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Human Cloning and Human Dignity:
An Ethical Inquiry

Table of Contents

The President's Council on Bioethics
Washington, D.C.
July 2002

Chapter One

The Meaning of Human Cloning: An Overview

The prospect of human cloningi burst into the public consciousness in 1997, following the announcement of the successful cloning of Dolly the sheep. It has since captured much attention and generated great debate, both in the United States and around the world. Many are repelled by the idea of producing children who would be genetically virtually identical to pre-existing individuals, and believe such a practice unethical. But some see in such cloning the possibility to do good for infertile couples and the broader society. Some want to outlaw it, and many nations have done so. Others believe the benefits outweigh the risks and the moral concerns, or they oppose legislative interference with science and technology in the name of freedom and progress.

Complicating the national dialogue about human cloning is the isolation in 1998 of human embryonic stem cells, which many scientists believe to hold great promise for understanding and treating many chronic diseases and conditions. Some scientists also believe that stem cells derived from cloned human embryos, produced explicitly for such research, might prove to be uniquely useful for studying many genetic diseases and devising novel therapies. Public reaction to this prospect has been mixed, with some Americans supporting it in the hope of advancing biomedical research and helping the sick and the suffering, while others are concerned about the instrumentalization or abuse of nascent human life and the resulting danger of moral insensitivity and degradation.

In the United States, several attempts have been made to initiate a comprehensive public review of the significance of human cloning and to formulate appropriate policies. Most notably, the National Bioethics Advisory Commission (NBAC) released a report on the subject of cloning-to-produce-children in 1997.ii The Commission concluded that cloning-to-produce-children was, at least for the time being, unethical on safety grounds, and that the deeper and more permanent moral concerns surrounding the practice should be the subject of continuing deliberation "in order to further our understanding of the ethical and social implications of this technology and to enable society to produce appropriate long-term policies regarding this technology" (p. 106).

In this report, the President's Council on Bioethics takes up this important charge, and considers the ethical and social implications of human cloning (both for producing children and for biomedical research) in their full scope, with the aim of informing public policy on the matter.

Our work toward this end is guided by a number of explicit methodological choices about modes of approach, points of departure, and spirit of inquiry. We locate human cloning within its larger human and technological context, rather than consider it in isolation. We focus first on the broad human goods that it may serve or threaten, rather than on the immediate impact of the technique itself. And we present the strongest arguments for the relevant moral and policy positions, rather than frame the arguments in order to seek consensus. By our broad approach, our starting on the plane of human goods, and our open spirit of inquiry, we hope to contribute to a richer and deeper understanding of what human cloning entails, how we should think about it, and what we should do about it.

Two points of clarification before we proceed. First, all of our considerations and arguments assume that cloning techniques, both for producing children and for providing embryos useful in biomedical research, could succeed in human beings as they have with other mammals. Cloning-to-produce-children has never been successfully carried out in humans, and cloning embryos for biomedical research has not progressed beyond the earliest experiments. We consider it part of our task to judge whether even attempts at human cloning would be ethical or should be lawful. To conduct the analysis and assessment needed for such judgment, we necessarily proceed on the assumption, which we believe is supported by evidence from animal experiments, that human cloning is indeed a possibility – that sooner or later, if it were allowed and attempted, human cloning could be successfully carried out. Practically all public discussion of the ethics of human cloning has, whether expressly or not, proceeded on this same premise, and rightly so.

Second, on some of the matters discussed in this report, Members of the Council are not of one mind. Given that competing goods are at stake, and different people regard them differently, this is not at all surprising. Rather than bury these differences in search of a spurious consensus, we have sought to present all views fairly and fully. Yet transcending these differences is a more fundamental agreement about the worthiness of the approach we have adopted and the arguments we have made. Accordingly, the Council is unanimous in owning the entire report and in recommending, to all, the report's discussions and arguments for serious consideration.

In the remainder of this overview, we describe the context of human cloning and the discussions it has generated. In the course of doing so, we identify the kinds of questions and concerns that would permit a full assessment of the meaning of human cloning. These questions and concerns will guide us throughout the report.

Human Cloning in Context

It is useful to begin by observing how it is that the question of human cloning has come before us. The prospect of cloning human beings confronts us now not as the result of a strong public demand or a long-standing need. Unlike sought-for medical therapies, it was not at the outset pursued as a cure for disease. Neither has it been sought explicitly as a tool for genetic control or "enhancement" of human offspring. Cloning has arisen not so much because it was actively sought for its own sake, but because it is a natural extension of certain biotechnological advances of the past several decades.iii

For more than half a century, and at an accelerating pace, biomedical scientists have been gaining wondrous new knowledge of the workings of living beings, from small to great. Increasingly, they also are providing precise and sophisticated knowledge of the workings of the human body and mind. Such knowledge of how things work often leads to new technological powers to control or alter these workings, powers ordinarily sought in order to treat human disease and relieve suffering.

Questions regarding the meaning of acquiring such powers – both the promise and the peril – have attracted scholarly and public attention. For more than thirty years, ethical issues related to biomedical advance have occupied the growing field of bioethics. Increasingly, these ethical issues have spawned public discussion and debates. A growing number of people sense that something new and momentous is happening; that the accelerating waves of biotechnical advances touch deeply on our most human concerns; and that the centuries-old project for human mastery of nature may now be, so to speak, coming home, giving humanity the power to alter and "master" itself.

One important aspect of human life already affected by new biotechnologies is human reproduction. For several decades now, building on advances in genetics, cell biology, and developmental biology, and on technologies used first in animal husbandry, scientists around the world have been adapting techniques and developing tools to study, influence, and manipulate the origins of human life. Beginning with techniques of artificial insemination and progressing through in vitro fertilization (IVF) and intracytoplasmic sperm injection, artificial aids to reproduction have come into standard medical use.

Cloning is, in one sense, another step along this path. It developed as the result of research into mammalian reproduction and development, where it is desired also as a means of replicating animals especially useful to human beings. It is also proposed as an additional means to overcome infertility in humans.

But the controversy surrounding human cloning, and the widespread sense of disquiet and concern with which the prospect has been received around the world, make it clear that cloning is not just another reproductive technology, to be easily assimilated into ordinary life. Nearly all participants in the public debate over human cloning appear to agree that the subject touches upon some of the most fundamental questions regarding the nature of our humanity and the character of our society. In addition, it raises questions about the aims of biomedical science and about the relation between science and society, including the possibility and desirability of exercising public control over the uses of biomedical technology and the conduct of biomedical research. It is because we sense these larger entailments that the subject of cloning matters so much to us. It is these considerations that give the present debate its force and prominence. Thus only through a serious reflection on these broader questions can the full meaning of human cloning be discovered. The prospect of human cloning may have been brought before us by the march of biotechnology, but now that it is here it is incumbent upon us to look well beyond its technical and medical aspects, if we are to appreciate its significance in full.

Three areas of inquiry in particular seem essential to any understanding of the full meaning of human cloning: the nature and meaning of human procreation; the aims, ends, and means of biomedical science and technology; and the relation of science and technology to the larger society.

Cloning and Human Procreation

Human procreation provides the major context for considering the prospect of cloning, especially cloning-to-produce-children. Much of the time, most of us tend to take for granted this central aspect of human life, through which all of us come to be and through which we give birth to our posterity. But the prospect of creating children by cloning brings this subject sharply before us and compels us to examine the nature and meaning of human procreation. For cloning-to-produce-children, while it may be a potential aid to human reproduction, appears also to be a substitute for it, or at least for its natural, un-programmed, sexual character. Properly to assess the meaning of producing cloned children, one must first of all consider the meaning of human procreation in all its aspects and entailments.iv

Human procreation, though seemingly an exclusively private act, has a profoundly public meaning. It determines the relations between one generation and the next, shapes identities, creates attachments, and sets up responsibilities for the care and rearing of children (and the care of aging parents or other needy kin). Thus, in considering proposals to clone children, we must ask ourselves what cloning would mean not only for the individual parents and children involved, but also for the surrounding families and for all of society. Opinions on this subject will of course differ, sometimes widely, as they rest on possibly differing perceptions of human procreation and family life. Yet the following basic observations, concerns, and questions seem pertinent, notwithstanding possible differences of opinion among us about how much weight to give them.

Among the important aspects of the topic are these: the meaning of having children; the meaning of sexual, as opposed to asexual, reproduction; the meaning of origins and genetic endowment for identity and sense of self; the meaning of exercising greater human control over the processes and "products" of human reproduction; and the difference between begetting and making.

To understand what it would mean to clone a child, we do well to consider most generally what it means to bring a child into the world, and with what attitude we should regard his or her arrival and presence. Our children are, to begin with, our replacements, those who will one day stand in our place. They are, as Hans Jonas has remarked, "life's own answer to mortality." Though their conception is the fruit of our activity, and though we are responsible for saying "yes" to their arrival, we do not, in normal procreation, command their conception, control their makeup, or rule over their development and birth. They are, in an important sense, "given" to us. Though they are our children, they are not our property. Though they are our flesh and blood, and deeply kin, they are also independent "strangers" who arrive suddenly out of the darkness and whom we must struggle to get to know. Though we may seek to have them for our own self-fulfillment, they exist also and especially for their own sakes. Though we seek to educate them, they are not like our other projects, determined strictly according to our plans and serving only our desires.

If these observations are correct, certain things follow regarding the attitudes we should have toward our children. We treat them rightly when we treat them as gifts rather than as products, and when we treat them as independent beings whom we are duty-bound to protect and nurture rather than as extensions of ourselves subject only to our wills and whims. Might these attitudes toward children be altered by cloning, and, if so, how? Would social attitudes toward children change, even if cloning were not practiced widely? What might these changes mean?

To understand how the introduction of asexual reproduction might affect human life, we must first seek the intrinsic meaning of the sexual character of human reproduction and what it implies for individuals, for families, and for the relation between the generations. Once again, the following observations – while hardly exhaustive – seem pertinent and important.

In sexual reproduction,v each child has two complementary biological progenitors. Each child thus stems from and unites exactly two lineages, lines that trace backward in similar branching fashion for ages. Moreover, the precise genetic endowment of each child is determined by a combination of nature and chance, not by human design: each human child naturally acquires and shares the common human species genotype, each child is genetically (equally) kin to each (both) parent(s), yet each child is also genetically Cloning-to-produce-children departs from this pattern. A cloned child has unilineal, not bilineal, descent; he or she is genetically kin to only one progenitor. What is more, the genetic kinship is near-total: the cloned child is not genetically unique, but shares almost completely the genetic endowment of the "original" progenitor. Finally, this endowment comes to the cloned child not by chance but by human choice and decision. What do these differences mean for the cloned child, for family relations, and for relations across the generations?

Origins and genetic endowment are significant aspects of who one is and how one regards oneself, of one's "identity," individuality, and place in the social order. The biological linkages and prospects implicit in sexual reproduction help to define us, though, it should go without saying, they do not define us completely. While we are more "what we choose to become" than we are "where we came from," our human beginnings matter, biologically, psychically, and socially. Because of the way we are generated, each of us is at once (1) equally human, (2) equally marked by and from birth as mortal, (3) equally enmeshed in a particular familial nexus of origin, (4) equally individuated in our trajectory from the beginning to the end of our lives – and, if all goes well, (5) equally capable (despite our mortality) of participating with a complementary other in the very same renewal of human possibility through procreation. Our genetic identity – manifest, for instance, in our distinctive appearance by which we are recognized by others and in our immune system by which we maintain our integrity against "foreign invasions" – also symbolizes and foreshadows exactly the unique, never-to-be-repeated character of each human life. In addition, human societies virtually everywhere have structured child-rearing responsibilities and systems of identity and relationships on the bases of these natural facts of begetting. Kinship is tied to origins, and identity, at least in part, is tied to kinship. It is against this background that we must consider the implications of clonal reproduction, and the alterations it might produce in how cloned children would regard themselves and how they would be regarded by others. What would cloning-to-produce-children mean for individual identity, for kinship, and for sense of self, not only for the cloned child but also for his or her family?

Unaided sexual procreation is an activity at once natural, private, mysterious, unmediated, unpredictable, and undesigned. With the arrival of techniques such as IVF to assist procreation in the face of infertility, the process becomes less private and more mediated. But although technique is used, the basic structure of sexual reproduction – the combination of genetic material from father and mother resulting in a genetically unique child – is unaltered, the outcome is still unpredictable, and the genetic endowment of the child remains uncontrolled and undesigned. Cloning-to-produce-children would seem to bring procreation under human control and direction. What would this mean? What are the implications of allowing reproductive activities to become increasingly technological and commercialized? Cloning would be the first instance in which parents could select in advance the precise (or nearly precise) genetic makeup of their child, by selecting the donor to be cloned. It therefore forces us to ask what might be the difference between begetting and making, to wonder whether cloning somehow crosses the line between them, and, if so, to consider whether and why that should worry us.

Though admittedly sketchy and incomplete, these preliminary reflections on the nature and meaning of human procreation should enable us to see cloning – and especially cloning-to-produce-children-in its most important human context and to understand its deepest implications for its practitioners and for society.

Cloning and Biomedical Science

Human procreation is not the only context for evaluating the prospect of human cloning. As a product of biotechnology, a potential means of assisted reproduction, and a possible source of cloned embryos for research and medical use, human cloning also points us to questions about the aims, ends, and means of biomedical science and technology. Ordinarily, we are not prompted to much reflection about what science is for and what goals technology should serve. Our society tacitly accepts the self-directing and self-augmenting character of these activities, and the vast majority of us support them because we esteem and benefit from their contributions to human understanding and human welfare. However, when developments such as cloning raise profound questions affecting fundamental moral values and social institutions, we are forced to consider the ends and means of science and technology, and to explore their standing in the scheme of human goods.

To provide a context for assessing human cloning and its possible benefits, we do well to remember the goals of medicine and modern science: the great value and importance of treating disease and relieving suffering, including the sorrows of infertility; and the great value and importance of gaining knowledge about the workings of nature, our own nature emphatically included. No one can doubt the merit of these noble aims. Yet there has always been some disagreement about the lengths to which we should allow ourselves to go in serving them. Questions therefore arise about the need for limits on scientific pursuits and technological activities, and, conversely, about the meaning of such limits for the scientific and technological enterprises.

To address these questions, we must appreciate the human good of biomedical science in its fullness, and we must ask about the necessary and sufficient conditions for its flourishing. We must recognize, among other things, the unpredictability of scientific discovery and technological innovation, and the importance, therefore, of keeping open lines of inquiry and experimentation regardless of current estimates of their likelihood of success. Although serendipity often favors the prepared mind, nature guards her secrets well, and even the best scientists are regularly surprised by where the keys to the locks are ultimately found.

But precisely because so much of biomedical science is exploratory and experimental, scientific inquiry is not just thought but also action, action often involving research on living subjects, including human beings. And precisely because the use of technologies often has unintended or undesirable side effects, affecting many human goods in addition to health, safety, and the relief of suffering, large questions are necessarily raised when the goods promoted by technology come into conflict with others. For example, is the need to discover new cures for the sick a moral imperative that should trump all other goods and values? If not, then on what basis can it be limited? What moral boundaries should scientists and technologists respect as they continue their quests for knowledge and cures, whether or not they receive public funding? How can society establish and enforce such boundaries? And, on the other hand, how can science and technology be protected against unreasonable limitations imposed by excessively fearful legislators or overzealous regulators?

To be sure, these large questions are hard to answer in the abstract. As a result, they do not recommend themselves for much deliberation. Yet they are very close to the surface of the current debate about human cloning. Moreover, implicit answers to these questions, seldom articulated and rarely defended save by mere assertion, at least color and may even determine what people think should be done about human cloning. A clearer and more thoughtful awareness of the aims of biomedical science could help us assess whether and how human cloning might serve the ends of science and medicine and could help us more fully consider its possible benefits and potential drawbacks.

But we must consider not only the ends of science, but also the means it employs. Cloning, after all, is a technique, a means of reaching some desired end. Even if the purposes it might serve are worthy, it must still be evaluated as a means. Not every means employed in the pursuit of worthy ends can pass ethical muster. This truth is widely recognized in the establishment of canons of ethics regarding the use of human subjects in research. It is also recognized in the established practice of technology assessment, which seeks to find the least problematic and least dangerous means for achieving a desirable end.

For instance, as a means of treating infertility or of providing a suitable source of compatible organs for transplantation, cloning raises difficulties having to do with human dignity and the costs of "manufacture" of the sort discussed earlier. Human cloning also raises questions about the ethics of research with human subjects, with risks of harm to the child-to-be, the egg donor, and the woman who would bring the cloned child to birth, questions that we shall take up in some detail in Chapter Five. Yet the most highly controverted moral argument about human cloning research involves a human subject not always considered when the ethics of research is discussed: the early human embryo. Because all cloning begins with the production of embryonic clones, and because such clones are potentially highly useful in biomedical research, questions of the ethics of means are absolutely central to the debate about the morality of cloning.

Ethical questions regarding the use of human embryos in research are, of course, not unique to cloning. They have been central to the recent and continuing controversy about federal funding of research on human embryonic stem cells, because human embryos produced by IVF offer possibilities for medical advances, beyond their use in assisted reproduction. The use of embryos has aided research on early human development. These embryos are also the source of human embryonic stem cells, pluripotent cellsvii that may be induced to develop into all the tissues of the body. These stem cells thus may hold great promise for future treatment of chronic degenerative diseases and disabilities.

The difficulty arises because the embryos put to use in these ways are themselves destroyed. This fact raises serious and troubling questions about the proper way to regard these nascent human organisms and the morally appropriate way to treat them. Cloning techniques might provide an even more useful source of embryos for biomedical research than current IVF techniques. Human cloning could yield numerous identical embryos, could provide for the study of stem cells derived from individuals known to possess genetic diseases, and might eventually yield transplantable tissues for regenerative medicine that would escape immune rejection. Human cloning-for-biomedical-research therefore brings the moral question of means before us with even greater force. It calls on us to think of the good of medical advances and the relief of human suffering while at the same time considering our responsibilities to nascent human life and the possible harms to ourselves and future generations that may result from coming to regard the beginning stages of human life as raw material for use and exploitation.

While there is almost universal opposition to cloning-to-produce-children, the prospect of using cloned embryos in biomedical research has attracted significant support in the general public and among many scientists, patient advocacy groups, and policymakers. It therefore presents more complicated moral and policy challenges, and requires serious reflection on the duty of society to those of its members who are suffering, as well as its responsibility for nascent life. The precise character of both that duty and that responsibility is a subject of long-standing dispute, giving rise to a contentious but very important public debate.

Cloning and Public Policy

Beneath the current debate about human cloning lie major questions about the relation between science and technology and the larger society. Valuing freedom and innovation, our society allows scientists to inquire as they wish, to explore freely, and to develop techniques and technologies based on the knowledge they find, and on the whole we all benefit greatly as a result. We limit what scientists can do only in certain cases, as when their research requires the use of human subjects, in which case we erect rules and procedures to protect the health, safety, and dignity of the weak from possible encroachments by the strong. In more pervasive ways, we also shape what science does through public decisions about financial support and scientific education. With the uses of technology, we are sometimes more intrusive, establishing regulations to protect public health and safety or to preserve the environment. In rare cases, we even ban certain practices, such as the buying and selling of organs for transplantation. Yet, on the whole, the spirit of laissez-faire governs technological research, development, and use.

But when innovations arise that appear to challenge basic goods that we hold dear, or when the desirability of scientific and technological progress runs up against concerns for the protection of human life and well-being, we are forced to consider the tacit social contract between science and technology and the larger society. The current public and political deliberation about whether and how to restrict or prohibit human cloning forces us to do so in a most powerful way.

In addition, the current deliberation confronts us with the task of balancing important and commonly defended freedoms – the freedom of scientists to inquire, of technologists to invent, of individuals to reproduce, of entrepreneurs to invest and to profit – with the well-being of our society and its members. Circumstances in which otherwise beneficent freedoms can endanger paramount moral and social goods present serious challenges for free societies, and the prospect of cloning presents us with just such a challenge.

This is not an altogether unfamiliar challenge. There are other circumstances in which the freedom to explore, inquire, research, and develop technologies has been constrained. Biomedical science, as we have said, is restricted in its use of human subjects for research, and scientists are required to obtain informed consent and take great care to secure research subjects from harm. Scientific work is also restricted from activities that might harm the health of the general public, and from producing products that may endanger consumers. For example, the federal Food and Drug Administration sits at the juncture between development and marketing of medical products, regulating their introduction and use according to criteria of safety and efficacy. Our society has come to a near-total agreement on the need for such an agency and the importance of its work.

Human cloning, however, does not easily fall into any of the familiar classes of our experience with science. Nor do the ethical challenges it raises fit neatly into the categories of risks to health and safety that are ordinarily the basis of public oversight of science and technology. Raising ethical questions about ends as well as means, cloning is at once a potential human experiment, a possible aid to reproduction, an altogether new sort of procreative technique, a prospective means of human design, and a source of embryos and embryonic stem cells for research. It points back to familiar dilemmas of bioethics – including the ethics of human experimentation and embryo research – and it points forward to the sorts of challenges that will face us as biology gains greater technical prowess. It therefore invites us to think anew about the relationship between society and biomedical science and to evaluate the sufficiency of current institutions and practices that govern that relationship.

The potential dangers we face do not result from ill intent or bad faith. Neither of the prevailing caricatures in the cloning debate – the mad scientist on a blind quest for an inhuman immortality or the puritanical Luddite seeking to keep the future at bay – is accurate, appropriate, helpful, or fair. The challenge we face is not as easy as that. The challenge we face involves the conflict of competing sets of concerns and priorities, each in the service of vital human goods, and each driven by a desire to improve the human condition and to protect essential principles. The widely shared desire to cure disease, relieve suffering, understand human biology, and provide humankind with new and more powerful means of control can conflict, in this case, with the widely shared desire to respect life, individual identity, the dignity of human procreation, and other institutions and principles that keep our society healthy and strong. The challenge for our society is to determine, through public deliberation and thoughtful reflection, how best to adjudicate between these two desires and to determine what form to give to the tacit agreement between society and science, by which society promises freedom within bounds, and science affords us innovation, knowledge, and power while respecting reasonable limits.

The new and distinct challenges that confront us through cloning call upon us to consider the character of that tacit agreement, and to determine whether, and in what way, it might need to be amended and supplemented, especially in the face of the rapidly arriving new biomedical technologies that touch so directly upon our humanity. It is our hope in this report to contribute to just such a thoughtful consideration of the question.

The Report

In Chapter One we present a brief history of human cloning. We summarize the scientific developments, the various public and political debates, and the actions of earlier panels and government bodies.

In Chapter Three we discuss the terminology of the cloning debate. We analyze the controversy over cloning terms, state the terms we intend to use, and lay out the rationale behind our choice of terms.

In Chapter Four we present a survey of the scientific aspects of human and animal cloning. We attempt to clarify what cloning is, where the science stands, and where it may be going.

In Chapter Five we discuss the ethical arguments for and against human cloning-to-produce-children. We consider reasons to create cloned children, concerns over safety and consent, and a series of moral objections.

In Chapter Six we discuss the ethical arguments for and against cloning-for-biomedical-research. We consider the likely medical benefits, the potential social and ethical difficulties, and the concern over the treatment of human embryos.

In Chapter Seven we discuss the public policy alternatives. We consider various options for government action, and present arguments for and against each.

In Chapter Eight, we present the Council's conclusions and offer our recommendations.


  1. The term "human cloning" is used in this chapter to refer to all human cloning: cloning-to-produce-children and cloning-for-biomedical-research. When only one particular use of human cloning is intended, we use the more specific term. A full discussion of our choice of terminology is provided in Chapter Three. Back to Text

  2. Cloning Human Beings, Rockville, MD: National Bioethics Advisory Commission, 1997. Human embryonic stem cells had not yet been isolated at the time of the NBAC report, so the Commission did not offer any recommendations on cloning-for-biomedical-research. Back to Text

  3. Chapter One summarizes selected historical aspects of the emergence of cloning research and public reactions to the prospect of human cloning. Chapter Four summarizes selected aspects of the current state of the relevant science and technology. Back to Text

  4. In order to be sure that we explore fully the human meaning of cloning, we shall examine it in comparison with natural unaided human reproduction, rather than assisted reproduction, say, with in vitro fertilization. The established reproductive technologies do provide some useful points of comparison, but they cannot be taken as the most helpful baseline for understanding the significance of cloning. For that, normal sexual reproduction is the appropriate basis of comparison. Back to Text

  5. The term "sexual reproduction" has two related meanings: the first refers to the act of sexual intercourse that initiates conception by introducing sperm into a woman's generative tract; the second refers to the conception itself, the combination of genetic material from egg and sperm that results in a new organism with a unique genotype. Assisted reproduction techniques like IVF do not involve the former, but do involve the latter and are therefore still rightly considered sexual reproduction. (Likewise, children who are adopted are the fruit of sexual reproduction.) Cloning involves neither, and is therefore described as "asexual reproduction." The second and more fundamental meaning of "sexual reproduction," the union of egg and sperm that results in a new genetically unique organism, is the basis of our discussion in this section. Back to Text

  6. The apparent exception of identical twins is discussed in Chapter Five. Back to Text

  7. Pluripotent cells are those that can give rise to many different types of differentiated cells. See Glossary of Terms. Back to Text

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