Volume 11, No. 7—October 2001  
Table of contents for this issue  
 
HYPOTHESES

Single-Egg Theory
Immaculate Conception Without God
By Jim Holt

WHEN DOES A HUMAN LIFE BEGIN? Opponents of abortion and stem-cell research, like the Roman Catholic Church and the right wing of the Republican Party, draw the line at the moment of conception. Could it be that they are drawing it not too early, as those on the other side of the debate maintain, but too late?

At conception, an egg and a sperm come together to form an embryo. The egg and the sperm, everyone seems to agree, are not by themselves human beings. Why? Because, as Robert P. George, a professor of jurisprudence at Princeton University, recently put it in a Wall Street Journal Op-Ed, "they lack the epigenetic primordia for internally directed growth and maturation as a distinct, complete, self-integrating human organism." What Professor George was presumably getting at is the fact that the egg and the sperm each have just half the number of chromosomes needed for human development. They are, to use the technical term, haploid cells. Only when their nuclei fuse do you get a diploid cell—that is, one with a complete genetic blueprint for a person.

But consider another, quite different scenario. Start with an unfertilized egg in a sperm-free environment. Now suppose the nucleus of this egg were to divide and the resulting pair of nuclei were to fuse as if one of them came from a sperm. This cell would then be a diploid cell. What would prevent it from developing into a full-blown organism the same way a fertilized egg does?

In fact, that is precisely what happens in many kinds of animals, including reptiles, amphibians, and birds. The phenomenon is called parthenogenesis, from the Greek for "virgin birth." Parthenogenesis was discovered (in aphids, as it happens) in the eighteenth century by the Swiss naturalist Charles Bonnet. By the twentieth century, biologists had figured out how to induce it artificially; exposing frog eggs to salt water, they found, could start the sequence that led to tadpoles and mature frogs, even in the absence of sperm.

But what about higher animals? Despite occasional claims made by unmarried pregnant teens in "Dear Abby" letters, there are no documented cases of parthenogenesis in humans. A couple of researchers have reportedly got the process under way in rabbits and mice, only to see the parthenogenetic fetus abort spontaneously well before birth. The problem seems to be that most of the instructions that cause the placenta to form in fetal mammals are carried by the chromosomes of the sperm. The egg also has genetic instructions for constructing the placenta, but those bits of its DNA are switched off by a chemical coating. Thus successful parthenogenesis in humans would require stripping off this coating and turning those genes on again.

Is this possible? In 1984, a committee on bioethics set up by the British government and chaired by the Cambridge University philosopher Mary Warnock declared, "We consider that there is no possibility at present of inducing parthenogenesis, or 'virgin birth' as it is commonly known, in humans, and indeed we do not believe such a development will take place in the foreseeable future." Since then, however, manipulation of DNA at the molecular level has become fairly routine in the laboratory, and no major technological obstacles now appear to stand in the way of producing an adult human from an unfertilized egg.

The possibility of parthenogenesis eliminates any ethical distinction between an unfertilized egg and an embryo—at least according to the biologist Harold J. Morowitz and the physicist James S. Trefil in their 1992 book, The Facts of Life (Oxford). "Imagine that you have a fertilized egg, a conventional zygote, in one test tube and an unfertilized egg in the other," they write. "Left to themselves, they would both perish. Each, however, has the potential of becoming a human being, provided that it is supplied with the appropriate machinery. In the case of the zygote, that machinery is the mother's body. In the case of the unfertilized egg, that machinery involves a laboratory and then the mother's body."

To those who argue that the machinery needed by the unfertilized egg to become human is unnatural, Morowitz and Trefil respond that it is "no more unnatural than the incubator used to keep a premature infant alive, and certainly less unnatural than in utero surgery." By this line of reasoning, an unfertilized egg is, like a frozen embryo, a developable (but not a developing) human life. The destruction of a frozen embryo for the purposes of stem-cell research is thus of no greater ethical moment than the destruction of an unfertilized egg at the end of a woman's menstrual cycle.

If parthenogenesis becomes a practical possibility, a curious inversion could take place in reproductive politics. It is not hard to imagine anti-patriarchal forces coming to revere the unfertilized egg even more than conservatives now revere the embryo. Indeed, they might find that virgin birth has a number of advantages over cloning and sexual reproduction, quite apart from the fact that the parthenogenic fetus, untainted by male seed, can scarcely be regarded as a trespasser in the mother's body. For one thing, it generates only females, since the self-fertilized egg is bound to have only two X chromosomes. It's twice as efficient as sex, since two partho-genic virgins can have twice as many babies as one woman and one man. Unlike cloning, parthenogenesis does not produce exact genetic replicas of the parent, since each egg (like each sperm) has a unique genetic makeup. Also unlike cloning, it is available only to women, since the man's yolk-less sperm cells are barren. A lesbian feminist's dream?

JIM HOLT

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