Unlucky in love: "T-shirt sniffing" studies have shown that the birth control pill causes women to select partners who are genetically similar to themselves.
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Increased chance of divorce
"Our study shows for the first time that the pill [actually] shifts preferences towards genetically similar men," said Roberts. He speculates that this may not only increase the chance of separation or divorce if the female partner stops taking the pill, but could also reduce a couple's chances of conception.
"If pill use increases the chance of selecting a more genetically-similar partner than a woman would otherwise choose, then, when the woman comes off the pill to start a family, she may find it harder to conceive." Children of genetically similar parents are more likely to have birth defects that cause them to be naturally aborted in the womb.
Alexei Maklakov, an evolutionary biologist from the University of New South Wales in Sydney, Australia, thought the study was interesting, but said that it's difficult to extrapolate findings like this to the population at large, because the study subjects used are not a random sample of the population.
"Unfortunately, it is impossible to use true randomised trials when analysing human reproductive behaviour," said Maklakov. "For this reason, it is always difficult to get around the fact that subjects are not a random sample from the population."
The study group was not representative of the population at large because a financial incentive was offered to encourage women to participate and because the researchers had no control of who would start taking the pill during the study.
MHC genes are an important part of the immune system, and experts think variety within the complex is important to offer the best protection against disease.
The theory is that new combinations of genes slow the rate at which disease pathogens can evolve to break through our defences, and this is why we have evolved to favour partners with different MHC genes to our own.
