Are Males Genetically Doomed?
By Steven Stocker
The decaying Y chromosome could limit men's futures.
The human Y chromosome is a genetic mess. It's accumulated so many mutations over the years that only a handful of active genes remain. When these decay, all men will be infertile and the human species will become extinct.
So predicts Bryan Sykes, genetics professor at Oxford University, in his book Adam's Curse: A Future Without Men. Sykes proposes two solutions to head off extinction—one that rescues men from the genetic junk pile and one that dispenses with men altogether and perpetuates the species using only women.
According to Sykes, the problem started about 200 to 300 million years ago among mammas' ancestors, when mutations first provided the Y chromosome with genes that direct the embryo to develop into a male.
Damaging mutations may be corrected through recombination, when chromosomes from the mother sidle up to their counterparts from the father and exchange genetic material. but sex chromosomes (the X and Y chromosomes) are largely denied the opportunity to correct.
Y chromosomes are more in need of this genetic healing than are X chromosomes because of the hothouse conditions inside the testes. Cells are dividing rapidly day and night in order to produce hundreds of millions of sperm per day. This involves much copying of DNA in order to produce the chromosomes needed for the sperm. Since mutations occur when DNA is copied, the chromosomes being packaged into sperm contain many mutations. For most of the chromosomes, the mutations can be corrected in subsequent generations if they wind up in the sperm that fertilizes the egg, but not for the Y chromosome. In contrast to the testes, conditions in the female germ cells in the ovary are downright mellow. The germ cells that give rise to the eggs go through only 24 divisions before the eggs are released for fertilization, so fewer opportunities arise for mutations.
So how long does the Y chromosome have left? Taking into account just the rate at which Y chromosomes are decaying and not counting any deleterious environmental effects on fertility, such as those caused by pesticides, Sykes assumes that 1% of men in each generation will be 10% less fertile than their fathers. At this rate, fertility will drop to 1% of its current level within 5,000 generations, or about 125,000 years. This is about the same length of time that it took humans to evolve from their beginnings in Africa, so we are about halfway through our life span as a species.
Sykes assures us that we should not feel that the universe has singled us out for extinction. He suspects that a good many species have already disappeared because of Y chromosome decay. However, he points out that extinction is not necessarily a foregone conclusion. In 1995, researchers discovered a small rodent called the mole vole that does not have a Y chromosome. Apparently, the genes needed to switch on the production of male characteristics have been transferred to some other chromosome. Sykes suggests that perhaps humans should follow the lead of the mole vole and, using genetic engineering technology, cut the male-forming genes out of the wreckage of the Y chromosome and transfer them en masse to some other chromosome. This reconstructed chromosome, then, would be the new male sex chromosome and would operate just like the old one. Men and women could continue reproducing through sexual intercourse.
Another possibility, says Sykes, would be to abandon men entirely and fertilize eggs with other eggs, instead of with sperm. This would occur only in the laboratory. The nucleus of the second egg, which contains chromosomes from one mother, would be injected into the first egg, where it would fuse with the nucleus containing chromosomes from the other mother. The resulting embryo would always be a girl. In April 2004, Japanese researchers reported in Nature that they had produced a female mouse by fusing two mouse eggs. It wasn't easy. Out of 457 egg fusions, 371 embryos developed to the stage that they could be implanted into surrogate mothers. From this, only 10 mouse pups were born, and only one survived into adulthood. Nevertheless, this study showed that sperm could be rendered superfluous.
With tongue only partially implanted in cheek, Sykes suggests that this latter approach may help save humanity from destruction. He states that many of the world's problems—such as wars, poverty, and environmental degradation—are at root caused by runaway sexual selection. Men stop at nothing to accumulate wealth and power so that they can mate with as many women as possible—and the women go along with it. Eliminate the need for men to perpetuate the species and women will be free to rule the world in a more egalitarian and harmonious fashion. All will be sweetness and light.
Or at least that's the theory.