence and aging, a researcher might conduct a longitudinal study to examine whether 20-year-olds become less intelligent with age over time. To this end, a researcher might give an intelligence test to individuals when they are 20 years old, again when they are 50 years old, and then again when they are 80 years old. This study is longitudinal in nature because the researcher plans to study the same individuals as they age. Based on these data, the pattern of intelligence and age might look different than from the cross-sectional research; it might be found that participants’ intelligence scores are higher at age 50 than at age 20 and then remain stable or decline a little by age 80. How can that be when cross-sectional research revealed declines in intelligence with age?

Since longitudinal research happens over a period of time (which could be short term, as in months, but is often longer, as in years), there is a risk of attrition. Attrition occurs when participants fail to complete all portions of a study. Participants may move, change their phone numbers, die, or simply become disinterested in participating over time. Researchers should account for the possibility of attrition by enrolling a larger sample into their study initially, as some participants will likely drop out over time. There is also something known as  selective attrition— this means that certain groups of individuals may tend to drop out. It is often the least healthy, least educated, and lower socioeconomic participants who tend to drop out over time. That means that the remaining participants may no longer be representative of the whole population, as they are, in general, healthier, better educated, and have more money. This could be a factor in why our hypothetical research found a more optimistic picture of intelligence and aging as the years went by. What can researchers do about selective attrition? At each time of testing, they could randomly recruit more participants from the same cohort as the original members, to replace those who have dropped out.

The results from longitudinal studies may also be impacted by repeated assessments. Consider how well you would do on a math test if you were given the exact same exam every day for a week. Your performance would likely improve over time, not necessarily because you developed better math abilities, but because you were continuously practicing the same math problems. This phenomenon is known as a practice effect. Practice effects occur when participants become better at a task over time because they have done it again and again (not due to natural psychological development). So our participants may have become familiar with the intelligence test each time (and with the computerized testing administration). Another limitation of longitudinal research is that the data are limited to only one cohort.

Sequential research designs

Sequential research designs include elements of both longitudinal and cross-sectional research designs. Similar to longitudinal designs, sequential research features participants who are followed over time; similar to cross-sectional designs, sequential research includes participants of different ages. This research design is also distinct from those that have been discussed previously in that individuals of different ages are enrolled into a study at various points in time to examine age-related changes, development within the same individuals as they age, and to account for the possibility of cohort and/or time of measurement effects. In 1965, K. Warner Schaie described particular sequential designs: cross-sequential, cohort sequential, and time-sequential. The differences between them depended on which variables were focused on for analyses of the data (data could be viewed in terms of multiple cross-sectional designs or multiple longitudinal designs or multiple cohort designs). Ideally, by comparing results from the different types of analyses, the effects of age, cohort, and time in history could be separated out.

Challenges Conducting Developmental Research

The previous sections describe research tools to assess development across the lifespan, as well as the ways that research designs can be used to track age-related changes and development over time. Before you begin conducting developmental research, however, you must also be aware that testing individuals of certain ages (such as infants and children) or making comparisons across ages (such as children compared to teens) comes with its own unique set of challenges. In the final section of this module, let’s look at some of the main issues that are encountered when conducting developmental research, namely ethical concerns, recruitment issues, and participant attrition.

Ethical Concerns

You may already know that Institutional Review Boards (IRBs) must review and approve all research projects that are conducted at universities, hospitals, and other institutions (each broad discipline or field, such as psychology or social work, often has its own code of ethics that must also be followed, regardless of institutional affiliation). An IRB is typically a panel of experts who read and evaluate proposals for research. IRB members want to ensure that the proposed research will be carried out ethically and that the potential benefits of the research outweigh the risks and potential harm (psychological as well as physical harm) for participants.

What you may not know though, is that the IRB considers some groups of participants to be more vulnerable or at-risk than others. Whereas university students are generally not viewed as vulnerable or at-risk, infants and young children commonly fall into this category. What makes infants and young children more vulnerable during research than young adults? One reason infants and young children are perceived as being at increased risk is due to their limited cognitive capabilities, which makes them unable to state their willingness to participate in research or tell researchers when they would like to drop out of a study. For these reasons, infants and young children require special accommodations as they participate in the research process. Similar issues and accommodations would apply to adults who are deemed to be of limited cognitive capabilities.

When thinking about special accommodations in developmental research, consider the informed consent process. If you have ever participated in scientific research, you may know through your own experience that adults commonly sign an informed consent statement (a contract stating that they agree to participate in research) after learning about a study. As part of this process, participants are informed of the procedures to be used in the research, along with any expected risks or benefits. Infants and young children cannot verbally indicate their willingness to participate, much less understand the balance of potential risks and benefits. As such, researchers are oftentimes required to obtain written informed consent from the parent or legal guardian of the child participant, an adult who is almost always present as the study is conducted. In fact, children are not asked to indicate whether they would like to be involved in a study at all (a process known as assent) until they are approximately seven years old. Because infants and young children cannot easily indicate if they would like to discontinue their participation in a study, researchers must be sensitive to changes in the state of the participant (determining whether a child is too tired or upset to continue) as well as to parent desires (in some cases, parents might want to discontinue their involvement in the research). As in adult studies, researchers must always strive to protect the rights and well-being of the minor participants and their parents when conducting developmental research.

Recruitment

An additional challenge in developmental science is participant recruitment. Recruiting university students to participate in adult studies is typically easy.  Unfortunately, young children cannot be recruited in this way. Given these limitations, how do researchers go about finding infants and young children to be in their studies?

The answer to this question varies along multiple dimensions. Researchers must consider the number of participants they need and the financial resources available to them, among other things. Location may also be an important consideration. Researchers who need large numbers of infants and children may attempt to recruit them by obtaining infant birth records from the state, county, or province in which they reside. Researchers can choose to pay a recruitment agency to contact and recruit families for them.  More economical recruitment options include posting advertisements and fliers in locations frequented by families, such as mommy-and-me classes, local malls, and preschools or daycare centers. Researchers can also utilize online social media outlets like Facebook, which allows users to post recruitment advertisements for a small fee. Of course, each of these different recruitment techniques requires IRB approval. And if children are recruited and/or tested in school settings, permission would need to be obtained ahead of time from teachers, schools, and school districts (as well as informed consent from parents or guardians).

And what about the recruitment of adults? While it is easy to recruit young college students to participate in research, some would argue that it is too easy and that college students are samples of convenience. They are not randomly selected from the wider population, and they may not represent all young adults in our society (this was particularly true in the past with certain cohorts, as college students tended to be mainly white males of high socioeconomic status). In fact, in the early research on aging, this type of convenience sample was compared with another type of convenience sample—young college students tended to be compared with residents of nursing homes! Fortunately, it didn’t take long for researchers to realize that older adults in nursing homes are not representative of the older population; they tend to be the oldest and sickest (physically and/or psychologically). Those initial studies probably painted an overly negative view of aging, as young adults in college were being compared to older adults who were not healthy, had not been in school nor taken tests in many decades, and probably did not graduate high school, let alone college. As we can see, recruitment and random sampling can be significant issues in research with adults, as well as infants and children. For instance, how and where would you recruit middle-aged adults to participate in your research?

Another important consideration when conducting research with infants and young children is attrition . Although attrition is quite common in longitudinal research in particular (see the previous section on longitudinal designs for an example of high attrition rates and selective attrition in lifespan developmental research), it is also problematic in developmental science more generally, as studies with infants and young children tend to have higher attrition rates than studies with adults.  Infants and young children are more likely to tire easily, become fussy, and lose interest in the study procedures than are adults. For these reasons, research studies should be designed to be as short as possible – it is likely better to break up a large study into multiple short sessions rather than cram all of the tasks into one long visit to the lab. Researchers should also allow time for breaks in their study protocols so that infants can rest or have snacks as needed. Happy, comfortable participants provide the best data.

Conclusions

Lifespan development is a fascinating field of study – but care must be taken to ensure that researchers use appropriate methods to examine human behavior, use the correct experimental design to answer their questions, and be aware of the special challenges that are part-and-parcel of developmental research. After reading this module, you should have a solid understanding of these various issues and be ready to think more critically about research questions that interest you. For example, what types of questions do you have about lifespan development? What types of research would you like to conduct? Many interesting questions remain to be examined by future generations of developmental scientists – maybe you will make one of the next big discoveries!

Lifespan development is the scientific study of how and why people change or remain the same over time. As we are beginning to see, lifespan development involves multiple domains and many ages and stages that are important in and of themselves, but that are also interdependent and dynamic and need to be viewed holistically. There are many influences on lifespan development at individual and societal levels (including genetics); cultural, generational, economic, and historical contexts are often significant. And how developmental research is designed and data are collected, analyzed, and interpreted can affect what is discovered about human development across the lifespan.

Lifespan Development Copyright © 2020 by Julie Lazzara is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Home / Online Bachelor’s Degree Programs / Online Bachelor’s in Human Development and Family Studies / Bachelor’s in Human Development and Family Studies Resources / Stages of Human Development: What It Is & Why It’s Important

What Is Human Development and Why Is It Important? What Is Human Development and Why Is It Important? What Is Human Development and Why Is It Important?

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Tables of Contents

• Eight Stages of Human Development?
• Theories of Human Development

Human Development vs. Developmental Psychology

What are the genetic factors that affect human growth and development, why do we study human growth and development.

Imagine two children born in the same town and the same year to families with similar socioeconomic statuses. One child grows up to be assertive and confident, while the other grows up to be timid and shy. The study of the stages of human development can help explain the reasons for these differences and much more.

What is human development, exactly? Human development is a branch of psychology with the goal of understanding people — how they develop, grow, and change throughout their lives. This discipline, which can help individuals better understand themselves and their relationships, is broad. As such, it can be used in various professional settings and career paths.

What Are the Eight Stages of Human Development?

If human development is the study of how people change throughout their lives, how and when does this development happen? Many scientists and psychologists have studied various aspects of human development, including ego psychologist Erik Erikson. He examined the impact of social experiences throughout an individual’s life and theorized that  psychosocial development happens in eight sequential parts . What are the eight stages of human development?

Stage 1 — Infancy: Trust vs. Mistrust

In the first stage of human development, infants learn to trust based on how well their caregivers meet their basic needs and respond when they cry. If an infant cries out to be fed, the parent can either meet this need by feeding and comforting the infant or not meet this need by ignoring the infant. When their needs are met, infants learn that relying on others is safe; when their needs go unmet, infants grow up to be less trusting.

Stage 2 — Toddlerhood: Autonomy vs. Shame and Doubt

In addition to autonomy versus shame and doubt, another way to think of the second stage is independence versus dependence. Like in the first stage, toddlers go through this stage responding to their caregivers. If caregivers encourage them to be independent and explore the world on their own, toddlers will grow up with a sense of self-efficacy. If the caregivers hover excessively or encourage dependence, these toddlers grow up with less confidence in their abilities.

For example, if a toddler wants to walk without assistance in a safe area, the caregiver should encourage this autonomy by allowing the independent behavior. If the caregiver insists on holding the toddler’s hand even when it’s not necessary, this attention can lead to doubt later in life.

Stage 3 — Preschool Years: Initiative vs. Guilt

During the preschool years, children learn to assert themselves and speak up when they need something. Some children may state that they’re sad because a friend stole their toy. If this assertiveness is greeted with a positive reaction, they learn that taking initiative is helpful behavior. However, if they’re made to feel guilty or ashamed for their assertiveness, they may grow up to be timid and less likely to take the lead.

Stage 4 — Early School Years: Industry vs. Inferiority

When children begin school, they start to compare themselves with peers. If children feel they’re accomplished in relation to peers, they develop strong self-esteem. If, however, they notice that other children have met milestones that they haven’t, they may struggle with self-esteem. For example, a first grader may notice a consistently worse performance on spelling tests when compared with peers. If this becomes a pattern, it can lead to feelings of inferiority.

The key components of Erikson’s model of human development include stage one, infancy, trust versus mistrust; stage two, toddlerhood, autonomy versus shame and doubt; stage three, preschool years, initiative versus guilt; stage four, early school years, industry versus inferiority; stage five, adolescence, identity versus role confusion; stage six, young adulthood, intimacy versus isolation; stage seven, middle adulthood, generativity versus stagnation; and stage eight, late adulthood, integrity versus despair.

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Stage 5 — Adolescence: Identity vs. Role Confusion

The adolescent stage is where the term “identity crisis” originated, and for good reason. Adolescence is all about developing a sense of self. Adolescents who can clearly identify who they are grow up with stronger goals and self-knowledge than teenagers who struggle to break free of their parents’ or friends’ influences. Adolescents who still deeply depend on their parents for social interaction and guidance may experience more role confusion than teenagers who pursue their own interests.

Stage 6 — Young Adulthood: Intimacy vs. Isolation

In young adulthood, which begins roughly at age 20, people begin to solidify their lifelong bonds; many people enter committed relationships or marriages, while others form lifelong friendships. People who can create and maintain these relationships reap the emotional benefits, while those who struggle to maintain relationships may suffer from isolation. A young adult who develops strong friendships in college may feel more intimacy than one who struggles to form and maintain close friendships.

Stage 7 — Middle Adulthood: Generativity vs. Stagnation

In middle adulthood, people tend to struggle with their contributions to society. They may be busy raising children or pursuing careers. Those who feel that they’re contributing experience generativity, which is the sense of leaving a legacy. On the other hand, those who don’t feel that their work or lives matter may experience feelings of stagnation. For example, a middle-aged adult who’s raising a family and working in a career that presumably helps people may feel more fulfilled than an adult who’s working at a day job that feels meaningless.

Stage 8 — Late Adulthood: Integrity vs. Despair

As adults reach the end of life, they look back on their lives and reflect. Adults who feel fulfilled by their lives, either through a successful family or a meaningful career, reach ego integrity, in which they can face aging and dying with peace. If older adults don’t feel that they’ve lived a good life, they risk falling into despair.

Other Theories of Human Development

Although widely used, Erikson’s psychosocial development theory has been critiqued for focusing too much on childhood. Critics claim that his emphasis makes the model less representative of the growth that people experienced in adulthood. Erikson’s model of the stages of human development is only one theory addressing growth and change throughout life, as many other psychologists have researched their own  theories of human development , including the following:

Cognitive Development

Jean Piaget developed the theory of cognitive development. Piaget’s theory is widely used in education programs to prepare teachers to instruct students in developmentally appropriate ways. The theory is based on four stages:

• Sensorimotor —  In the sensorimotor stage (birth to 2 years old), children learn object permanence, which is the understanding that people and objects still exist even when they’re out of view.
• Preoperational —  In the preoperational stage (2-7 years old), children develop symbolic thought, which is when they begin to progress from concrete to abstract thinking. Children in this stage often have imaginary friends.
• Concrete operational —  In the concrete operational stage (7-11 years old), children solidify their abstract thinking and begin to understand cause and effect and logical implications of actions.
• Formal operational —  In the formal operational stage (adolescence to adulthood), humans plan for the future, think hypothetically, and assume adult responsibilities.

Moral Development

Lawrence Kohlberg created a theory of human development based on moral development concepts. The theory comprises the following stages:

• Preconventional —  In the preconventional stage, people follow rules because they’re afraid of punishment and make choices only with their best interests in mind.
• Conventional —  In the conventional stage, people act to avoid society’s judgment and follow rules to maintain the systems and structures that are already in place.
• Postconventional —  In the postconventional stage, a genuine concern for the welfare of others and the greater good of society guides people.

Psychosexual Theory

Sigmund Freud popularized the  psychosexual theory . The theory comprises five stages:

• Oral —  In the oral stage (birth to 1 year old), children learn to suck and swallow and may experience conflict with weaning.
• Anal —  In the anal stage (1-3 years old), children learn to withhold or expel feces and may experience conflict with potty training.
• Phallic —  In the phallic stage (3-6 years old), children discover that their genitals can give them pleasure.
•   Latency —  In the latency stage (roughly 6 years old through puberty), they take a break from these physical stages and instead develop mentally and emotionally.
• Genital —  In the genital stage (puberty through adulthood), people learn to express themselves sexually.

Ideally, children move through each phase fluidly as their sexual libidos develop, but if they’re stuck in any of the phases, they may develop a fixation that hinders their development.

Behavioral Theory

The behavioral theory focuses solely on a person’s behaviors rather than the feelings that go alongside those behaviors. It suggests that behaviors are conditioned in an environment due to certain stimuli. Behavioral theorists believe that behavior determines feelings, so changing behaviors is important because this will in turn change feelings.

The  attachment theory  focuses on the deep relationships between people across their lifetime. An important attachment theory finding is that children must develop at least one strong bond in childhood to trust and develop relationships as adults. The attachment theory comprises four stages:

• Asocial or  pre-attachment   (birth to 6 weeks old)
• Indiscriminate attachment (6 weeks old to 7 months old)
• Specific or discriminate attachment (7-9 months old)
• Multiple attachments (10 months old or later)

Social Learning Theory

The social learning theory builds upon the behavioral theory and postulates that people learn best by observing the behavior of others. They watch how others act, view the consequences, and then make decisions regarding their own behavior accordingly. The four stages in this theory are:

• Reproduction

In the attention stage, people first notice the behavior of others. In the retention stage, they remember the behavior and the resulting consequences. In the reproduction stage, people develop the ability to imitate the behaviors they want to reproduce, and in the motivation stage, they perform these behaviors.

Sociocultural Theory

The  sociocultural theory  ties human development to the society or culture in which people live. It focuses on the contributions that society as a whole makes to individual human development. For example, children who are raised to play outdoors develop differently from children who are raised to play indoors.

An important part of this theory is the zone of proximal development, which is an area of knowledge and skills slightly more advanced than a child’s current level. The zone of proximal development helps teachers think about and plan instruction, so sociocultural theory plays a large role in preservice teacher training.

Resources: More Information on Theories of Human Development

• BetterHelp, “Behavioral Theory, Behavioral Psychology, or Behaviorism? How Behavior and Personality Intersect ”
• Encyclopedia Britannica, “Lawrence Kohlberg’s Stages of Moral Development”
• Healthline, “What Are Freud’s Psychosexual Stages of Development?”
• PositivePsychology.com, “What Is Attachment Theory? Bowlby’s 4 Stages Explained”
• Psychology Today , Social Learning Theory
• SimplyPsychology, “Lev Vygotsky’s Sociocultural Theory”
• SimplyPsychology, Theories of Psychology
• Verywell Mind, “The 4 Stages of Cognitive Development”

What are the differences between human development and developmental psychology? These terms are closely related. In fact, the study of developmental psychology is most people’s entry into human development.

Developmental psychology  is defined as a scientific approach to explaining growth, change, and consistency throughout a lifetime. It uses various frameworks to understand how people develop and transform throughout their lives. The goals of developmental psychology are to describe, explain, and optimize development to improve people’s lives. In the real world, developmental psychology is used in the study of physical, psychological, emotional, social, personality, and perceptual development.

The  study of developmental psychology  can lead to careers in several different fields. Developmental psychologists often work in colleges and universities and focus on research and teaching. Others work in healthcare facilities, clinics, assisted living facilities, hospitals, mental health clinics, or homeless shelters. In these applied settings, their focus is more on assessing, evaluating, and treating people. According to June 2020 data from PayScale, developmental  psychologists earn an average annual salary of about $68,000 .

One more key element of human growth and development left to explore is  genetics . Genetics influences the speed and way in which people develop, though other factors, such as parenting, education, experiences, and socioeconomic factors, are also at play. The multiple genetic factors that affect human growth and development include genetic interactions and sex chromosome abnormalities.

Genetic Interactions

Genes can act in an additive way or sometimes conflict with one another. For example, a child with one tall parent and one short parent may end up between the two of them, at average height. Other times, genes follow a dominant-recessive pattern. If one parent has brown hair and the other has red hair, the red hair gene is the dominant gene if their child has red hair.

Gene-Environment Interactions

Humans’ genetic information is always interacting with the environment, and sometimes this can impact development and growth. For example, if a child in utero is exposed to drugs, the child’s cognitive abilities may be impacted, thus changing the developmental process. In addition, even if a child’s genes would indicate a tall height, if that child experiences poor nutrition as children, it may impact their height.

Sex Chromosome Abnormalities

Sex chromosome abnormalities impact as many as 1 in 500 births. The following syndromes are examples of sex chromosome abnormalities that can impact development:

• Klinefelter syndrome  is the presence of an extra X chromosome in males, which can cause physical characteristics such as decreased muscle mass and reduced body hair and may cause learning disabilities.
• Fragile X syndrome  is caused by a mutation in the FMR1 gene that makes the X chromosome  appear fragile . It can cause intellectual disability, developmental delays, or distinctive physical features such as a long face.
• Turner syndrome  happens when one of the X chromosomes is missing or partially missing. It only affects females and results in physical characteristics like short stature and webbed neck.

Down Syndrome

Down syndrome  is another common example of how genetics can impact development. This chromosomal disorder may cause some individuals to experience physical or intellectual development differences. Down syndrome occurs at the 21st chromosomal site, in which people with Down syndrome have three chromosomes rather than two.

Those with Down syndrome often have different physical characteristics and may be prone to physical problems like heart defects and hearing problems. Most individuals with Down syndrome have intellectual impairment, but the degree of this impairment varies from person to person.

The top reasons for studying human development are to gain an understanding of your own life experience, help others understand what they’re going through, understand the relationship of society and individual growth, lead more effectively, and support the physical and mental health of others.

The study of human growth and development offers a wealth of value for personal and professional growth and understanding. Many reasons exist for why we study human growth and development.

Common benefits include the following:

• To  gain a better understanding  of one’s own life experiences. This can help people personally reach an understanding of what childhood events shaped their adulthood.
• To  gain knowledge  of how social context impacts development. This knowledge can be invaluable for professionals like teachers as they gain a deeper understanding of their students.
• To  help others understand and contextualize  the ups and downs of life. This helps therapists and psychologists better aid their clients in self-discovery.
• To  understand how societal change can support growth  and development. This understanding helps decision-makers in schools change the educational culture for the better.
• To  become a more effective research, teacher, or leader  in many different industries. Understanding human development deeply and in context has many professional benefits that can lead to greater insight.
• To  support the physical and mental health of individuals  throughout their life span. Professionals like doctors, nurses, and therapists must understand human growth and development to better support their clients.

Students may choose to study human growth and development because of its array of applications across many professional fields. For example, students who want to become elementary school teachers may take courses on the stages of human development to understand cognitive development and how children’s brains grow and change.

Human development is a wide-reaching and ever-changing discipline. A knowledge of human development can be invaluable to people personally as they continue to learn and grow throughout their lives and professionally as they learn to apply what they’ve learned to their careers.

Infographic Sources

Financial Express, “The Eight Stages of Human Development”

VeryWell Mind, “5 Reasons to Study Human Development”

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Study finds that human neuron signals flow in one direction

by Charité - Universitätsmedizin Berlin

Contrary to previous assumptions, nerve cells in the human neocortex are wired differently than in mice. Those are the findings of a new study conducted by Charité-Universitätsmedizin Berlin and published in the journal Science . The study found that human neurons communicate in one direction, while in mice, signals tend to flow in loops. This increases the efficiency and capacity of the human brain to process information. These discoveries could further the development of artificial neural networks.

The neocortex, a critical structure for human intelligence , is less than five millimeters thick. There, in the outermost layer of the brain, 20 billion neurons process countless sensory perceptions, plan actions, and form the basis of our consciousness. How do these neurons process all this complex information? That largely depends on how they are "wired" to each other.

More complex neocortex, different information processing

"Our previous understanding of neural architecture in the neocortex is based primarily on findings from animal models such as mice," explains Prof. Jörg Geiger, Director of the Institute for Neurophysiology at Charité. "In those models, the neighboring neurons frequently communicate with each other as if they are in dialogue. One neuron signals another, and then that one sends a signal back. That means the information often flows in recurrent loops."

The human neocortex is much thicker and more complex than that of a mouse. Nonetheless, researchers had previously assumed—in part due to lack of data—that it follows the same basic principles of connectivity. A team of Charité researchers led by Geiger has now used exceptionally rare tissue samples and state-of-the-art technology to demonstrate that this is not the case.

A clever method of listening in on neuronal communication

For the study, the researchers examined brain tissue from 23 people who had undergone neurosurgery at Charité to treat drug-resistant epilepsy. During surgery, it was medically necessary to remove brain tissue in order to gain access to the diseased structures beneath it. The patients had consented to the use of this access tissue for research purposes.

To be able to observe the flows of signals between neighboring neurons in the outermost layer of the human neocortex, the team developed an improved version of what is known as the "multipatch" technique. This allowed the researchers to listen in on the communications taking place between as many as ten neurons at once.

As a result, they were able to take the necessary number of measurements to map the network in the short time before the cells ceased their activity outside the body. In all, they analyzed the communication channels among nearly 1,170 neurons with about 7,200 possible connections.

Feed-forward instead of in cycles

The team found that only a small fraction of the neurons engaged in reciprocal dialogue with each other.

"In humans, the information tends to flow in one direction instead. It seldom returns to the starting point either directly or via cycles," explains Dr. Yangfan Peng, first author of the publication. He worked on the study at the Institute for Neurophysiology and is now based at the Department of Neurology and the Neuroscience Research Center at Charité. The team used a computer simulation that they devised according to the same principles underlying the human network architecture to demonstrate that this forward-directed signal flow has benefits in terms of processing data.

The researchers gave the artificial neural network a typical machine learning task: recognizing the correct numbers from audio recordings of spoken digits. The network model that mimicked the human structures achieved more correct responses to this speech recognition task than the one modeled on mice. It was also more efficient, with the same performance requiring the equivalent of 380 neurons in the mouse model, but only 150 in the human one.

An economic role model for AI?

"The directed network architecture we see in humans is more powerful and conserves resources because more independent neurons can handle different tasks simultaneously," Peng explains. "This means that the local network can store more information. It isn't clear yet whether our findings within the outermost layer of the temporal cortex extend to other cortical regions, or how well they might explain the unique cognitive abilities of humans."

In the past, AI developers have looked to biological models for inspiration in designing artificial neural networks, but have also optimized their algorithms independently of the biological models. "Many artificial neural networks already use some form of this forward-directed connectivity because it delivers better results for some tasks," Geiger says. "It's fascinating to see that the human brain also shows similar network principles. These insights into cost-efficient information processing in the human neocortex could provide further inspiration for refining AI networks."

About the study

The work was done in close cooperation between the basic research and clinical departments of Charité. Under the leadership of the Institute of Neurophysiology, the following were involved: the Department of Neurosurgery, the Department of Neurology with Experimental Neurology, the Institute of Integrative Neuroanatomy, the Department of Neuropathology, the Neuroscience Research Center, and the NeuroCure Cluster of Excellence, with support from the University Clinic for Neurosurgery at Evangelisches Klinikum Bethel and the Institute of Neuroinformatics at ETH Zurich.

About the method

When surgery is performed to treat drug-resistant (refractory) epilepsy, it is often medically necessary to remove brain tissue. The explicit consent of patients was required in order to examine this valuable tissue for the study that has just been published. The research group is profoundly grateful to the patients for their consent. The authors used what is known as the "patch-clamp" method to analyze synaptic communication between neurons.

In this technique, an ultra-thin glass pipette is attached to a single neuron under a microscope to measure or stimulate the cell's electrical activity. The study utilized an advanced form of this technique in which multiple of these micropipettes simultaneously record the activity and connectivity of up to ten neurons (the "multipatch" method).

To be able to position the pipettes precisely, the device is equipped with robot arms that enable movements in the nanometer range. The measurement process is highly challenging and labor-intensive. Using two devices in parallel allowed the team to study several hundred connections between the nerve cells for each tissue sample. The brain tissue can be preserved for up to two days outside the body in an artificial nutrient solution before activity ceases.

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Vanderbilt scientist collaborates with Cajal Institute in Spain to train a bank of AI models to identify memory formation signals in the brain

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An international research collaboration between Vanderbilt University and the Madrid-based de la Prida lab in the Cajal Institute led to the development of AI models that detect and analyze hippocampal ripples, which are considered biomarkers of memory.

The research discoveries, outlined in an article Communications Biology , could lead to new opportunities to detect seizures and neural changes in people with Alzheimer’s disease and other neurological disorders.  

Kari Hoffman , associate professor of psychology and biomedical engineering at Vanderbilt, and her Ph.D. student Saman Abbaspoor worked on the study with lead authors Adrian Rubio and Andrea Navas Olive from the de la Prida lab. Hoffman is also a faculty affiliate at the Vanderbilt Brain Institute and the Data Science Institute.

As the group’s research outlines, the study of brain oscillations has brought new understanding of brain function. Hippocampal ripples are a type of fast oscillations that underlie the organization of memories. They are affected in such neurological disorders as epilepsy and Alzheimer’s disease, so they are considered an electroencephalographic (EEG) biomarker. However, ripples exhibit various waveform features and properties that can be missed by standard spectral methods.

The researchers set out to gain a better understanding of patterns of brain activity after scientists in the neuroscience community called for the need to better automate, harmonize and improve the detection of ripples across a range of tasks and species. In the study, the authors used recordings obtained in laboratory mice to first train a toolbox of machine learning models.

They then tested the generalizability of the models using data from non-human primates that were collected at Vanderbilt by Abbaspoor and Hoffman as part of the  BRAIN Initiative . The researchers found that it is possible to train AI algorithms primarily on rodent data, and still manage highly accurate detection of ripples in primates with little to no additional training, suggesting that the AI models may be successful in humans. The model toolbox emerged as a result of a hackathon, which resulted in a short list for the best detection models. The group identified more than 100 possible models from the different architectures that are now available for application or retraining by other researchers.

“This bank of AI models will provide new applications in the field of neurotechnology and can be useful for detection and analysis of high-frequency oscillations in pathologies such as epilepsy, where they are considered clinical markers,” said Liset de la Prida, research professor at Instituto Cajal, CSIC.

“There is a great interest in taking advantage of AI to enable greater precision in detection of disease states and for oscillotherapeutics,” Hoffman added. “These methods offer the promise to go beyond detecting ‘where’ in the brain but also to detect and ultimately correct the ‘when and how’ of oscillopathies.”

See examples of oscillations outlined in the study through the Hoffman lab’s award-winning BRAIN Initiative video submission and extended video , which was recently highlighted in the NIH Director’s Blog .

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College of Education and Human Development

Ashley cray: outstanding undergraduate research award/outstanding student in individual and family studies.

Ashley Cray is the 2024 recipient of the Outstanding Undergraduate Research Award, as well as the Outstanding Student in Child Development and Family Relations, Individual and Family Studies concentration award from the University of Maine College of Education and Human Development. Cray will graduate with minors in education and music. During her time at UMaine she has been a member of All Maine Women, the University Singers, UMaine Renaissance, the Honors College Student Activities Board and Backcountry Squatters. Read more below.

Hometown: Readfield, Maine

High School: Maranacook High School

Parents: Cynthia Cushing and Chad Cray

Tell us about your undergraduate research experiences: For the past two years, I have worked with the Servant Heart Research Collaborative on the Attachment Theory Team. In 2016, the University of Maine Honors College Servant Heart Research Collaborative Attachment Theory Team began developing a six-module workshop to introduce attachment theory and other evidence-based family-strengthening practices to caregivers in Sierra Leone. Developed in response to the global movement to phase out institutional care and reintegrate children who have experienced trauma into families, one of the core competencies of the AT Workshop is that it is designed to be accessible to low-literacy and non-literate caregivers. In the years since, the AT Workshop has been regularly and successfully offered in Sierra Leone and has been adapted for Haiti and Uganda. 

In my time with the AT Team, I have worked with other students to research parenting styles in countries such as Sierra Leone, Haiti and Uganda, to adapt the Attachment Theory Workshop, and create additional resources for our partner organizations. More recently, I was awarded high honors for my Honors Thesis, titled “Program Evaluation of the International Attachment Theory Workshop: A Program Evaluation and Analysis of the Evaluation of People Who Are Low-And-Non-Literate . ” In this thesis, I researched and outlined best practices for evaluating people who are low-or-non-literate in human development training settings. Research on this topic is minimal and my thesis sheds light on the need for further research on the matter. 

In addition to my Honors thesis research, I worked with a team of fellow CHF seniors to research political action following school shootings in different states. We analyzed bills introduced and passed in different states following mass shootings to determine the kinds of legislation that were successful or unsuccessful in becoming law following these events. We presented our research, titled “The Impact of Shooter Attacks at U.S. Schools: An Analysis of Gun Legislation Introduced Following School Shootings,” at the UMaine Student Symposium on April 12, 2024.

Special thanks: Thank you to the professors who have supported and guided me over the last four years. You have helped me become the person I am today! Thank you to my peers, friends and family who have been sounding boards and sources of joy and inspiration on this journey. I would not have been able to do it without you all!

Favorite UMaine memory: My favorite UMaine memory is going on a concert tour of Italy with University Singers! We traveled to Rome, Florence, Venice and Lecco and got to experience Italy in the summer. I will always treasure the beautiful time we spent there and the wonderful music we were able to share with our audiences!

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• Risk Group Classification for Infectious Agents (ABSA)
• Select Agent Program
• Association for the Accreditation of Human Research Protection Programs
• Biosafety Discussion List