At one of the oddest press conferences ever, Brigitte Bosselier, a "bishop" in the Raelian UFO cult announced today that the group's cloning company, Clonaid has succeeded in cloning a baby girl named Eve. Citing privacy concerns, Bosselier offered no proof for her extraordinary announcement. However, Clonaid says that it has agreed to let an independent panel chosen by science journalist Michael Guillen determine whether Eve is in fact a clone of her mother. If it's on the up and up, the world should know in little more than a week whether the first human clone has been born or not.

What would a clone be? Well, he or she would be a complete human being who happens to share the same set of genes with another person. Today, we call such people identical twins. To my knowledge no one has argued that twins are immoral. Of course, cloned twins would not be the same age. But it is hard to see why this age difference might present an ethical problem—or give clones a different moral status. We should treat all clones like we would treat identical twins or triplets. It would be unethical to treat a human clone as anything other than a human being.

There are many misconceptions about human cloning. For example, some people apparently believe that cloning can bring back or replace a dead child or other loved one. They have bought into a popular but naïve idea of genetic essentialism—that genes are a recipe for making the same person. However, considering the case of the natural clones called twins helps us think clearly about what clones produced in vitro would be like. Twins are clearly distinct individuals with different points of view because twins have two different bodies and two different brains. Individuality does not reside in our genes, but in our brains and bodies.

Some people oppose human cloning because they worry that clones' lives would be "less open" than people produced in the conventional way. Clones would be born with certain expectations, goes the argument, because people with their exact set of genes would have come before them. The novel genomes produced through sexual reproduction somehow confer more openness to the lives of their carriers.

This is genetic essentialism again. Even twin studies find only a 50 percent to 60 percent correlation in characteristics such as intelligence and temperament. Clones, who will be twins displaced in time, and who will therefore have very different life experiences, will likely share even fewer similarities with their genetic forebears. Anyone seeking to make exact duplicates of themselves or other loved ones through cloning is going to be very surprised.

One moral objection often heard is that cloned children would be not ends in themselves, but would be means for their parents' self-aggrandizement (not to mention the means of aggrandizement for Raelian beliefs). And sadly this may be true for some cloned children, but it also true for many children born today in the conventional way. On the other hand, the considerable emotional and financial investment that the parents of cloned children will be making indicates that these children will be very much wanted and treasured by their families.

Once the public understands more completely the limitations of cloning (for example, that one can't bring back the dead), human cloning will likely be used mostly by infertile couples who have no other choice for bearing biologically related children. For the rest of us, producing children the old-fashioned way will remain a lot more fun and a lot cheaper.

One of the chief problems in cloning mammals so far has been its inefficiency—it takes many failed embryos to produce one healthy cloned animal. Right now, only 2 percent to 4 percent of mammalian clones are long-term survivors. Why such a low survival rate?

Many cloned mammal fetuses, e.g., pigs, calves, and sheep develop severe abnormalities. For example, some clones produce larger than normal placentas, others are born twice as big as normal, and some are born with deadly anatomical flaws, like enlarged hearts or defective kidneys.

Researchers suspect that the abnormalities result from parental genomic imprinting. Genomic imprinting is seen only in placental mammals (like humans) and is a result of the biological battle between the sexes. Males want their offspring to survive and so favor large progeny, females who need to reserve nutritional resources for themselves tend to favor smaller progeny. Thus imprinted paternal genes tend to promote fetal growth (such as fetal growth factor, Igf2) while maternal genes inhibit fetal growth (a gene known as H19). The size of the offspring is determined by the balance of these factors.

To make a long story short, the problem with mammalian cloning may be that the genes from nuclei from mature cells may have lost their proper imprinting due to aging. So when these mature nuclei are inserted into enucleated eggs to produce embryos, their imprinting is wrong. Since there is currently no way to restore it, either paternal or maternal genes affecting fetal growth may end up being dominant, creating the developmental imbalances seen in cloned animals. There is no test now available for checking on whether genes are properly imprinted or not, so bringing a healthy clone to term is largely a matter of chance.

One might counter that attempts at human reproductive cloning are little different from the first efforts at in vitro fertilization in which researchers implanted scores of embryos before the first one worked, bringing Louise Joy Brown, the first "test tube" baby, into the world. However, in the case of in vitro fertilization, animal research had identified no problems with increased birth defects resulting from the procedure. That's clearly not the case with mammalian cloning right now. A good benchmark for deciding to proceed with human reproductive cloning would be when researchers are reasonably sure that clones would suffer no more likelihood of birth defects (about 2 percent) than do children produced by sexual reproduction, either in vitro or by conventional means. It's way too early now.

If Eve is in fact a clone and she is healthy, she and the Raelians are incredibly lucky or they are concealing a lot of lost and defective fetuses.

Should the federal government and other governments outlaw attempts at human reproductive cloning? Reproductive cloning is not intrinsically immoral, but attempting to clone a human being now can be thought of as behaving so negligently that one has a high likelihood of maiming a person. It is appropriate to protect people from extremely negligent behaviors. However, bans unfortunately have a way of becoming permanent. How about a ban limited to five years during which research on the cloning of other mammals proceeds? One of the worst things that could happen to the hopes of infertile people who look to reproductive cloning as a way of having genetically related kids, would be for today's hasty cloning efforts to produce defective children. Public revulsion at such an occurrence could set back reproductive cloning for decades.