Pre-natal Parent-Offspring Conflict: Human pathologies explained by Ev. theory

Pregnancy can be the most wonderful experience life has to offer. But it can also be dangerous. Around the world, an estimated 529,000 women a year die during pregnancy or childbirth. Ten million suffer injuries, infection or disability.Dr. David Haig argues that a mother and her unborn child engage in an unconscious struggle over the nutrients she will provide it. Dr. Haig's theory has been gaining support in recent years, as scientists examine the various ways pregnancy can go wrong.In the 1970's, Dr. Trivers argued that families create an evolutionary conflict. Natural selection should favor parents who can successfully raise the most offspring. For that strategy to work, they can't put too many resources into any one child. But the child's chances for reproductive success will increase as its care and feeding increase. Theoretically, Dr. Trivers argued, natural selection could favor genes that help children get more resources from their parents than the parents want to give.As Dr. Haig considered the case of pregnancy, it seemed like the perfect arena for this sort of conflict. A child develops in intimate contact with its mother. Its development in the womb is crucial to its long-term health. So it was plausible that nature would favor genes that allowed fetuses to draw more resources from their mothers (than their mothers should be selected to give ABE - EZ).A fetus does not sit passively in its mother's womb and wait to be fed. Its placenta aggressively sprouts blood vessels that invade its mother's tissues to extract nutrients.“We tend to think of genes as parts of a machine working together," Dr. Haig said. "But in the realm of genetic conflict, the cooperation breaks down." In a 1993 paper, Dr. Haig first predicted that many complications of pregnancy would turn out to be produced by this conflict.Dr. Haig also made some predictions about the sorts of maternal defenses that have evolved. One of the most intriguing strategies he proposed was for mothers to shut down some of the genes in their own children . . in the past 15 years, scientists have identified more than 70 pairs of genes in which the copy from one parent never makes a protein. Scientists do not fully understand this process, known as genomic imprinting.One of the most striking examples is a gene called insulin growth factor 2 (Igf2). Produced only in fetal cells, it stimulates rapid growth. Normally, only the father's copy is active. To understand the gene's function, scientists disabled the father's copy in the placenta of fetal mice. The mice were born weighing 40 percent below average. Perhaps the mother's copy of Igf2 is silent because turning it off helps slow the growth of a fetus.
Dr. Haig's work is now widely hailed for making sense of imprinted genes. "Molecular biologists had it worked out in exquisite detail, but they had no idea why it existed," said Kyle Summers, a biologist at East Carolina State University. "Haig just comes in and says, 'I know why this is happening,' and explained it."Dr. Haig has recently been exploring his theory's implications for life after birth. "I think it can influence all sorts of social behaviors," he said.Scientists have found that some genes are imprinted in the brain after birth, and in some cases even in adulthood. "Imprinted genes and behavior are the new frontier," said Dr. Lawrence Wilkinson of the University of Cambridge. In a paper to be published in The Philosophical Transactions of the Royal Society of London, Dr. Wilkinson and his colleagues argue that the evidence on imprinted brain genes ” preliminary as it is ” fits with Dr. Haig's theory. They call it "the most robust evolutionary hypothesis for genomic imprinting."Dr. Haig has enjoyed watching his theory mature and inspire other scientists. But he has also had to cope with a fair amount of hate mail. It comes from across the political spectrum, from abortion opponents to feminists who accuse him of trying to force patriarchy into biology."People seem to think, 'He must have a political agenda,' " Dr. Haig said. "But I'm not talking at all about conscious behaviors. I'm just interested in these mechanisms and why they evolved."