Implications of Cloning

by Ben Best

The February 27, 1997 issue of NATURE [NATURE 385:810-813] contains a ground-breaking paper announcing the first successful cloning of a mammal from an adult cell. Dr. Ian Wilmut of Edinburgh, Scotland forced isolated adult sheep cells into a quiescent state by days of nutrient deprivation. Without nutrient, many genes become inactive and the cells revert to the dormant G0 or G1 stages of the cell cycle. The quiescent cells were fused with enucleated oocytes (egg cells). The resulting "zygotes" were allowed to grow into embryos and then transplanted into a surrogate-mother sheep. Literally speaking, these "zygotes" are not full clones when the recipient oocyte is not from the same individual because the mitochondrial DNA is that of another sheep. (For an elementary explanation of the technology of cloning, see The Cloning of Dolly.) By the end of the year 2000, eight mammalian species had been cloned, including mice, cows, sheep, goat, pigs and rats.

World reaction to this breakthrough was mostly a din of anti-scientific hysteria raised by the spectre of possible human cloning. Jeremy Rifkin declared human cloning to be a crime which should be punished "on a par with rape, child abuse and murder." A horde of religious spokespersons warned that humans have "neither the right nor the knowledge to play God". The same cry had been uttered in 1965 after the announcement of the first heart transplant. This argument can be (and often has been) made against every scientific advance. But the argument "if God had meant us to fly he would have given us wings" can easily be augmented with "or a brain to build airplanes". There is certainly no biblical scripture which forbids airplanes, heart transplants or cloning. An October 2002 US opinion poll found that 25% of males approved of cloning humans, but only 10% of females approved [SCIENCE 299:41 (2003)].

Although 277 adult cells were fused with ova, only 13 pregnancies and one live birth resulted. The primary donor cell culture came from the mammary gland of a 6-year-old pregnant sheep. The tissue was 90% epithelial cells, with the rest consisting of fibroblasts, myoepithelial cells and perhaps some relatively undifferentiated stem cells. The cell type (phenotype) of the successful donor cell is unknown. (The fact that the donor cell came from a breast inspired a wag to name the offspring "Dolly" in honor of a well-endowed celebrity of the same name.)

This project was backed by PPL Therapeutics P.L.C., which creates transgenic sheep&cows that produce milk containing human protein that can be used to feed human babies. Rather than go through the tedious&expensive process of creating each transgenic animal individually, the company seeks to produce a flock of cloned transgenic sheep which can then be breeded normally, while still producing the human milk protein. PPL is also working on cloning genetically engineered pigs for animal-to-human organ transplants.

Personally, I have long thought that it would be an excellent idea to improve the quality of the human race — and I have not believed that eugenics necessarily leads to genocide. Nonetheless, I didnt like the idea of entrusting government to conduct a eugenics program. Currently, I think the idea of eugenics is obsolete because science is so quickly approaching the capacity of improving the genetic makeup of individuals. Ironically, many of the anti-eugenicists argue that cloning should be banned because it might undermine genetic "diversity". But banning cloning for this reason is simply another form ofeugenics! In light of the changes I foresee in the next 30 years, I think eugenics or cloning cant have more than a negligible effect upon the quality or quantity of world population.

Some people favor genetic manipulation only for the purpose of ensuring the birth of children free of genetic disease — not for eugenics. For example, a couple with an autosomal (non-sex chromosome) recessive genetic disease that has a 1-in-4 chance of producing a genetically defective child could be given the option of cloning an existing healthy child. Similarly, a nucleus could be transplanted from an oocyte containing mitochondrial DNA that would otherwise result in blindness. The fear of eugenics — even on a voluntary basis — has little basis in fact. The sperm bank of Nobel Prize-winning scientists (the Repository for Germinal Choice in Escondido, California) has resulted in less than 250 children in the 20 years since it was established.

Clones have been caracaturized as being human photocopies — zombies produced for use as slaves. But clones would really be more like time-delayed twins. Currently, one birth in 67 is twins, and the twins invariably have distinct personal identities. A "time-delayed" twin would be even more distinct. There would be no more grounds for treating a clone as a slave that for denying any other person the full charter of human rights. If those who oppose cloning on the grounds that "every human being has the right to be an individual" are to apply this principle consistently, then they would have to demand that one of every twin be forcefully aborted.

Some people fear that evil dictators might clone thousands of copies of themselves. Although this is possible, it seems unlikely to be in the interest of the dictator. A dictators clone would be more likely to overthrow him/her than anyone else. The dictator would have more incentive to clone thousands of his/her most docile subjects. But it would take a generation to do this and other technological change during that period would swamp any possible impact that this could have on global politics.

As a form of ego indulgence, cloning could be costly. If hundreds of clones were made of a beautiful film-star, her beauty would become more available to more men. But the laws of supply&demand dictate that the original would become less precious. So a prudent person concerned about undermining the value of her or his personal uniqueness might hesitate to produce too many clones. To protect against involuntary cloning of a person from a few cells left on a glass or handshake, the DNA Copyright Institute will store DNA information and register that information with the US Copyright Office for a fee of about $1,700. Of course a clone could not be killed, but the creator of the clone could be sued for damages — a deterrent.

Some people have protested that the possibility of cloning represents a threat to "genetic identity". But it might be possible to prevent people from being cloned involuntarily. People could be granted a permanent "copyright" on their DNA. Cloning could require written consent. Conversely, however, the right to ones own DNA implies that one should have the right to make a clone if one so chooses. A woman might be able to give birth to her own clone, but a man would require a surrogate mother (possibly his wife).

Why would anyone want to parent a clone of himself/herself? The intimacy that exists between twins is well-known. The role of genetics in personality is controversial, but persuasive evidence has been discovered that shyness, at least, is a genetically-determined personality attribute (fetuses with fast heartbeats tend to become shy babies). Persons who are genetically unique and experience alienation in the world may find the intimacy&closeness they crave by parenting a clone. The child would be a wanted child, and have a good chance of being raised with loving care. The option of cloning, rather than limiting diversity, will allow for the creation of new kinds of relationships. And it will give people the opportunity to personally explore (& learn-from) the meaning of their own genetic identity.

A childless woman could want to bear the clone of her infertile dying husband. Parents may want to clone a dying & beloved child. Those who condemn such passionate desires as "sick" or "perverted" are no different from other so-called moralists throughout the ages who have sanctified their own bigotry by the claim of divine inspiration. (Commandment Eleven: "Thou shalt not clone".) So-called moralists who accuse defenders of cloning of Nazi eugenics ignore the fact that it is the moralists themselves who are the fascists — invoking the power of the state to impose values on others and measuring human worth by the "naturalness" of conception.

Claims have been made that clones would be parented out of narcissism or for power. But why do people beget children now? Although love was a factor, Im certain that desire for power and enjoyment of power played an important role in my father wanting to have and rear children. And he regarded his children as his property. Similarly, I believe that my mothers desire to be loved and for social inclusion were important factors in her becoming a mother. I dont think that the motives to parent clones would be radically different than those that currently motivate people to have children. Based on the intense closeness that so often develops between twins, chances seem good that very loving parent-child relationships could be created in which there is high level of understanding&empathy of the parent for the child. I dont believe that love is evil — even self-love or love of a clone.

The objection that cloning would provide an option which favors the rich ignores the fact that wealth favors many options — better health-care, better education, vacations, fancy computer equipment and the possibility of larger families. In practice, the families of the wealthy do not seem particularly large now, and large families living on welfare are quite common in industrialized countries with generous "social programs".

A few lesbians have declared that men are now unnecessary. Single people of both sexes may feel that a new option for single-parenting is opening-up. Couples who would prefer to give birth to the clone of a lovable (but childless) aunt or uncle may now be able to do so. The unforeseen social consequences of cloning are not grounds for justifying a ban — and are more likely just another "trampling of rights" by creating a new "victimless crime". If fear of the unknown is allowed to dictate policy, the most predictable result is ignorance.

Arizona financer John Sperling, in an effort to have a clone of his beloved dog Missy, has contributed millions of dollars to the so-called Missyplicity Project at Texas A & M — through a new company called Genetic Savings and Clone. The group was successful in cloning a cat (dubbed "Copy Cat") in February 2002. Cats are evidently much easier to clone than dogs, and the project continues its efforts to clone Missy.

Since 1975 the San Diego Zoos Center for Reproduction of Endangered Species (CRES) has been banking fibroblast cells of endangered species in liquid nitrogen. The cells had been frozen simply to preserve genetic material for future scientific scrutiny. If clones could be produced from fibroblasts, the collection takes on new meaning. Unendangered species could be used as surrogate mothers for the endangered/extinct species cloned from the fibroblasts.

Taking this idea a step further, clones of transgenic animals might be bred which could act as surrogate mothers for human babies. If that were true, then human reproduction would essentially take-on the character of manufacture. It is this prospect which is the most horrifying to those who claim that cloning devalues human life. Clearly, however, a normal person should have no less rights by virtue of having had an animal rather than a human as a surrogate mother. But what if the cloned human was altered to have the brain of a dog? Or the brain of a lobster? Transgenic pigs would probably be a better source of human organs for transplant, but debrained human clones could be of great benefit for pharmaceutical companies wanting humanoid models for testing of experimental drugs.

Transgenic animal clones could be of service in more ways than supplying human milk proteins. Wilmut has suggested that transgenic sheep clones containing the human gene for cystic fibrosis could be used by scientists to learn a great deal about that disease. Immunocompatible neuronal or pancreatic tissue from transgenic animal clones could be transplanted to humans to cure Parkinsons disease and diabetes. Calves have now been cloned carrying human genes for immunoglobulin, making them potential "drug factories" for producing antibodies. Unlike vaccines, which can take weeks to stimulate immunity, the use of such immunoglobulins could confer immediate immunity — of potential benefit against bioweapons as well as in conventional medicine. Knowledge gained by cloning research on the mechanisms of cell differentiation & de-differentiation are very likely to yield insights into means to treat & prevent cancer — and into means to treat & prevent .

Cloning could also have a big impact on animal food production. Biotech start-up company ProLinia Inc. has plans to make extensive genetic changes to farm animals, adding genes to promote disease resistance and make meat less fatty. The US Food and Drug Administration (FDA) has issued warnings to biotech companies Infigen Inc. and Advanced Cell Technology that cloned animals are regarded as "experimental" — that meat & milk of cloned animals are not FDA approved for use as foods.

Although some stem cells are found in adults, the capacity of such cells is restricted, e.g., hematopoietic stem cells only make blood cells. Stem cells from early blastocyst embryos, however, can develop into any cell type ("pluipotent"). When these pluripotent stem cells were first isolated & cultured from human embryos in November 1998, scientists predicted a new era of "regenerative medicine". The current scientific challenge is to be able to (1) learn to direct blastocyst stem cells to differentiate into a specific desired cell type and (2) learn to clone blastocyst embryonic stem cells from somatic cells. "Right-to-life" advocates who believe that embryos have "souls" and those opposed to human cloning oppose both kinds of research.

Cloning is only one of a "family" of new reproductive technologies. The first "test tube baby" (In-Vitro Fertilization, IVF) was born in 1978 when eggs were removed from the ovary of a British woman whose Fallopian tubes were blocked. The egg was mixed with the fathers sperm and placed back in the mothers uterus after the fertilized egg had divided into 64 cells. Babies born by the use of IVF increased in the United States from about 6,000 to about 30,000 per annum in the decade of the 1990s. Typically, IVF embryos are incubated 3 days before being placed into the patients uterus, but 35% of births from this method are twins (the norm is 3% twins), because more than one embryo is placed in the uterus to ensure pregnancy. By incubating for 5 days rather than 3 some clinics are able to carefully select the highest-quality embryo and increase the pregnacy rate from one embyro from 61% to 76%.

Technologies now exist for "purifying" sperm so that the sex of the child can be pre-selected. Haploidization would use as skin cell from one parent to fertilize the egg or sperm of the other parent — a technology similar to cloning insofar as it uses nuclear transfer technology.

Most human stem cells used in research come from the inner cell mass of blastocysts at about day 5 of gestation. Most of these blastocysts are obtained from In-Vitro Fertilization clinics. Women who go to IVF clinics are given hormone injections which cause their bodies to generate 5-15 eggs during a monthly reproductive cycle instead of the usual one egg. The eggs are surgically removed and mixed with the partners sperm in lab dish — with the result that about 3/4 of the eggs result in viable embryos. Several multi-celled embryos are implanted in the womans uterus with the hope that one will survive — and the rest are often cryopreserved in liquid nitrogen for possible future use.

US IVF clinics currently store 100,000-200,000 embryos. If the couple divorces and cannot agree on the fate of the embryos, the embryos remain in "limbo". As women age, it becomes increasingly unlikely they will become pregnant again. Most of the excess embryos will never be used. Some are donated to infertile couples. Most of the embryos donated for research are used by the IVF clinics themselves to improve the in-vitro fertilization process. Use for stem cell research involves costly shipment. It takes up to 10 embryos to make a stem-cell line (cell lines are tissue cultures of cells that can reproduce themselves in a laboratory indefinitely). The embryo cells usually do not survive the process of thawing, transfer to culture and treatment with proteins that break-up the individual cells.

Therapeutic cloning is the process by which a human female donates an egg, a skin cell from a prospective patient is injected into the egg in such a way as to produce a clone and then the embryo is allowed to grow until it contains about 100 cells. The stem cells are then extracted from the embryo and used to differentiate into heart cells, pancreatic cells, neurons, etc. — all of which could be transplanted to the patient without fear of immunological rejection. Stem cells are a potential cure for many degenerative diseases, including diabetes, Parkinsons Disease, Multiple Sclerosis and Alzheimers Disease.

Cloning technology has already been used by Advanced Cell Technology (ACT) to reverse cellular aging, to reproduce an endangered species and to produce transplantable tissues. In the latter process, somatic cells are dedifferentiated to germ cells, and then redifferentiated to stem cells and then to target tissues. This use of cloning technology could produce tissues and even organs for transplant into a donor who provided somatic starting cells (with little chance of immunological incompatibility). ACT was thrust into media limelight by its 25-Nov-2001 announcement of having replaced transplanted a nucleus into a human egg and having coaxed the egg into dividing into six cells — which died before becoming a viable source of stem cells. Significantly, ACT failed in all attempts to transfer the nucleus from adult skin cells — only succeeding in transferring a nucleus from ovary support cells. Opponents of therapeutic cloning are concerned that improvements in these technologies will eventually make human reproductive cloning technology more feasible.

Researchers at the Xiangya Medical College in China claim to have cloned human embryos two years earlier than ACT, but this claim was not verified by publication in a peer-reviewed journal recognized by Western scientists. Biotechnology has strong government backing in China, and few in that nation equate embryo cells with a human being. When a United States delegation to the United Nations argued for bans on all laboratory cloning, they met with firm opposition from China. Singapore has been attempting to establish itself as the stem-cell-research capital of the world through massive funding for biotechnology education & research and a law that permits cloned embryos to be kept for up to 14 days. Alan Colman, head of the team that cloned Dolly in Scotland was lured to move to Singapore.

In February 2004 South Korean researchers succeeded in creating human embryos by placing adult cell nuclei into human eggs to create embryonic stem cells. A 2004 attempt to ban cloning globally was strongly supported at the United Nations by the United States, but failed because of opposition from South Korea, Japan, Australia, India, Belgium and the United Kingdom. Proponents are drafting new proposals.

Regulations concerning embryo research in Israel are also very liberal — and Israel has a large number of IVF clinics. Of the first 12 publications on human embryonic stem cells, 10 included Israeli authors. Researchers at the Israel Institute of Technology (Technion) have created heart cells and insulin-producing cells from human embryonic stem cells, a process that could be lifesaving for heart attack patients and diabetic patients. But the Israelis had no control over differentiation, they simply let the cells grow and picked-out the ones they wanted. Work at Hebrew University in Jerusalem led to the discovery of the role played by growth factors in prompting human embryonic stem cells to differentiate into different cell types.

The US House of Representatives passed a bill which would criminalize therapeutic cloning, but still allow stem cells to be obtained from IVF clinics. US President Bush supported use of federal funds only for research on human embryonic stem cell (hESC) lines existing before the beginning of his speech on the subject on 9-Aug-2001. He estimated the number of such cell lines to be "more than 60", but 20 months later only 11 hESC lines were available for distribution — which does not provide enough genetic diversity to discover novel pathways of differentiation. Moreover, all the pre-Aug-2001 hESC had been created using mouse embryonic fibroblast feeder cells to support them. Human feeder cells have since been developed, which would not have the possibility of contamination with mouse viruses and proteins or the severe restrictions imposed on xenotransplantaion products imposed by the FDA. The moral superiority of using embryos destroyed prior to Aug-2001 is questionable, and the technical inferiority of the resulting hESC lines is unquestionable.

British law forbids cryopreserved embryos from IVF clinics to be stored for more than 5 years, even though the Catholic Church strongly condemns destruction of cryopreserved embryos. British Parliament has allowed therapeutic cloning and creation of human embryos from sperm & egg for research purposes — though the embryos are not permitted to last more than 14 days. But the Parliament later enacted legislation that mandates a prison sentence of up to ten years for anyone cloning a human — the same sentence the American legislation would apply to any scientist attempting therapeutic cloning.

Prior to 1869 the Catholic Church followed Aristotle in the belief that an embryo does not become sufficiently human to acquire a soul until day 40. In 1869 Pope Pius IX excommunicated all who procured abortions — implying that a fertilized egg has a soul. In 1974 (Declarato de Abortu Procurato) the Catholic Church identified a person with a genome — a remarkable bit of materialism considering that individuality is not even established until day 14, beyond which the formation of twins can no longer occur.

If respect for life is the decisive criterion, then the lives of all the sperm that perished without fertilizing the egg must be respected. The Catholic Church should specify at what point of the fertilization process a zygote acquires a soul (When the sperm penetrates the egg? When the male pronucleus is formed? When the DNA of each pronucleus aligns?) and the means by which they make a certain determination. Respect for life should not overlook all of the human patients whose lives could be saved and suffering alleviated by therapeutic cloning.

If a zygote is regarded to have a soul because it is a "potential human being", so should a sperm or egg because they are potentially human. On the other hand, if the sperm or egg cannot be regarded as potentially human until united, how can a zygote be regarded as having an individual soul when twins can occur up to 14 days after the zygote is formed? If science can make a zygote from a skin cell, then the skin cell is potentially human also, and must be regarded as having a soul.

Those who advocate developing potentially life-saving technologies associated with cloned embryonic stem cells are accused of "playing God", but those who would prevent these technologies are "playing God". There is no scriptural authority for forbidding stem cell research and there is no evidence that God means to prevent the use of life-saving technologies. Those who claim to speak for God should take care that they are not arrogantly asserting their own prejudices — for which they may later learn humility.

Religious opponents of cloning often regard the fertilization of a human egg by a sperm and the resulting developing embryo as a holy process not to be tampered with by Humankind through artificial means. Creating a human by In-Vitro Fertilization (IVF) may be only slightly more artificial than creating a human by cloning. Although many religious people oppose IVF & cloning, few have declared that a human created by IVF or cloning would have no soul, be evil or be unloved by God. The Catholic Church morally condemns In-Vitro Fertilization, cryopreservation of embryos and the destruction of embryos — but does not oppose the medical use of embryo tissue which has been obtained from spontaneous abortion (see SCIENCE 293:211, 13-July-2001).

Many Catholics favor stem-cell research — as do a significant number of abortion opponents (many of whom believe that obtaining stem cells from IVF clinic embryos would reduce the temptation to obtain stem cells from aborted fetuses). But pressure from Catholic constituents was enough to cause the American Heart Association to rescind a decision to provide funding for embryonic stem cell research. Many scientists regard the use of stem cells from abortions as no different from the use of cadavers by medical schools.

The controversy over stem cells has prevented much federally-funded research into potential applications. Most of the US patents for embryonic stem cell technologies are held by one company: Geron Corporation. Geron cultivates stem cell lines, but cannot distribute them to many institutions which fear their federal grants could be jeopardized. Limiting federal researchers to the use of existing cell lines could prevent the development of many new cell lines which could potentially be of use — and would enhance the commercial interests of companies which have developed existing cell lines. And it is likely that harmful genetic mutations will accumulate in existing cell lines rendering them useless. Newer and better cell lines would be desirable because most of the existing cell lines have been cultured with animal cells or serum that could be a risk to human health. (Cross-species cloning is also problematic because mitochondria in the egg receiving the cell to be cloned are not sustained by the nucleus.)

Some people who would not otherwise oppose therapeutic cloning fear that such technology could too easily be diverted into cloning humans. Others who favor therapeutic cloning believe that it should only be permitted with fearsome legal consequences for any who attempt human cloning. And others believe that therapeutic cloning is such a "slippery slope" leading inevitably to a pandoras box of biotechnology "nightmares" — such as human cloning, children engineered to custom specifications and brainless humans being grown for spare body parts — that it is better to ban all forms of cloning and to live with the missed opportunity of curing a myriad of diseases than to risk the "nightmares"

The strongest argument against immediate attempts to perfect human cloning is the fact that the process is far from perfected. After all, the 277 adult cells used to create Dolly resulted in one live birth and 12 stillbirths. The production of so many deformed human fetuses and babies would not be tolerated. Adult cells of one phenotype could easily harbour mutations of unexpressed genes, which would become expressed upon the de-differentiation and re-differentiation of cloning. Moreover, the cells in Dolly are 6 years older than they would be.

Even if it were possible to detect defects very early, a firestorm of protest would ensue from anti-abortionists who believe that humanity begins at the moment of conception. Possibly for this reason, and probably also for weaker reasons, the member governments of the World Health Organization has unanimously passed a resolution declaring human cloning to be "ethically unacceptable and contrary to human integrity and morality". US President Bushs bioethics advisor, Dr. Leon Kass, has asserted that cloning "robs us of our humanity" and "risks coarsening our moral sensibilities". In addition to his opposition to cloning, Kass is an anti-life-extensionist who has written, "I think we make a huge mistake if we try to push the life expectancy out to 150 years or longer". (It cannot be an accident that most professional ethicists have obnoxious moral standards — what drives a person to professionally meddle in other peoples lives?).

Even if major countries do outlaw human cloning, there was never much doubt that offshore/underground human cloning research would continue. A UFO cult known as the Realian Movement organized a company in 1997 to clone humans for those who are willing to pay, a service called CLONAID®. Raelians believe that aliens from a UFO contracted the French journalist Rael informing him that they had created humans from DNA 25,000 years ago. The sect has a UFO theme park near Montreal, Canada and is known for uninhibited sexual practices. Numerous members are willing to allow their bodies to be used for surrogate motherhood & cloning — which they believe is the key to immortality.

In March 2001 the Italian Dr. Severino Antinori and the American Professor Panayiotis Zavos announced that they would begin work on creation of a human clone in a secret laboratory at an undisclosed Mediterranean country. Implantation was scheduled to begin in October of the same year. Dr. Antinori has already achieved fame in helping a 62-year-old woman to give birth. Dr. Zavos said that unlimited funds were available for the project from private donors. .

Aside from those who oppose cloning in principal, there are many scientists who believe that much more work should be done with animals before experimenting with humans because of the risk of stillbirths, miscarriages and deformed/abnormal children. Only 10% of cells created by nuclear transfer develop into balls of cells called blastocysts. Of blastocysts implanted in the womb, only one-fifth of the pregnancies are carried to term. And, once born, half the seemingly normal cloned cows & sheep drop dead within three weeks due to fatal flaws in heart muscle or kidney. The surrogate mothers of these clones might also be at risk, because the clones are often abnormally large — with increased frequency of miscarriage [SCIENCE 291:2061-2062 & 2552 (2001)]. Somatic cells do not have the DNA repair capabilities of meiosis, which can make them less reliable as progenitors. In normal development early genes (genes that control the early stages of cell differentiation) are inactivated by cytosine methylation — resulting in high methylation of the adult genome. Cloning should fully demethylate the adult cell, but this process is often faulty. There is currently no test for methylation abnormalities [SCIENCE 292:31 (2001)]. Even when cloning is done using nuclear transfer from embryonic stem cells, the animals that survive have subtle abnormalities in gene expression and, hence, subtle physiological abnormalities [SCIENCE 293:95-97 (2001)].

If cloning technology is not perfected on animals before it is attempted on humans, the prospect of many stillbirths, abortions and genetically diseased human babies raises serious humanitarian concerns. And these humanitarian concerns will provide fuel for the technophobic anti-cloning activists who may be in a position to block the many avenues of research associated with cloning that have such great potential to combat disease & aging.

Although human cloning would be valuable in the long run as a source of new information, in the immediate future it is more of a danger to scientific advancement than a benefit. This does not justify authoritarian efforts to prohibit researchers from cloning human cells — out of fear of increasing the potential for cloning humans. All biomedical research increases the potential for cloning humans — but more important is the potential for saving & extending human lives.

For summaries of legislation in different countries concerning cloning and other controversial biotechnologies see http://strategis.ic.gc.ca/SSG/bb00003e.html .

For a peer-reviewed journal, see Cloning and Stem Cells.

For the latest news about cloning, go to the Yahoo Science Full Coverage Cloning website.


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