essay cloning is

• IELTS Scores
• Life Skills Test
• Find a Test Centre
• Alternatives to IELTS
• Find Student Housing
• General Training
• Academic Word List
• Topic Vocabulary
• Collocation
• Phrasal Verbs
• Writing eBooks
• Reading eBook
• All eBooks & Courses
• Sample Essays
• Human Cloning Essay

IELTS Human Cloning Essay

This is a model answer for a  human cloning  essay.

If you look at the task, the wording is slightly different from the common  'do you agree or disagree'  essay.

However, it is essentially asking the same thing.

As people live longer and longer, the idea of cloning human beings in order to provide spare parts is becoming a reality. The idea horrifies most people, yet it is no longer mere science fiction.

To what extent do you agree with such a procedure?

Have you any reservations?

Understanding the Question and Task

You are asked if you agree with human cloning to use their body parts (in other words, what are the benefits), and what reservations (concerns) you have (in other words, what are the disadvantages).

So the best way to answer this human cloning essay is probably to look at both sides of the issue as has been done in the model answer.

As always, you must read the question carefully to make sure you answer it fully and do not go off topic.

You are specifically being asked to discuss the issue of creating human clones to then use their body parts. If you write about other issues to do with human cloning, you may go off topic.

Model Human Cloning Essay

You should spend about 40 minutes on this task.

Write about the following topic:

Give reasons for your answer and include any relevant examples from your own experience or knowledge.

Write at least 250 words.

Model Answer for Human Cloning Essay

The cloning of animals has been occurring for a number of years now, and this has now opened up the possibility of cloning humans too. Although there are clear benefits to humankind of cloning to provide spare body parts, I believe it raises a number of worrying ethical issues.

Due to breakthroughs in medical science and improved diets, people are living much longer than in the past. This, though, has brought with it problems. As people age, their organs can fail so they need replacing. If humans were cloned, their organs could then be used to replace those of sick people. It is currently the case that there are often not enough organ donors around to fulfil this need, so cloning humans would overcome the issue as there would then be a ready supply.

However, for good reasons, many people view this as a worrying development. Firstly, there are religious arguments against it. It would involve creating other human beings and then eventually killing them in order to use their organs, which it could be argued is murder. This is obviously a sin according to religious texts. Also, dilemmas would arise over what rights these people have, as surely they would be humans just like the rest of us. Furthermore, if we have the ability to clone humans, it has to be questioned where this cloning will end. Is it then acceptable for people to start cloning relatives or family members who have died?

To conclude, I do not agree with this procedure due to the ethical issues and dilemmas it would create. Cloning animals has been a positive development, but this is where it should end.

(276 words)

The essay is well-organized, with a clear introducion which introduces the topic:

• The cloning of animals has been occurring for a number of years now, and this has now opened up the possibility of cloning humans too.

And it has a thesis statement that makes it clear exactly how the human cloning essay will be structured and what the candidate's opinion is:

• Although there are clear benefits to humankind of cloning to provide spare body parts, I believe it raises a number of worrying ethical issues.

The first body paragraph discusses the advantages of cloning humans, and then the second body paragraph looks at the problems associated with this. The change of direction to look at the other side is clearly marked with a transition word ("however") and a topic sentence:

• However, for good reasons, many people view this as a worrying development.

Other transition words are used effectively to guide the reader through the ideas in the human cloning essay: Firstly,.. Also,... Furthermore,...

The candidate demonstrates that they can use a mix of complex structures. For example:

• Due to breakthroughs in medical science and improved diets, people are living much longer than in the past.
• It would involve creating another human and then eventually killing it in order to use its organs, which it could be argued is murder.
• ...if we have the ability to clone humans, it has to be questioned where this cloning will end.

<<< Back

Next >>>

More Agree / Disagree Essays:

Ban Smoking in Public Places Essay: Should the government ban it?

Ban smoking in public places essay: The sample answer shows you how you can present the opposing argument first, that is not your opinion, and then present your opinion in the following paragraph.

IELTS Internet Essay: Is the internet damaging social interaction?

Internet Essay for IELTS on the topic of the Internet and social interaction. Included is a model answer. The IELTS test usually focuses on topical issues. You have to discuss if you think that the Internet is damaging social interaction.

Role of Schools Essay: How should schools help children develop?

This role of schools essay for IELTS is an agree disagree type essay where you have to discuss how schools should help children to develop.

Sample IELTS Writing: Is spending on the Arts a waste of money?

Sample IELTS Writing: A common topic in IELTS is whether you think it is a good idea for government money to be spent on the arts. i.e. the visual arts, literary and the performing arts, or whether it should be spent elsewhere, usually on other public services.

Return of Historical Objects and Artefacts Essay

This essay discusses the topic of returning historical objects and artefacts to their country of origin. It's an agree/disagree type IELTS question.

Free University Education Essay: Should it be paid for or free?

Free university education Model IELTS essay. Learn how to write high-scoring IELTS essays. The issue of free university education is an essay topic that comes up in the IELTS test. This essay therefore provides you with some of the key arguments about this topic.

Multinational Organisations and Culture Essay

Multinational Organisations and Culture Essay: Improve you score for IELTS Essay writing by studying model essays. This Essay is about the extent to which working for a multinational organisation help you to understand other cultures.

Dying Languages Essay: Is a world with fewer languages a good thing?

Dying languages essays have appeared in IELTS on several occasions, an issue related to the spread of globalisation. Check out a sample question and model answer.

Truthfulness in Relationships Essay: How important is it?

This truthfulness in relationships essay for IELTS is an agree / disagree type essay. You need to decide if it's the most important factor.

Extinction of Animals Essay: Should we prevent this from happening?

In this extinction of animals essay for IELTS you have to decide whether you think humans should do what they can to prevent the extinction of animal species.

Airline Tax Essay: Would taxing air travel reduce pollution?

Airline Tax Essay for IELTS. Practice an agree and disagree essay on the topic of taxing airlines to reduce low-cost air traffic. You are asked to decide if you agree or disagree with taxing airlines in order to reduce the problems caused.

Scientific Research Essay: Who should be responsible for its funding?

Scientific research essay model answer for Task 2 of the test. For this essay, you need to discuss whether the funding and controlling of scientific research should be the responsibility of the government or private organizations.

Paying Taxes Essay: Should people keep all the money they earn?

Paying Taxes Essay: Read model essays to help you improve your IELTS Writing Score for Task 2. In this essay you have to decide whether you agree or disagree with the opinion that everyone should be able to keep their money rather than paying money to the government.

Employing Older People Essay: Is the modern workplace suitable?

Employing Older People Essay. Examine model essays for IELTS Task 2 to improve your score. This essay tackles the issue of whether it it better for employers to hire younger staff rather than those who are older.

IELTS Sample Essay: Is alternative medicine ineffective & dangerous?

IELTS sample essay about alternative and conventional medicine - this shows you how to present a well-balanced argument. When you are asked whether you agree (or disagree), you can look at both sides of the argument if you want.

IELTS Vegetarianism Essay: Should we all be vegetarian to be healthy?

Vegetarianism Essay for IELTS: In this vegetarianism essay, the candidate disagrees with the statement, and is thus arguing that everyone does not need to be a vegetarian.

Internet vs Newspaper Essay: Which will be the best source of news?

A recent topic to write about in the IELTS exam was an Internet vs Newspaper Essay. The question was: Although more and more people read news on the internet, newspapers will remain the most important source of news. To what extent do you agree or disagree?

Essay for IELTS: Are some advertising methods unethical?

This is an agree / disagree type question. Your options are: 1. Agree 100% 2. Disagree 100% 3. Partly agree. In the answer below, the writer agrees 100% with the opinion. There is an analysis of the answer.

Examinations Essay: Formal Examinations or Continual Assessment?

Examinations Essay: This IELTS model essay deals with the issue of whether it is better to have formal examinations to assess student’s performance or continual assessment during term time such as course work and projects.

Technology Development Essay: Are earlier developments the best?

This technology development essay shows you a complex IELTS essay question that is easily misunderstood. There are tips on how to approach IELTS essay questions

Any comments or questions about this page or about IELTS? Post them here. Your email will not be published or shared.

Before you go...

Check out the ielts buddy band 7+ ebooks & courses.

Would you prefer to share this page with others by linking to it?

• Click on the HTML link code below.
• Copy and paste it, adding a note of your own, into your blog, a Web page, forums, a blog comment, your Facebook account, or anywhere that someone would find this page valuable.

Band 7+ eBooks

"I think these eBooks are FANTASTIC!!! I know that's not academic language, but it's the truth!"

Linda, from Italy, Scored Band 7.5

IELTS Modules:

Other resources:.

• All Lessons
• Band Score Calculator
• Writing Feedback
• Speaking Feedback
• Teacher Resources
• Free Downloads
• Recent Essay Exam Questions
• Books for IELTS Prep
• Student Housing
• Useful Links

Recent Articles

IELTS Essay: English as a Global Language

Apr 03, 24 03:49 PM

Alternatives to the IELTS Exam

Mar 22, 24 12:32 PM

Common Questions about the IELTS Speaking Test

Mar 09, 24 05:28 AM

Important pages

IELTS Writing IELTS Speaking IELTS Listening   IELTS Reading All Lessons Vocabulary Academic Task 1 Academic Task 2 Practice Tests

Connect with us

Copyright © 2022- IELTSbuddy All Rights Reserved

IELTS is a registered trademark of University of Cambridge, the British Council, and IDP Education Australia. This site and its owners are not affiliated, approved or endorsed by the University of Cambridge ESOL, the British Council, and IDP Education Australia.

An official website of the United States government

The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

• Publications
• Account settings

Preview improvements coming to the PMC website in October 2024. Learn More or Try it out now .

• Advanced Search
• Journal List
• Proc Natl Acad Sci U S A
• v.112(29); 2015 Jul 21

Cloning humans? Biological, ethical, and social considerations

Author contributions: F.J.A. wrote the paper.

There are, in mankind, two kinds of heredity: biological and cultural. Cultural inheritance makes possible for humans what no other organism can accomplish: the cumulative transmission of experience from generation to generation. In turn, cultural inheritance leads to cultural evolution, the prevailing mode of human adaptation. For the last few millennia, humans have been adapting the environments to their genes more often than their genes to the environments. Nevertheless, natural selection persists in modern humans, both as differential mortality and as differential fertility, although its intensity may decrease in the future. More than 2,000 human diseases and abnormalities have a genetic causation. Health care and the increasing feasibility of genetic therapy will, although slowly, augment the future incidence of hereditary ailments. Germ-line gene therapy could halt this increase, but at present, it is not technically feasible. The proposal to enhance the human genetic endowment by genetic cloning of eminent individuals is not warranted. Genomes can be cloned; individuals cannot. In the future, therapeutic cloning will bring enhanced possibilities for organ transplantation, nerve cells and tissue healing, and other health benefits.

Chimpanzees are the closest relatives of Homo sapiens , our species. There is a precise correspondence bone by bone between the skeletons of a chimpanzee and a human. Humans bear young like apes and other mammals. Humans have organs and limbs similar to birds, reptiles, and amphibians; these similarities reflect the common evolutionary origin of vertebrates. However, it does not take much reflection to notice the distinct uniqueness of our species. Conspicuous anatomical differences between humans and apes include bipedal gait and an enlarged brain. Much more conspicuous than the anatomical differences are the distinct behaviors and institutions. Humans have symbolic language, elaborate social and political institutions, codes of law, literature and art, ethics, and religion; humans build roads and cities, travel by motorcars, ships, and airplanes, and communicate by means of telephones, computers, and televisions.

Human Origins

The hominin lineage diverged from the chimpanzee lineage 6–7 Ma, and it evolved exclusively in the African continent until the emergence of Homo erectus , somewhat before 1.8 Ma. Shortly after its emergence in tropical or subtropical Africa, H. erectus spread to other continents. Fossil remains of H. erectus (sensu lato) are known from Africa, Indonesia (Java), China, the Middle East, and Europe. H. erectus fossils from Java have been dated at 1.81 ± 0.04 and 1.66 ± 0.04 Ma and from Georgia at 1.6–1.8 Ma ( 1 ). Anatomically distinctive H. erectus fossils have been found in Spain, deposited before 780,000 y ago, the oldest in southern Europe ( 2 ).

The transition from H. erectus to H. sapiens occurred around 400,000 y ago, although this date is not well determined owing to uncertainty as to whether some fossils are erectus or archaic forms of sapiens. H. erectus persisted for some time in Asia, until 250,000 y ago in China and perhaps until 100,000 ago in Java, and thus was contemporary with early members of its descendant species, H. sapiens. Fossil remains of Neandertal hominids ( Homo neanderthalensis ), with brains as large as those of H. sapiens , appeared in Europe earlier than 200,000 y ago and persisted until 30,000 or 40,000 y ago ( 3 , 4 ).

There is controversy about the origin of modern humans. Some anthropologists argue that the transition from H. erectus to archaic H. sapiens and later to anatomically modern humans occurred consonantly in various parts of the Old World. Proponents of this “multiregional model” emphasize fossil evidence showing regional continuity in the transition from H. erectus to archaic and then modern H. sapiens . Most anthropologists argue instead that modern humans first arose in Africa somewhat before 100,000 y ago and from there spread throughout the world, eventually replacing elsewhere the preexisting populations of H. erectus , H. neanderthalensis, and archaic H. sapiens . The African origin of modern humans is supported by a wealth of recent genetic evidence and is therefore favored by many evolutionists ( 2 , 4 ).

We know about these matters in three ways: by comparing living primates, including humans, with each other; by discovery and investigation of fossil remains of primates that lived in the past; and by comparing their DNA, proteins, and other molecules. DNA and proteins give us the best information about how closely related we are to each of the primates and those to each other. However, to know how the human lineage changed in anatomy and behavior over time as our ancestors became more and more human-like, we have to study fossils and the tools they used and made, as well as other remnants of their activities ( 2 , 5 ).

Humans live in groups that are socially organized and so do other primates. However, other primate societies do not approach the complexity of human social organization. A distinctive human social trait is culture, which may be understood as the set of nonstrictly biological human activities and creations. Culture includes social and political institutions, ways of doing things, religious and ethical traditions, language, common sense and scientific knowledge, art and literature, technology, and in general all of the creations of the human mind. The advent of culture has brought with it cultural evolution, a superorganic mode of evolution superimposed on the organic mode, that has become the dominant mode of human evolution. Cultural evolution has come about because of cultural inheritance, a distinctively human mode of achieving adaptation to the environment ( 2 , 6 , 7 ).

There are in mankind two kinds of heredity: the biological and the cultural. Biological inheritance in humans is very much like that in any other sexually reproducing organism; it is based on the transmission of genetic information encoded in DNA from one generation to the next by means of the sex cells. Cultural inheritance, on the other hand, is based on transmission of information by a teaching-learning process, which is in principle independent of biological parentage. Culture is transmitted by instruction and learning, by example and imitation, through books, newspapers, radio, television, and motion pictures, through works of art, and through any other means of communication. Culture is acquired by every person from parents, relatives, and neighbors and from the whole human environment. Acquired cultural traits may be beneficial but also toxic; for example, racial prejudice or religious bigotry.

Biological heredity is Mendelian or vertical; it is transmitted from parents to their children, and only inherited traits can be transmitted to the progeny. (New mutations are insignificant in the present context.) Cultural heredity is Lamarckian: acquired characters can be transmitted to the progeny. However, cultural heredity goes beyond Lamarckian heredity, because it is horizontal and oblique and not only vertical. Traits can be acquired from and transmitted to other members of the same generation, whether or not they are relatives, and also from and to all other individuals with whom a person has contact, whether they are from the same or from any previous or ensuing generation.

Cultural inheritance makes possible for people what no other organism can accomplish—the cumulative transmission of experience from generation to generation. Animals can learn from experience, but they do not transmit their experiences or their discoveries (at least not to any large extent) to the following generations. Animals have individual memory, but they do not have a “social memory.” Humans, on the other hand, have developed a culture because they can transmit cumulatively their experiences from generation to generation.

Cultural inheritance makes possible cultural evolution, a new mode of adaptation to the environment that is not available to nonhuman organisms. Organisms in general adapt to the environment by means of natural selection, by changing over generations their genetic constitution to suit the demands of the environment. However, humans, and humans alone, can also adapt by changing the environment to suit the needs of their genes. (Animals build nests and modify their environment also in other ways, but the manipulation of the environment by any nonhuman species is trivial compared with mankind's manipulation.) For the last few millennia, humans have been adapting the environments to their genes more often than their genes to the environments.

To extend its geographical habitat, or to survive in a changing environment, a population of organisms must become adapted, through slow accumulation of genetic variants sorted out by natural selection, to the new climatic conditions, different sources of food, different competitors, and so on. The discovery of fire and the use of shelter and clothing allowed humans to spread from the warm tropical and subtropical regions of the Old World to the whole Earth, except for the frozen wastes of Antarctica, without the anatomical development of fur or hair. Humans did not wait for genetic mutants promoting wing development; they have conquered the air in a somewhat more efficient and versatile way by building flying machines. People travel the rivers and the seas without gills or fins. The exploration of outer space has started without waiting for mutations providing humans with the ability to breathe with low oxygen pressures or to function in the absence of gravity; astronauts carry their own oxygen and specially equipped pressure suits. From their obscure beginnings in Africa, humans have become the most widespread and abundant species of mammal on earth. It was the appearance of culture as a superorganic form of adaptation that made mankind the most successful animal species.

Cultural adaptation has prevailed in mankind over biological adaptation because it is a more effective mode of adaptation; it is more rapid and it can be directed. A favorable genetic mutation newly arisen in an individual can be transmitted to a sizeable part of the human species only through innumerable generations. However, a new scientific discovery or technical achievement can be transmitted to the whole of mankind, potentially at least, in less than one generation. Witness the rapid spread of personal computers, iPhones, and the Internet. Moreover, whenever a need arises, culture can directly pursue the appropriate changes to meet the challenge. On the contrary, biological adaptation depends on the accidental availability of a favorable mutation, or of a combination of several mutations, at the time and place where the need arises ( 2 , 6 , 7 ).

Biological Evolution in Modern Humans

There is no scientific basis to the claim sometimes made that the biological evolution of mankind has stopped, or nearly so, at least in technologically advanced countries. It is asserted that the progress of medicine, hygiene, and nutrition have largely eliminated death before middle age; that is, most people live beyond reproductive age, after which death is inconsequential for natural selection. That mankind continues to evolve biologically can be shown because the necessary and sufficient conditions for biological evolution persist. These conditions are genetic variability and differential reproduction. There is a wealth of genetic variation in mankind. With the trivial exception of identical twins, developed from a single fertilized egg, no two people who live now, lived in the past, or will live in the future, are likely to be genetically identical. Much of this variation is relevant to natural selection ( 5 , 8 , 9 ).

Natural selection is simply differential reproduction of alternative genetic variants. Natural selection will occur in mankind if the carriers of some genotypes are likely to leave more descendants than the carriers of other genotypes. Natural selection consists of two main components: differential mortality and differential fertility; both persist in modern mankind, although the intensity of selection due to postnatal mortality has been somewhat attenuated.

Death may occur between conception and birth (prenatal) or after birth (postnatal). The proportion of prenatal deaths is not well known. Death during the early weeks of embryonic development may go totally undetected. However, it is known that no less than 20% of all ascertained human conceptions end in spontaneous abortion during the first 2 mo of pregnancy. Such deaths are often due to deleterious genetic constitutions, and thus they have a selective effect in the population. The intensity of this form of selection has not changed substantially in modern mankind, although it has been slightly reduced with respect to a few genes such as those involved in Rh blood group incompatibility.

Postnatal mortality has been considerably reduced in recent times in technologically advanced countries. For example, in the United States, somewhat less than 50% of those born in 1840 survived to age 45, whereas the average life expectancy for people born in the United States in 1960 is 78 y ( Table 1 ) ( 8 , 10 ). In some regions of the world, postnatal mortality remains quite high, although there it has also generally decreased in recent decades. Mortality before the end of reproductive age, particularly where it has been considerably reduced, is largely associated with genetic defects, and thus it has a favorable selective effect in human populations. Several thousand genetic variants are known that cause diseases and malformations in humans; such variants are kept at low frequencies due to natural selection.

Percent of Americans born between 1840 and 1960 surviving to ages 15 and 45

Reprinted from ref. 8 .

It might seem at first that selection due to differential fertility has been considerably reduced in industrial countries as a consequence of the reduction in the average number of children per family that has taken place. However, this is not so. The intensity of fertility selection depends not on the mean number of children per family, but on the variance in the number of children per family. It is clear why this should be so. Assume that all people of reproductive age marry and that all have exactly the same number of children. In this case, there would not be fertility selection whether couples all had very few or all had very many children. Assume, on the other hand, that the mean number of children per family is low, but some families have no children at all or very few, whereas others have many. In this case, there would be considerable opportunity for selection—the genotypes of parents producing many children would increase in frequency at the expense of those having few or none. Studies of human populations have shown that the opportunity for natural selection often increases as the mean number of children decreases. An extensive study published years ago showed that the index of opportunity for selection due to fertility was four times larger among United States women born in the 20th century, with an average of less than three children per woman, than among women in the Gold Coast of Africa or in rural Quebec, who had three times or more children on average ( Table 2 ) ( 8 , 11 ). There is no evidence that natural selection due to fertility has decreased in modern human populations.

Mean number of children per family and index of opportunity for fertility selection I f , in various human populations

I f is calculated as the variance divided by the square of the mean number of children. The opportunity for selection usually increases as the mean number of children decreases. Reprinted from ref. 8 .

Natural selection may decrease in intensity in the future, but it will not disappear altogether. As long as there is genetic variation and the carriers of some genotypes are more likely to reproduce than others, natural selection will continue operating in human populations. Cultural changes, such as the development of agriculture, migration from the country to the cities, environmental pollution, and many others, create new selective pressures. The pressures of city life are partly responsible for the high incidence of mental disorders in certain human societies. The point to bear in mind is that human environments are changing faster than ever owing precisely to the accelerating rate of cultural change, and environmental changes create new selective pressures, thus fueling biological evolution.

Natural selection is the process of differential reproduction of alternative genetic variants. In terms of single genes, variation occurs when two or more alleles are present in the population at a given gene locus. How much genetic variation exists in the current human population? The answer is “quite a lot,” as will be presently shown, but natural selection will take place only if the alleles of a particular gene have different effects on fitness; that is, if alternative alleles differentially impact the probability of survival and reproduction.

The two genomes that we inherit from each parent are estimated to differ at about one or two nucleotides per thousand. The human genome consists of somewhat more than 3 billion nucleotides ( 12 ). Thus, about 3–6 million nucleotides are different between the two genomes of each human individual, which is a lot of genetic polymorphism. Moreover, the process of mutation introduces new variation in any population every generation. The rate of mutation in the human genome is estimated to be about 10 −8 , which is one nucleotide mutation for every hundred million nucleotides, or about 30 new mutations per genome per generation. Thus, every human has about 60 new mutations (30 in each genome) that were not present in the parents. If we consider the total human population, that is 60 mutations per person multiplied by 7 billion people, which is about 420 billion new mutations per generation that are added to the preexisting 3–6 million polymorphic nucleotides per individual.

That is a lot of mutations, even if many are redundant. Moreover, we must remember that the polymorphisms that count for natural selection are those that impact the probability of survival and reproduction of their carriers. Otherwise, the variant nucleotides may increase or decrease in frequency by chance, a process that evolutionists call “genetic drift,” but will not be impacted by natural selection ( 2 , 12 , 13 ).

Genetic Disorders

More than 2,000 human diseases and abnormalities that have a genetic causation have been identified in the human population. Genetic disorders may be dominant, recessive, multifactorial, or chromosomal. Dominant disorders are caused by the presence of a single copy of the defective allele, so that the disorder is expressed in heterozygous individuals: those having one normal and one defective allele. In recessive disorders, the defective allele must be present in both alleles, that is, it is inherited from each parent to be expressed. Multifactorial disorders are caused by interaction among several gene loci; chromosomal disorders are due to the presence or absence of a full chromosome or a fragment of a chromosome ( 14 , 15 ).

Examples of dominant disorders are some forms of retinoblastoma and other kinds of blindness, achondroplastic dwarfism, and Marfan syndrome (which is thought to have affected President Lincoln). Examples of recessive disorders are cystic fibrosis, Tay-Sachs disease, and sickle cell anemia (caused by an allele that in heterozygous condition protects against malaria). Examples of multifactorial diseases are spina bifida and cleft palate. Among the most common chromosomal disorders are Down syndrome, caused by the presence of an extra chromosome 21, and various kinds due to the absence of one sex chromosome or the presence of an extra one, beyond the normal condition of XX for women and XY for men. Examples are Turner’s syndrome (XO) and Klinefelter’s syndrome (XXY) ( 16 ).

The incidence of genetic disorders expressed in the living human population is estimated to be no less than 2.56%, impacting about 180 million people. Natural selection reduces the incidence of the genes causing disease, more effectively in the case of dominant disorders, where all carriers of the gene will express the disease, than for recessive disorders, which are expressed only in homozygous individuals. Consider, for example, phenylketonuria (PKU), a lethal disease if untreated, due to homozygosis for a recessive gene, which has an incidence of 1 in 10,000 newborns or 0.01%. PKU is due to an inability to metabolize the amino acid phenylalanine with devastating mental and physical effects. A very elaborate diet free of phenylalanine allows the patient to survive and reproduce if started early in life. The frequency of the PKU allele is about 1%, so that in heterozygous conditions it is present in more than 100 million people, but only the 0.01% of people who are homozygous express the disease and are subject to natural selection. The reduction of genetic disorders due to natural selection is balanced with their increase due to the incidence of new mutations.

Let’s consider another example. Hereditary retinoblastoma is a disease attributed to a dominant mutation of the gene coding for the retinoblastoma protein, RB1, but it is actually due to a deletion in chromosome 13. The unfortunate child with this condition develops a tumorous growth during infancy that, without treatment, starts in one eye and often extends to the other eye and then to the brain, causing death before puberty. Surgical treatment now makes it possible to save the life of the child if the condition is detected sufficiently early, although often one or both eyes may be lost. The treated person can live a more or less normal life, marry, and procreate. However, because the genetic determination is dominant (a gene deletion), one half of the progeny will, on the average, be born with the same genetic condition and will have to be treated. Before modern medicine, every mutation for retinoblastoma arising in the human population was eliminated from the population in the same generation owing to the death of its carrier. With surgical treatment, the mutant condition can be preserved, and new mutations arising each generation are added to those arisen in the past (refs. 17 and 18 ; www.abedia.com/wiley/index.html ).

The proportion of individuals affected by any one serious hereditary infirmity is relatively small, but there are more than 2,000 known serious physical infirmities determined by genes. When all these hereditary ailments are considered together, the proportion of persons born who will suffer from a serious handicap during their lifetimes owing to their heredity is more than 2% of the total population, as pointed out above (refs. 15 , 16 , and 19 ; www.abedia.com/wiley/index.html ).

The problem becomes more serious when mental defects are taken into consideration. More than 2% of the population is affected by schizophrenia or a related condition known as schizoid disease, ailments that may be in some cases determined by a single mutant gene. Another 3% or so of the population suffer from mild mental retardation (IQ less than 70). More than 100 million people in the world suffer from mental impairments due in good part to the genetic endowment they inherited from their parents.

Natural selection also acts on a multitude of genes that do not cause disease. Genes impact skin pigmentation, hair color and configuration, height, muscle strength and body shape, and many other anatomical polymorphisms that are apparent, as well as many that are not externally obvious, such as variations in the blood groups, in the immune system, and in the heart, liver, kidney, pancreas, and other organs. It is not always known how natural selection impacts these traits, but surely it does and does it differently in different parts of the world or at different times, as a consequence of the development of new vaccines, drugs, and medical treatments, and also as a consequence of changes in lifestyle, such as the reduction of the number of smokers or the increase in the rate of obesity in a particular country.

Genetic Therapy

Where is human evolution going? Biological evolution is directed by natural selection, which is not a benevolent force guiding evolution toward sure success. Natural selection brings about genetic changes that often appear purposeful because they are dictated by the requirements of the environment. The end result may, nevertheless, be extinction—more than 99.9% of all species that ever existed have become extinct. Natural selection has no purpose; humans alone have purposes and they alone may introduce them into their evolution. No species before mankind could select its evolutionary destiny; mankind possesses techniques to do so, and more powerful techniques for directed genetic change are becoming available. Because we are self-aware, we cannot refrain from asking what lies ahead, and because we are ethical beings, we must choose between alternative courses of action, some of which may appear as good and others as bad.

The argument has been advanced that the biological endowment of mankind is rapidly deteriorating owing precisely to the improving conditions of life and to the increasing power of modern medicine. The detailed arguments that support this contention involve some mathematical exercises, but their essence can be simply presented. Genetic changes (i.e., point or chromosome mutations) arise spontaneously in humans and in other living species. The great majority of newly arising mutations are either neutral or harmful to their carriers; only a very small fraction are likely to be beneficial. In a human population under the so-called “natural” conditions, that is, without the intervention of modern medicine and technology, the newly arising harmful mutations are eliminated from the population more or less rapidly depending on how harmful they are. The more harmful the effect of a mutation, the more rapidly it will be eliminated from the population by the process of natural selection. However, owing to medical intervention and, more recently, because of the possibility of genetic therapy, the elimination of some harmful mutations from the population is no longer taking place as rapidly and effectively as it did in the past.

Molecular biology has introduced in modern medicine a new way to cure diseases, namely genetic therapy, direct intervention in the genetic makeup of an individual. Gene therapy can be somatic or germ line. Germ-line genetic therapy would seek to correct a genetic defect, not only in the organs or tissues impacted, but also in the germ line, so that the person treated would not transmit the genetic impairment to the descendants. As of now, no interventions of germ-line therapy are seriously sought by scientists, physicians, or pharmaceutical companies.

The possibility of gene therapy was first anticipated in 1972 ( 20 ). The possible objectives are to correct the DNA of a defective gene or to insert a new gene that would allow the proper function of the gene or DNA to take place. In the case of a harmful gene, the objective would be to disrupt the gene that is not functioning properly.

The eminent biologist E. O. Wilson (2014) has stated, many would think somewhat hyperbolically, that the issue of how much to use genetic engineering to direct our own evolution, is “the greatest moral dilemma since God stayed the hand of Abraham” ( 21 ).

The first successful interventions of gene therapy concerned patients suffering from severe combined immunodeficiency (SCID), first performed in a 4-y-old girl at the National Institutes of Health in 1990 ( 22 ), soon followed by successful trials in other countries ( 23 ). Treatments were halted temporarily from 2000 to 2002 in Paris, when 2 of about 12 treated children developed a leukemia-like condition, which was indeed attributed to the gene therapy treatment. Since 2004, successful clinical trials for SCID have been performed in the United States, United Kingdom, France, Italy, and Germany ( 24 , 25 ).

Gene therapy treatments are still considered experimental. Successful clinical trials have been performed in patients suffering from adrenoleukodystrophy, Parkinson’s disease, chronic lymphocytic leukemia, acute lymphocytic leukemia, multiple myeloma, and hemophilia ( 26 , 27 ). Initially, the prevailing gene therapy methods involved recombinant viruses, but nonviral methods (transfection molecules) have become increasingly successful. Since 2013, US pharmaceutical companies have invested more than $600 million in gene therapy ( 28 ). However, in addition to the huge economic costs, technical hurdles remain. Frequent negative effects include immune response against an extraneous object introduced into human tissues, leukemia, tumors, and other disorders provoked by vector viruses. Moreover, the genetic therapy corrections are often short lived, which calls for multiple rounds of treatment, thereby increasing costs and other handicaps. In addition, many of the most common genetic disorders are multifactorial and are thus beyond current gene therapy treatment. Examples are diabetes, high blood pressure, heart disease, arthritis, and Alzheimer’s disease, which at the present state of knowledge and technology are not suitable for gene therapy.

If a genetic defect is corrected in the affected cells, tissues, or organs, but not in the germ line, the ova or sperm produced by the individual will transmit the defect to the progeny. A deleterious gene that might have been reduced in frequency or eliminated from the population, owing to the death or reduced fertility of the carrier, will now persist in the population and be added to its load of hereditary diseases. A consequence of genetic therapy is that the more hereditary diseases and defects are cured today, the more of them will be there to be cured in the succeeding generations. This consequence follows not only from gene therapy but also from typical medical treatments.

The Nobel laureate geneticist H. J. Muller eloquently voiced this concern about the cure, whether through genetic therapy or traditional medical treatment, of genetic ailments. “The more sick people we now cure and allow them to reproduce, the more there will be to cure in the future.” The fate toward which mankind is drifting is painted by Muller in somber colors. “The amount of genetically caused impairment suffered by the average individual…must by that time have grown….[P]eople’s time and energy…would be devoted chiefly to the effort to live carefully, to spare and to prop up their own feebleness, to soothe their inner disharmonies and, in general, to doctor themselves as effectively as possible. For everyone would be an invalid, with his own special familial twists….” (ref. 29 ; Fig. 1 ).

The bionic human, on the cover of Science : an image that could represent how H. J. Muller anticipates the human condition, a few centuries hence, showing the accumulation of physical handicaps as a consequence of the medical cure of hereditary diseases. Image by Cameron Slayden and Nathalie Cary; reprinted with permission from AAAS.

It must be pointed out that the population genetic consequences of curing hereditary diseases are not as immediate (“a few centuries hence”) as Muller anticipates. Consider, as a first example, we look at the recessive hereditary condition of PKU. The estimated frequency of the gene is q = 0.01; the expected number of humans born with PKU is q 2 = 0.0001, 1 for every 10,000 births. If all PKU individuals are cured all over the world and all of them leave as many descendants, on the average, as other humans, the frequency of the PKU allele will double after 1/q = 1/0.01 = 100 generations. If we assume 25 y per generation, we conclude that after 2,500 y, the frequency of the PKU allele will be q = 0.02, and q 2 = 0.0004, so that 4 of every 10,000 persons, rather than only 1, will be born with PKU.

In the case of dominant lethal diseases, the incidence is determined by the mutation frequency of the normal to the disease allele, which is typically of the order of m = 10 −6 –10 −8 , or between one in a million and one in one hundred million. Assuming the highest rate of m = 10 −6 , the incidence of the disease after 100 generations will become 1 for every 10,000 births. It would therefore seem likely that much earlier than 2,500 y, humans are likely to find ways of correcting hereditary ailments in the germ line, thereby stopping their transmission.

It must be pointed out that, although the proportion of individuals affected by any one serious hereditary infirmity is relatively small, there are many such hereditary ailments, which on the aggregate make the problem very serious. The problem becomes more serious when mental defects are taken into consideration. As pointed out above, more than 100 million people in the world suffer from mental impairments due in good part to the genetic endowment they inherited from their parents.

Human cloning may refer to “therapeutic cloning,” particularly the cloning of embryonic cells to obtain organs for transplantation or for treating injured nerve cells and other health purposes. Human cloning more typically refers to “reproductive cloning,” the use of somatic cell nuclear transfer (SCNT) to obtain eggs that could develop into adult individuals.

Human cloning has occasionally been suggested as a way to improve the genetic endowment of mankind, by cloning individuals of great achievement, for example, in sports, music, the arts, science, literature, politics, and the like, or of acknowledged virtue. These suggestions seemingly have never been taken seriously. However, some individuals have expressed a wish, however unrealistic, to be cloned, and some physicians have on occasion advertised that they were ready to carry out the cloning ( 30 ). The obstacles and drawbacks are many and insuperable, at least at the present state of knowledge.

Biologists use the term cloning with variable meanings, although all uses imply obtaining copies more or less precise of a biological entity. Three common uses refer to cloning genes, cloning cells, and cloning individuals. Cloning an individual, particularly in the case of a multicellular organism, such as a plant or an animal, is not strictly possible. The genes of an individual, the genome, can be cloned, but the individual itself cannot be cloned, as it will be made clear below.

Cloning genes or, more generally, cloning DNA segments is routinely done in many genetics and pharmaceutical laboratories throughout the world ( 12 , 31 ). Technologies for cloning cells in the laboratory are seven decades old and are used for reproducing a particular type of cell, for example a skin or a liver cell, in order to investigate its characteristics.

Individual human cloning occurs naturally in the case of identical twins, when two individuals develop from a single fertilized egg. These twins are called identical, precisely because they are genetically identical to each other.

The sheep Dolly, cloned in July 1996, was the first mammal artificially cloned using an adult cell as the source of the genotype. Frogs and other amphibians were obtained by artificial cloning as early as 50 y earlier ( 32 ).

Cloning an animal by SCNT proceeds as follows. First, the genetic information in the egg of a female is removed or neutralized. Somatic (i.e., body) cells are taken from the individual selected to be cloned, and the cell nucleus (where the genetic information is stored) of one cell is transferred with a micropipette into the host oocyte. The egg, so “fertilized,” is stimulated to start embryonic development ( 33 ).

Can a human individual be cloned? The correct answer is, strictly speaking, no. What is cloned are the genes, not the individual; the genotype, not the phenotype. The technical obstacles are immense even for cloning a human’s genotype.

Ian Wilmut, the British scientist who directed the cloning project, succeeded with Dolly only after 270 trials. The rate of success for cloning mammals has notably increased over the years without ever reaching 100%. The animals presently cloned include mice, rats, goats, sheep, cows, pigs, horses, and other mammals. The great majority of pregnancies end in spontaneous abortion ( 34 ). Moreover, as Wilmut noted, in many cases, the death of the fetus occurs close to term, with devastating economic, health, and emotional consequences in the case of humans ( 35 ).

In mammals, in general, the animals produced by cloning suffer from serious health handicaps, among others, gross obesity, early death, distorted limbs, and dysfunctional immune systems and organs, including liver and kidneys, and other mishaps. Even Dolly had to be euthanized early in 2003, after only 6 y of life, because her health was rapidly decaying, including progressive lung disease and arthritis ( 35 , 36 ).

The low rate of cloning success may improve in the future. It may be that the organ and other failures of those that reach birth will be corrected by technical advances. Human cloning would still face ethical objections from a majority of concerned people, as well as opposition from diverse religions. Moreover, there remains the limiting consideration asserted earlier: it might be possible to clone a person’s genes, but the individual cannot be cloned. The character, personality, and the features other than anatomical and physiological that make up the individual are not precisely determined by the genotype.

The Genotype and the Individual

The genetic makeup of an individual is its genotype. The phenotype refers to what the individual is, which includes not only the individual’s external appearance or anatomy, but also its physiology, as well as behavioral predispositions and attributes, encompassing intellectual abilities, moral values, aesthetic preferences, religious values, and, in general, all other behavioral characteristics or features, acquired by experience, imitation, learning, or in any other way throughout the individual’s life, from conception to death. The phenotype results from complex networks of interactions between the genes and the environment.

A person’s environmental influences begin, importantly, in the mother’s womb and continue after birth, through childhood, adolescence, and the whole life. Impacting behavioral experiences are associated with family, friends, schooling, social and political life, readings, aesthetic and religious experiences, and every event in the person’s life, whether conscious or not. The genotype of a person has an unlimited number, virtually infinite, of possibilities to be realized, which has been called the genotype’s “norm of reaction,” only one of which will be the case in a particular individual ( 37 ). If an adult person is cloned, the disparate life circumstances experienced many years later would surely result in a very different individual, even if anatomically the individual would resemble the genome’s donor at a similar age.

An illustration of environmental effects on the phenotype, and of interactions between the genotype and the environment, is shown in Fig. 2 ( 38 ). Three plants of the cinquefoil, Potentilla glandulosa , were collected in California—one on the coast at about 100 ft above sea level (Stanford), the second at about 4,600 ft (Mather), and the third in the Alpine zone of the Sierra Nevada at about 10,000 ft above sea level (Timberline). From each plant, three cuttings were obtained in each of several replicated experiments, which were planted in three experimental gardens at different altitudes, the same gardens from which the plants were collected. The division of one plant ensured that all three cuttings planted at different altitudes had the same genotype; that is, they were genetic clones from one another. ( P. glandulosa , like many other plants, can be reproduced by cuttings, which are genetically identical.)

Interacting effects of the genotype and the environment on the phenotype of the cinquefoil Pontentilla glandulosa . Cuttings of plants collected at different altitudes were planted in three different experimental gardens. Plants in the same row are genetically identical because they have been grown from cuttings of a single plant; plants in the same column are genetically different but have been grown in the same experimental garden. Reprinted with permission from ref. 13 .

Comparison of the plants in any row shows how a given genotype gives rise to different phenotypes in different environments. Genetically identical plants (for example, those in the bottom row) may prosper or not, even die, depending on the environmental conditions. Plants from different altitudes are known to be genetically different. Hence, comparison of the plants in any column shows that in a given environment, different genotypes result in different phenotypes. An important inference derived from this experiment is that there is no single genotype that is best in all environments.

The interaction between the genotype and the environment is similarly significant, or even more so, in the case of animals. In one experiment, two strains of rats were selected over many generations; one strain for brightness at finding their way through a maze and the other for dullness ( Fig. 3 ; ref. 39 ). Selection was done in the bright strain by using the brightest rats of each generation to breed the following generation, and in the dull strain by breeding the dullest rats of every generation. After many generations of selection, the descendant bright rats made only about 120 errors running through the maze, whereas dull rats averaged 165 errors. That is a 40% difference. However, the differences between the strains disappeared when rats of both strains were raised in an unfavorable environment of severe deprivation, where both strains averaged 170 errors. The differences also nearly disappeared when the rats were raised with abundant food and other favorable conditions. In this optimal environment, the dull rats reduced their average number of errors from 165 to 120. As with the cinquefoil plants, we see ( i ) that a given genotype gives rise to different phenotypes in different environments and ( ii ) that the differences in phenotype between two genotypes change from one environment to another—the genotype that is best in one environment may not be best in another.

Results of an experiment with two strains of rats: one selected for brightness and the other for dullness. After many generations of selection, when raised in the same environment in which the selection was practiced (normal), bright rats made about 45 fewer errors than dull rats in the maze used for the tests. However, when the rats were raised in an impoverished (restricted) environment, bright and dull rats made the same number of errors. When raised in an abundant (stimulating) environment, the two strains performed nearly equally well. Reprinted with permission from ref. 13 .

Cloning Humans?

In the second half of the 20th century, as dramatic advances were taking place in genetic knowledge, as well as in the genetic technology often referred to as “genetic engineering,” some utopian proposals were advanced, at least as suggestions that should be explored and considered as possibilities, once the technologies had sufficiently progressed. Some proposals suggested that persons of great intellectual or artistic achievement or of great virtue be cloned. If this was accomplished in large numbers, the genetic constitution of mankind would, it was argued, considerably improve.

Such utopian proposals are grossly misguided. It should be apparent that, as stated above, it is not possible to clone a human individual. Seeking to multiply great benefactors of humankind, such as persons of great intelligence or character, we might obtain the likes of Stalin, Hitler, or Bin Laden. As the Nobel Laureate geneticist George W. Beadle asserted many years ago: “Few of us would have advocated preferential multiplication of Hitler’s genes. Yet who can say that in a different cultural context Hitler might not have been one of the truly great leaders of men, or that Einstein might not have been a political villain” ( 8 ). There is no reason whatsoever to expect that the genomes of individuals with excellent attributes would, when cloned, produce individuals similarly endowed with virtue or intelligence. Identical genomes yield, in different environments, individuals who may be quite different. Environments cannot be reproduced, particularly several decades apart, which would be the case when the genotype of the persons selected because of their eminent achievement might be cloned.

Are there circumstances that would justify cloning a person, because he or she wants it? One might think of a couple unable to have children, or a man or woman who does not want to marry, or of two lesbian lovers who want to have a child with the genotype of one in an ovum of the other, or of other special cases that might come to mind ( 40 ). It must be, first, pointed out that the cloning technology has not yet been developed to an extent that would make possible to produce a healthy human individual by cloning. Second, and most important, the individual produced by cloning would be a very different person from the one whose genotype is cloned, as belabored above.

Ethical, social, and religious values will come into play when seeking to decide whether a person might be allowed to be cloned. Most people are likely to disapprove. Indeed, many countries have prohibited human cloning. In 2004, the issue of cloning was raised in several countries where legislatures were also considering whether research on embryonic stem cells should be supported or allowed. The Canadian Parliament on March 12, 2004 passed legislation permitting research with stem cells from embryos under specific conditions, but human cloning was banned, and the sale of sperm and payments to egg donors and surrogate mothers were prohibited. The French Parliament on July 9, 2004 adopted a new bioethics law that allows embryonic stem cell research but considers human cloning a “crime against the human species.” Reproductive cloning experiments would be punishable by up to 20 y in prison. Japan’s Cabinet Council for Science and Technology Policy voted on July 23, 2004 to adopt policy recommendations that would permit the limited cloning of human embryos for scientific research but not the cloning of individuals. On January 14, 2001, the British government amended the Human Fertilization and Embryology Act of 1990 by allowing embryo research on stem cells and allowing therapeutic cloning. The Human Fertilization and Embryology Act of 2008 explicitly prohibited reproductive cloning but allowed experimental stem cell research for treating diabetes, Parkinson’s disease, and Alzheimer’s disease ( 41 , 42 ). On February 3, 2014, the House of Commons voted to legalize a gene therapy technique known as mitochondrial replacement, or three-person in vitro fertilization, in which mitochondria from a donor’s egg cell contribute to a couple’s embryo ( 43 ). In the United States, there are currently no federal laws that ban cloning completely ( 42 ). Thirteen states (Arkansas, California, Connecticut, Iowa, Indiana, Massachusetts, Maryland, Michigan, North Dakota, New Jersey, Rhode Island, South Dakota, and Virginia) ban reproductive cloning, and three states (Arizona, Maryland, and Missouri) prohibit use of public funds for research on reproductive cloning ( 44 ).

Therapeutic Cloning

Cloning of embryonic cells (stem cells) could have important health applications in organ transplantation, treating injured nerve cells, and otherwise. In addition to SCNT, the method discussed above for cloning individuals, another technique is available, induced pluripotent stem cells (iPSCs), although SCNT has proven to be much more effective and less costly. The objective is to obtain pluripotent stem cells that have the potential to differentiate in any of the three germ layers characteristic of humans and other animals: endoderm (lungs and interior lining of stomach and gastrointestinal tract), ectoderm (nervous systems and epidermal tissues), and mesoderm (muscle, blood, bone, and urogenital tissues). Stem cells, with more limited possibilities than pluripotent cells, can also be used for specific therapeutic purposes ( 45 ).

Stem cell therapy consists of cloning embryonic cells to obtain pluripotent or other stem cells that can be used in regenerative medicine, to treat or prevent all sorts of diseases, and for the transplantation of organs. At present, bone marrow transplantation is a widely used form of stem cell therapy; stem blood cells are used in the treatment of sickle cell anemia, a lethal disease when untreated, which is very common in places where malaria is rife because heterozygous individuals are protected against infection by Plasmodium falciparum , the agent of malignant malaria. One of the most promising applications of therapeutic cloning is the growth of organs for transplantation, using stem cells that have the genome of the organ recipient. Two major hurdles would be overcome. One is the possibility of immune rejection; the other is the availability of organs from suitable donors. Another regenerative medical application that might be anticipated is the therapeutic growth of nerve cells. There are hundreds of thousands of individuals throughout the world paralyzed from the neck down and confined for life to a wheelchair as a consequence of damage to the spinal cord below the neck, often as a consequence of a car accident or a fall, that interrupts the transmission of nerve activity from the brain to the rest of the body and vice versa. A small growth of nerve cells sufficient to heal the wound in the spinal cord would have enormous health consequences for the wounded persons and for society.

At present, the one gene therapy modification of the embryo that can be practiced is mitochondrial replacement (MR), legalized in the United Kingdom by the House of Commons on February 3, 2014 ( 43 ), as mentioned earlier. Mutations in the mitochondrial DNA of about 1 in 6,500 individuals account for a variety of severe and often fatal conditions, including blindness, muscular weakness, and heart failure ( 46 ). With MR, the embryo possesses nuclear DNA from the mother and father, as well as mtDNA from a donor female who has healthy mtDNA. However, MR remains technically challenging, with a low rate of success. One complicating issue is that mtDNA replacement is not 100% successful; disease-causing mutant mtDNA persists in the developing embryo and may account for eventual diseases due to heteroplasmy, at least in some tissues. A second issue of concern is that mtDNA disorders often appear late in life. It remains unknown whether the benefits of MR as currently practiced may persist in advanced age.

The author declares no conflict of interest.

This paper results from the Arthur M. Sackler Colloquium of the National Academy of Sciences, “In the Light of Evolution IX: Clonal Reproduction: Alternatives to Sex,” held January 9–10, 2015, at the Arnold and Mabel Beckman Center of the National Academies of Sciences and Engineering in Irvine, CA. The complete program and video recordings of most presentations are available on the NAS website at www.nasonline.org/ILE_IX_Clonal_Reproduction .

This article is a PNAS Direct Submission.

ENCYCLOPEDIC ENTRY

Cloning is a technique scientists use to create exact genetic replicas of genes, cells, or animals.

Biology, Genetics, Health, Chemistry

Cloned Beagles

Two Beagle puppies successfully cloned in Seoul, South Korea. These two dogs were cloned by a biopharmaceutical company that specializes in stem cell based therapeutics.

Photograph by Handout

Cloning is a technique scientists use to make exact genetic copies of living things. Genes , cells, tissues, and even whole animals can all be cloned .

Some clones already exist in nature. Single-celled organisms like bacteria make exact copies of themselves each time they reproduce. In humans, identical twins are similar to clones . They share almost the exact same genes . Identical twins are created when a fertilized egg splits in two.

Scientists also make clones in the lab. They often clone genes in order to study and better understand them. To clone a gene , researchers take DNA from a living creature and insert it into a carrier like bacteria or yeast. Every time that carrier reproduces, a new copy of the gene is made.

Animals are cloned in one of two ways. The first is called embryo twinning. Scientists first split an embryo in half. Those two halves are then placed in a mother’s uterus. Each part of the embryo develops into a unique animal, and the two animals share the same genes . The second method is called somatic cell nuclear transfer. Somatic cells are all the cells that make up an organism, but that are not sperm or egg cells. Sperm and egg cells contain only one set of chromosomes , and when they join during fertilization, the mother’s chromosomes merge with the father’s. Somatic cells , on the other hand, already contain two full sets of chromosomes . To make a clone , scientists transfer the DNA from an animal’s somatic cell into an egg cell that has had its nucleus and DNA removed. The egg develops into an embryo that contains the same genes as the cell donor. Then the embryo is implanted into an adult female’s uterus to grow.

In 1996, Scottish scientists cloned the first animal, a sheep they named Dolly. She was cloned using an udder cell taken from an adult sheep. Since then, scientists have cloned cows, cats, deer, horses, and rabbits. They still have not cloned a human, though. In part, this is because it is difficult to produce a viable clone . In each attempt, there can be genetic mistakes that prevent the clone from surviving. It took scientists 276 attempts to get Dolly right. There are also ethical concerns about cloning a human being.

Researchers can use clones in many ways. An embryo made by cloning can be turned into a stem cell factory. Stem cells are an early form of cells that can grow into many different types of cells and tissues. Scientists can turn them into nerve cells to fix a damaged spinal cord or insulin-making cells to treat diabetes.

The cloning of animals has been used in a number of different applications. Animals have been cloned to have gene mutations that help scientists study diseases that develop in the animals. Livestock like cows and pigs have been cloned to produce more milk or meat. Clones can even “resurrect” a beloved pet that has died. In 2001, a cat named CC was the first pet to be created through cloning. Cloning might one day bring back extinct species like the woolly mammoth or giant panda.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Production Managers

Program specialists, specialist, content production, last updated.

October 19, 2023

User Permissions

For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text on this page is printable and can be used according to our Terms of Service .

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Related Resources

Sciencing_Icons_Science SCIENCE

Sciencing_icons_biology biology, sciencing_icons_cells cells, sciencing_icons_molecular molecular, sciencing_icons_microorganisms microorganisms, sciencing_icons_genetics genetics, sciencing_icons_human body human body, sciencing_icons_ecology ecology, sciencing_icons_chemistry chemistry, sciencing_icons_atomic &amp; molecular structure atomic & molecular structure, sciencing_icons_bonds bonds, sciencing_icons_reactions reactions, sciencing_icons_stoichiometry stoichiometry, sciencing_icons_solutions solutions, sciencing_icons_acids &amp; bases acids & bases, sciencing_icons_thermodynamics thermodynamics, sciencing_icons_organic chemistry organic chemistry, sciencing_icons_physics physics, sciencing_icons_fundamentals-physics fundamentals, sciencing_icons_electronics electronics, sciencing_icons_waves waves, sciencing_icons_energy energy, sciencing_icons_fluid fluid, sciencing_icons_astronomy astronomy, sciencing_icons_geology geology, sciencing_icons_fundamentals-geology fundamentals, sciencing_icons_minerals &amp; rocks minerals & rocks, sciencing_icons_earth scructure earth structure, sciencing_icons_fossils fossils, sciencing_icons_natural disasters natural disasters, sciencing_icons_nature nature, sciencing_icons_ecosystems ecosystems, sciencing_icons_environment environment, sciencing_icons_insects insects, sciencing_icons_plants &amp; mushrooms plants & mushrooms, sciencing_icons_animals animals, sciencing_icons_math math, sciencing_icons_arithmetic arithmetic, sciencing_icons_addition &amp; subtraction addition & subtraction, sciencing_icons_multiplication &amp; division multiplication & division, sciencing_icons_decimals decimals, sciencing_icons_fractions fractions, sciencing_icons_conversions conversions, sciencing_icons_algebra algebra, sciencing_icons_working with units working with units, sciencing_icons_equations &amp; expressions equations & expressions, sciencing_icons_ratios &amp; proportions ratios & proportions, sciencing_icons_inequalities inequalities, sciencing_icons_exponents &amp; logarithms exponents & logarithms, sciencing_icons_factorization factorization, sciencing_icons_functions functions, sciencing_icons_linear equations linear equations, sciencing_icons_graphs graphs, sciencing_icons_quadratics quadratics, sciencing_icons_polynomials polynomials, sciencing_icons_geometry geometry, sciencing_icons_fundamentals-geometry fundamentals, sciencing_icons_cartesian cartesian, sciencing_icons_circles circles, sciencing_icons_solids solids, sciencing_icons_trigonometry trigonometry, sciencing_icons_probability-statistics probability & statistics, sciencing_icons_mean-median-mode mean/median/mode, sciencing_icons_independent-dependent variables independent/dependent variables, sciencing_icons_deviation deviation, sciencing_icons_correlation correlation, sciencing_icons_sampling sampling, sciencing_icons_distributions distributions, sciencing_icons_probability probability, sciencing_icons_calculus calculus, sciencing_icons_differentiation-integration differentiation/integration, sciencing_icons_application application, sciencing_icons_projects projects, sciencing_icons_news news.

• Share Tweet Email Print
• Home ⋅
• Science ⋅
• Biology ⋅
• Molecular Genetics (Biology): An Overview

The Pros & Cons of Cloning

Advantages & Disadvantages of Cloning

As far as anyone really knows, scientists have yet to clone a human being, and there are no federal laws against it in the United State. However, seven states prohibit it altogether, and 10 states only allow it for biomedical research. While more than 30 countries formally ban cloning for reproductive purposes, China, England, Israel, Singapore and Sweden do allow cloning for research, but disallow reproductive cloning.

Cloning Definition

The definition of a clone as explained by Encyclopaedia Britannica is a cell or living thing, an organism, that is "genetically identical to the original cell or organism" from which it comes. The word itself comes from the ancient Greek word "klon," which means twig. Single-cell organisms like some yeasts and bacteria naturally reproduce clones of parent cells via budding or binary fission. Individual body cells within plants and animals are clones that occur during a cell-reproduction process called mitosis.

Cloned Animals

In 2017, scientists in Shanghai succeeded in cloning two genetically identical long-tailed macaques, small brown and black monkeys with body lengths of 16 to 28 inches. The last successful cloning of a primate was in 1998, but scientists have also cloned about 20 different types of animals including dogs, pigs, frogs, mice, cows and rabbits since the first cloned animal in 1996.

The First Cloned Animal: Dolly the Sheep

The first successful animal cloning occurred over 22 years ago, after a Scottish Blackface sheep surrogate mother gave birth to Dolly on July 5, 1996, at the Roslin Institute, part of the University of Edinburgh. Cloned from a six-year-old Dorset sheep, scientists analyzed her DNA at her first birthday and discovered that the telomeres at the end of her DNA strands (think eraser on a pencil head) were shorter that they should be for her age. As animals and humans age, these telomeres become shorter. The average age for sheep runs between six to 12 years. Dolly died when she was six, and though she had shortened telomeres, she lived an average life and produced multiple offspring through natural methods, but she also developed diseases in her later years.

Human Cloning Pros and Cons

The pros or advantages of human cloning include:

• ​ Infertility: ​ Infertile people or same-sex couples could have children made from cloned cells.
• ​ Organ replacement: ​ A clone, like in the movie, "The Island," could be a source for transplant organs or tissue. (There are ethical issues that arise from this, however.)
• ​ Genetic research: ​ Cell cloning could assist scientists in gene editing and research.
• ​ Selective human traits: ​ After editing or removing bad genes, cloning could lead engineered humans for specific traits.
• ​ Human development: ​ Cloning could enhance and advance human development.

The cons or disadvantages of human cloning raise moral, ethical and safety issues:

• ​ Reproductive cloning: ​ The negatives of human cloning including the making of designer babies.
• ​ Human cloning: ​ Could be a violation of the clone's individual human rights.
• ​ Embryonic cloning: ​ Cellular degradation occurs when too many clones are made from embryos.
• ​ Unique identities: ​ Cloning raises the question of a moral or human right to an exclusive identity.
• ​ Societal impacts: ​ Human cloning could produce psychological distress for the clone and society.

Effects of Cloning

While the purpose of cloning is to create an exact replica – if scientists cloned a human that appears identical to the original – it raises the questions as to whether the cloned human is an individual separate from the original and is due the same rights as any other human. Human cloning research and techniques could subject the clone to unacceptable risks such as a shortened life, bad health or other unknown problems. In the end, legalizing cloning on a wide-scale basis could lead to a disrespect for human life and the individual worth of a person, which might ultimately diminish all humans in the end.

Related Articles

Who invented cloning & when, gene editing is not about making designer babies, what makes dna fingerprinting unique, pros & cons of cloning plants & animals, pros and cons of recombinant dna technology, ethics research paper topics, a list of five characteristics of chromosomes, the importance of studying human dna genetics, how to write a notation of a karyotype, when is a mutation in a dna molecule passed to offspring, difference between recombinant dna & genetic engineering, how do i compare frankenstein & cloning, what are the differences between pcr and cloning, the production of recombinant human growth hormones..., what is embryo cloning, four major types of chromosomes, the differences in fraternal & paternal twins, recombinant dna technology for vaccine development, how are genes on sex chromosomes inherited.

• CNN: Monkey See, Monkey 2: Scientists Clone Monkeys Using Technique That Created Dolly the Sheep
• Encyclopaedia Britannica: Macaque
• The University of Edinburgh: The Life of Dolly
• North Carolina State Extension: Sheep Facts
• Georgetown University: Cloning Human Beings
• Johns Hopkins University: Ask an Expert: How Close Are We to Cloning Humans?
• The New Atlantis: Appendix: State Laws on Human Cloning
• Encyclopaedia Britannica: Clone

About the Author

As a journalist and editor for several years, Laurie Brenner has covered many topics in her writings, but science is one of her first loves. Her stint as Manager of the California State Mining and Mineral Museum in California's gold country served to deepen her interest in science which she now fulfills by writing for online science websites. Brenner is also a published sci-fi author. She graduated from San Diego's Coleman College in 1972.

Find Your Next Great Science Fair Project! GO

We Have More Great Sciencing Articles!

• Essay Samples
• College Essay
• Writing Tools
• Writing guide

↑ Return to College Essay

Essay: An Introduction to Cloning

The National Human Genome Research Institute describes cloning as, “processes that can be used to produce genetically identical copies of a biological entity.” The result is called a clone and the practice of cloning living things has raised a lot of controversy over the years. In the lab, scientists have successfully cloned cells, genes and even a sheep. But is it a good idea?

Natural Cloning

Cloning occurs naturally in some cases. That includes living organisms, such as bacteria, that split and clone on their own. Cloning also occurs in organisms that reproduce using asexual reproduction. Identical twins are also considered clones, as the original cell “copies” itself and produces another human being or animal.

Artificial Cloning

Artificial cloning can be done using one of three processes – therapeutic cloning, gene cloning or reproductive cloning. Therapeutic cloning involves creating new tissue to replace injured or dead tissue. Gene cloning creates new copies of specific genes or segments of DNA. Reproductive cloning is when an entire organism is cloned, and is also what most people think of when they hear about cloning.

How is Cloning Done?

Artificial cloning is done by scientists and involves taking a gene from one organism and inserting it into the genetic material of another carrier organism. The combination of material is then placed in a safe area and allowed to clone, which occurs as the materials copy themselves over and over again.

In the case of reproductive cloning, when an entire animal is cloned, the process is a bit different. First, scientists remove a somatic cell from the original animal. This often comes from the animal’s skin. The DNA from that cell is transferred to an egg cell that has had its DNA material taken out. The egg is then able to become an embryo that is later implanted into the womb of an adult female animal. The female then gives birth to the clone. The most famous instance of this type of cloning was Dolly the sheep. Human Cloning

Despite what people have heard, human cloning is not something that is even close to happening. There is no evidence that any scientist or research facility has ever successfully cloned a human being. While there are some groups claiming to have cloned a human, the clone never reached the birthing stage. According to experts, it would be nearly impossible to clone a human as one of the proteins needed for the process is too close to a human cell’s chromosomes and removing the DNA without also damaging those proteins is very difficult to do.

Benefits of Cloning

It might sound like something out of a science fiction movie, but there are scientific benefits to cloning certain animals. By doing so, researchers are able to learn more about the animal, which can be beneficial to agriculture. When the FDA approved cloned material for human consumption, entities that raise animals for meat or milk were able to begin producing on the best meat and milk, though doing so costs more, which means that consumers would have to pay more.

Another possible benefit to cloning is to rebuild endangered species before they become extinct. By cloning these animals, their numbers could be increased, something that ensures that the stability of an ecosystem isn’t compromised. People across the world have also driven research into cloning beloved pets.

Drawbacks of Cloning

One of the biggest problems with cloning is that the clone isn’t always healthy enough to live and using clones to rebuild a species results in a lack of the variability needed for a species’s survival. Cloning adult animals means that the clone is born with “older” DNA, which shortens its lifespan.

Cloning continues to be a hot topic that is debated all over the world. What side are you on?

Follow Us on Social Media

Get more free essays

Send via email

Most useful resources for students:.

• Free Essays Download
• Writing Tools List
• Proofreading Services
• Universities Rating

Contributors Bio

Find more useful services for students

Free plagiarism check, professional editing, online tutoring, free grammar check.

Ethical Debate on Human Cloning Essay

Introduction, unethical issues about cloning, ethical issues, works cited.

Cloning refers to the scientific multiplication and production of new cells to reproduce individuals that resemble their natural counterparts (Craig 3). It involves the duplication and modification of reproductive genes from different individuals to produce individuals that resemble their parents. This essay explores the issues raised by opponents and proponents of this scientific discovery.

Every person deserves the right and freedom to be respected and valued as a human being. Nobody is supposed to discriminate against others because of their origin since all people are equal they were all born of a father and mother and went through the same process before they came to this world (Brown 14). However, cloning is a disrespectful scientific innovation that ignores the natural ways of raising families. In addition, it discredits the process of preproduction that involves having sexual affairs, conception, pregnancy and delivery. Cloned individuals will not have the dignity given to human beings born through natural means.

Secondly, this activity is very inhumane since it involves the destruction of fertile human cells. Human beings are not supposed to be used as specimens for laboratory activities. However, since this experiment cannot be used using other animals; as a result, scientists must look for cells from human beings. This process disrespects human value since it depicts people as specimens (Craig 7). A previous experiment conducted to clone a sheep led to the destruction of more than 270 cells. The result led to only one sheep conceiving even though there were more than ten sheep. This reveals how this process will lead to damages and unnecessary expenses.

Thirdly, natural selection places individuals at extreme ends regarding survival in the future. Natural reproduction ensures individuals produced can withstand all-natural challenges that pose serious risks to their existence (Brown 33). The cloning of Dolly did not give any future expectations and happenings that may interfere with its life. Therefore, this process is more of guesswork than a confident undertaking.

Lastly, this process transgresses societal expectations and exposes people to mechanical activities. There is no way they can rely on scientific innovations to bring up children when they have the same ability (Macintosh 121). Religious teachings regard their supreme being to be in charge of creation. When people create life this is perceived to be challenging nature; therefore, this is an antisocial activity that must be stopped.

Proponents of cloning suggest that this activity enables help, sick people, to get remedies for their complications (Mitchell 56). Cell division and multiplication has enabled doctors to perform successful organ transplants. Therefore, many lives have been saved courtesy of cloning.

Secondly, they argue that this activity will produce individuals of high quality that will be useful in various industrial activities. They will offer a cheap and reliable supply of labor (Kass 76). These proponents insist that cloning will lead to the production of individuals that are resistant to diseases, have a long lifespan and can adjust to various environmental challenges.

Lastly, they are persuaded that successful human cloning procedures will be applied in other fields like agriculture to ensure they produce quality individuals. This practice will be applied in other fields that lack quality individuals to perform various tasks.

Human beings deserve to live a quality life and scientific innovations are providing various ways of improving society to meet human needs. However, cloning is not an alternative to the challenges facing human beings. People are can reproduce without this scientific intervention that is coupled with serious challenges. Therefore, cloning is an unethical issue and it should be banned to avoid exposing human beings to the risks mentioned above.

Brown, Thomas. Gene Cloning and DNA Analysis: An Introduction. New York: Willey-Blackwell, 2010. Print.

Craig, Robin. Cloning Around: The Ethics of Human Cloning and Stem Cell Research. Basingstoke: Palgrave, 2012. Print.

Kass, Leon. Human Cloning and Human Dignity: The Report of the President’s Council on Bioethics. New York: PublicAffairs, 2010. Print.

Macintosh, Kerry. Human Cloning: Four Fallacies and their Legal Consequences. Cambridge Bioethics and Law. Cambridge: Cambridge University Press, 2012. Print.

Mitchell, Winnie. Cloning Terror: The War of Images, 9/11 to the Present. Chicago: University of Chicago Press, 2011. Print.

• Chicago (A-D)
• Chicago (N-B)

IvyPanda. (2022, April 9). Ethical Debate on Human Cloning. https://ivypanda.com/essays/ethical-debate-on-human-cloning/

"Ethical Debate on Human Cloning." IvyPanda , 9 Apr. 2022, ivypanda.com/essays/ethical-debate-on-human-cloning/.

IvyPanda . (2022) 'Ethical Debate on Human Cloning'. 9 April.

IvyPanda . 2022. "Ethical Debate on Human Cloning." April 9, 2022. https://ivypanda.com/essays/ethical-debate-on-human-cloning/.

1. IvyPanda . "Ethical Debate on Human Cloning." April 9, 2022. https://ivypanda.com/essays/ethical-debate-on-human-cloning/.

Bibliography

IvyPanda . "Ethical Debate on Human Cloning." April 9, 2022. https://ivypanda.com/essays/ethical-debate-on-human-cloning/.

• Ethics of Cloning
• Whether or Not Human Cloning Should Be Allowed
• The Moral Case Against Cloning-for-Biomedical-Research
• The Cloning Controversy
• Ethical Issues on Human Therapeutic and Reproductive Cloning
• Cloning and the Principles That Should Regulate It
• Molecular, Cell and Organism Cloning Techniques
• The New Advancements in Cloning and the Ethical Debate Surrounding It
• Controversies in Therapeutic Cloning
• Animal Cloning Benefits and Controversies
• The Nursing Practices, From XVI Century to Present Days
• Nurses’ Conduct a Community Assessment of the Dade County in Miami
• Conflicts Between Nursing Ethics and Law
• Conflicts Between Ethics and the Law in Healthcare
• Disclosure of a Physician’s HIV Status

• Introduction to Genomics
• Educational Resources
• Policy Issues in Genomics
• The Human Genome Project
• Funding Opportunities
• Funded Programs & Projects
• Division and Program Directors
• Scientific Program Analysts
• Contact by Research Area
• News & Events
• Research Areas
• Research investigators
• Research Projects
• Clinical Research
• Data Tools & Resources
• Genomics & Medicine
• Family Health History
• For Patients & Families
• For Health Professionals
• Jobs at NHGRI
• Training at NHGRI
• Funding for Research Training
• Professional Development Programs
• NHGRI Culture
• Social Media
• Broadcast Media
• Image Gallery
• Press Resources
• Organization
• NHGRI Director
• Mission & Vision
• Policies & Guidance
• Institute Advisors
• Strategic Vision
• Leadership Initiatives
• Diversity, Equity, and Inclusion
• Partner with NHGRI
• Staff Search

Cloning Fact Sheet

The term cloning describes a number of different processes that can be used to produce genetically identical copies of a biological entity. The copied material, which has the same genetic makeup as the original, is referred to as a clone. Researchers have cloned a wide range of biological materials, including genes, cells, tissues and even entire organisms, such as a sheep.

Do clones ever occur naturally?

Yes. In nature, some plants and single-celled organisms, such as bacteria , produce genetically identical offspring through a process called asexual reproduction. In asexual reproduction, a new individual is generated from a copy of a single cell from the parent organism.

Natural clones, also known as identical twins, occur in humans and other mammals. These twins are produced when a fertilized egg splits, creating two or more embryos that carry almost identical DNA . Identical twins have nearly the same genetic makeup as each other, but they are genetically different from either parent.

What are the types of artificial cloning?

There are three different types of artificial cloning: gene cloning, reproductive cloning and therapeutic cloning.

Gene cloning produces copies of genes or segments of DNA. Reproductive cloning produces copies of whole animals. Therapeutic cloning produces embryonic stem cells for experiments aimed at creating tissues to replace injured or diseased tissues.

Gene cloning, also known as DNA cloning, is a very different process from reproductive and therapeutic cloning. Reproductive and therapeutic cloning share many of the same techniques, but are done for different purposes.

What sort of cloning research is going on at NHGRI?

Gene cloning is the most common type of cloning done by researchers at NHGRI. NHGRI researchers have not cloned any mammals and NHGRI does not clone humans.

How are genes cloned?

Researchers routinely use cloning techniques to make copies of genes that they wish to study. The procedure consists of inserting a gene from one organism, often referred to as "foreign DNA," into the genetic material of a carrier called a vector. Examples of vectors include bacteria, yeast cells, viruses or plasmids, which are small DNA circles carried by bacteria. After the gene is inserted, the vector is placed in laboratory conditions that prompt it to multiply, resulting in the gene being copied many times over.

How are animals cloned?

In reproductive cloning, researchers remove a mature somatic cell , such as a skin cell, from an animal that they wish to copy. They then transfer the DNA of the donor animal's somatic cell into an egg cell, or oocyte, that has had its own DNA-containing nucleus removed.

Researchers can add the DNA from the somatic cell to the empty egg in two different ways. In the first method, they remove the DNA-containing nucleus of the somatic cell with a needle and inject it into the empty egg. In the second approach, they use an electrical current to fuse the entire somatic cell with the empty egg.

In both processes, the egg is allowed to develop into an early-stage embryo in the test-tube and then is implanted into the womb of an adult female animal.

Ultimately, the adult female gives birth to an animal that has the same genetic make up as the animal that donated the somatic cell. This young animal is referred to as a clone. Reproductive cloning may require the use of a surrogate mother to allow development of the cloned embryo, as was the case for the most famous cloned organism, Dolly the sheep.

What animals have been cloned?

Over the last 50 years, scientists have conducted cloning experiments in a wide range of animals using a variety of techniques. In 1979, researchers produced the first genetically identical mice by splitting mouse embryos in the test tube and then implanting the resulting embryos into the wombs of adult female mice. Shortly after that, researchers produced the first genetically identical cows, sheep and chickens by transferring the nucleus of a cell taken from an early embryo into an egg that had been emptied of its nucleus.

It was not until 1996, however, that researchers succeeded in cloning the first mammal from a mature (somatic) cell taken from an adult animal. After 276 attempts, Scottish researchers finally produced Dolly, the lamb from the udder cell of a 6-year-old sheep. Two years later, researchers in Japan cloned eight calves from a single cow, but only four survived.

Besides cattle and sheep, other mammals that have been cloned from somatic cells include: cat, deer, dog, horse, mule, ox, rabbit and rat. In addition, a rhesus monkey has been cloned by embryo splitting.

Have humans been cloned?

Despite several highly publicized claims, human cloning still appears to be fiction. There currently is no solid scientific evidence that anyone has cloned human embryos.

In 1998, scientists in South Korea claimed to have successfully cloned a human embryo, but said the experiment was interrupted very early when the clone was just a group of four cells. In 2002, Clonaid, part of a religious group that believes humans were created by extraterrestrials, held a news conference to announce the birth of what it claimed to be the first cloned human, a girl named Eve. However, despite repeated requests by the research community and the news media, Clonaid never provided any evidence to confirm the existence of this clone or the other 12 human clones it purportedly created.

In 2004, a group led by Woo-Suk Hwang of Seoul National University in South Korea published a paper in the journal Science in which it claimed to have created a cloned human embryo in a test tube. However, an independent scientific committee later found no proof to support the claim and, in January 2006, Science announced that Hwang's paper had been retracted.

From a technical perspective, cloning humans and other primates is more difficult than in other mammals. One reason is that two proteins essential to cell division, known as spindle proteins, are located very close to the chromosomes in primate eggs. Consequently, removal of the egg's nucleus to make room for the donor nucleus also removes the spindle proteins, interfering with cell division. In other mammals, such as cats, rabbits and mice, the two spindle proteins are spread throughout the egg. So, removal of the egg's nucleus does not result in loss of spindle proteins. In addition, some dyes and the ultraviolet light used to remove the egg's nucleus can damage the primate cell and prevent it from growing.

Do cloned animals always look identical?

No. Clones do not always look identical. Although clones share the same genetic material, the environment also plays a big role in how an organism turns out.

For example, the first cat to be cloned, named Cc, is a female calico cat that looks very different from her mother. The explanation for the difference is that the color and pattern of the coats of cats cannot be attributed exclusively to genes. A biological phenomenon involving inactivation of the X chromosome (See sex chromosome ) in every cell of the female cat (which has two X chromosomes) determines which coat color genes are switched off and which are switched on. The distribution of X inactivation, which seems to occur randomly, determines the appearance of the cat's coat.

What are the potential applications of cloned animals?

Reproductive cloning may enable researchers to make copies of animals with the potential benefits for the fields of medicine and agriculture.

For instance, the same Scottish researchers who cloned Dolly have cloned other sheep that have been genetically modified to produce milk that contains a human protein essential for blood clotting. The hope is that someday this protein can be purified from the milk and given to humans whose blood does not clot properly. Another possible use of cloned animals is for testing new drugs and treatment strategies. The great advantage of using cloned animals for drug testing is that they are all genetically identical, which means their responses to the drugs should be uniform rather than variable as seen in animals with different genetic make-ups.

After consulting with many independent scientists and experts in cloning, the U.S. Food and Drug Administration (FDA) decided in January 2008 that meat and milk from cloned animals, such as cattle, pigs and goats, are as safe as those from non-cloned animals. The FDA action means that researchers are now free to using cloning methods to make copies of animals with desirable agricultural traits, such as high milk production or lean meat. However, because cloning is still very expensive, it will likely take many years until food products from cloned animals actually appear in supermarkets.

Another application is to create clones to build populations of endangered, or possibly even extinct, species of animals. In 2001, researchers produced the first clone of an endangered species: a type of Asian ox known as a guar. Sadly, the baby guar, which had developed inside a surrogate cow mother, died just a few days after its birth. In 2003, another endangered type of ox, called the Banteg, was successfully cloned. Soon after, three African wildcats were cloned using frozen embryos as a source of DNA. Although some experts think cloning can save many species that would otherwise disappear, others argue that cloning produces a population of genetically identical individuals that lack the genetic variability necessary for species survival.

Some people also have expressed interest in having their deceased pets cloned in the hope of getting a similar animal to replace the dead one. But as shown by Cc the cloned cat, a clone may not turn out exactly like the original pet whose DNA was used to make the clone.

What are the potential drawbacks of cloning animals?

Reproductive cloning is a very inefficient technique and most cloned animal embryos cannot develop into healthy individuals. For instance, Dolly was the only clone to be born live out of a total of 277 cloned embryos. This very low efficiency, combined with safety concerns, presents a serious obstacle to the application of reproductive cloning.

Researchers have observed some adverse health effects in sheep and other mammals that have been cloned. These include an increase in birth size and a variety of defects in vital organs, such as the liver, brain and heart. Other consequences include premature aging and problems with the immune system. Another potential problem centers on the relative age of the cloned cell's chromosomes. As cells go through their normal rounds of division, the tips of the chromosomes, called telomeres, shrink. Over time, the telomeres become so short that the cell can no longer divide and, consequently, the cell dies. This is part of the natural aging process that seems to happen in all cell types. As a consequence, clones created from a cell taken from an adult might have chromosomes that are already shorter than normal, which may condemn the clones' cells to a shorter life span. Indeed, Dolly, who was cloned from the cell of a 6-year-old sheep, had chromosomes that were shorter than those of other sheep her age. Dolly died when she was six years old, about half the average sheep's 12-year lifespan.

What is therapeutic cloning?

Therapeutic cloning involves creating a cloned embryo for the sole purpose of producing embryonic stem cells with the same DNA as the donor cell. These stem cells can be used in experiments aimed at understanding disease and developing new treatments for disease. To date, there is no evidence that human embryos have been produced for therapeutic cloning.

The richest source of embryonic stem cells is tissue formed during the first five days after the egg has started to divide. At this stage of development, called the blastocyst, the embryo consists of a cluster of about 100 cells that can become any cell type. Stem cells are harvested from cloned embryos at this stage of development, resulting in destruction of the embryo while it is still in the test tube.

What are the potential applications of therapeutic cloning?

Researchers hope to use embryonic stem cells, which have the unique ability to generate virtually all types of cells in an organism, to grow healthy tissues in the laboratory that can be used replace injured or diseased tissues. In addition, it may be possible to learn more about the molecular causes of disease by studying embryonic stem cell lines from cloned embryos derived from the cells of animals or humans with different diseases. Finally, differentiated tissues derived from ES cells are excellent tools to test new therapeutic drugs.

What are the potential drawbacks of therapeutic cloning?

Many researchers think it is worthwhile to explore the use of embryonic stem cells as a path for treating human diseases. However, some experts are concerned about the striking similarities between stem cells and cancer cells. Both cell types have the ability to proliferate indefinitely and some studies show that after 60 cycles of cell division, stem cells can accumulate mutations that could lead to cancer. Therefore, the relationship between stem cells and cancer cells needs to be more clearly understood if stem cells are to be used to treat human disease.

What are some of the ethical issues related to cloning?

Gene cloning is a carefully regulated technique that is largely accepted today and used routinely in many labs worldwide. However, both reproductive and therapeutic cloning raise important ethical issues, especially as related to the potential use of these techniques in humans.

Reproductive cloning would present the potential of creating a human that is genetically identical to another person who has previously existed or who still exists. This may conflict with long-standing religious and societal values about human dignity, possibly infringing upon principles of individual freedom, identity and autonomy. However, some argue that reproductive cloning could help sterile couples fulfill their dream of parenthood. Others see human cloning as a way to avoid passing on a deleterious gene that runs in the family without having to undergo embryo screening or embryo selection.

Therapeutic cloning, while offering the potential for treating humans suffering from disease or injury, would require the destruction of human embryos in the test tube. Consequently, opponents argue that using this technique to collect embryonic stem cells is wrong, regardless of whether such cells are used to benefit sick or injured people.

Last updated: August 15, 2020