Women who take oral contraceptives are attracted to a different type of romantic partner than they would be if they did not take the pill, new British research suggests.
Researchers at the University of Liverpool and the University of Newcastle found that women who take the birth control pill were more likely to be attracted to a partner who was genetically similar to themselves.
Traditionally, humans are attracted to partners who are genetically dissimilar as a means of maintaining genetic diversity.
The researchers asked 100 study subjects to indicate which of six male body odour samples they preferred both before and after starting to use the birth control pill.
Humans are attracted to the body odour of prospective partners. Genes in the Major Histocompatibility Complex (MHC) help develop a person's distinct body odour by how they interact with skin bacteria.
The researchers found that women's body odour preferences changed after they began taking the pill to favour men with similar odours to their own.
Genetically similar partners have more trouble conceiving, a higher risk of miscarriage and extended time periods between pregnancies.
As well, a child who inherits a less diverse mix of genes has a higher risk of developing a weakened immune system.
As well, "not only could MHC-similarity in couples lead to fertility problems but it could ultimately lead to the breakdown of relationships when women stop using the contraceptive pill, as odour perception plays a significant role in maintaining attraction to partners," Craig Roberts, a lecturer in evolutionary psychology at the University of Liverpool and a lead study author, said in a statement.
The researchers could not say for sure how the pill may affect a woman's choice of partner. However, they did speculate that there could have been pre-existing behavioural differences between the study subjects who took the pill and those who did not, particularly among those who were in relationships and those who were not.
The findings are published in the journal Proceedings of the Royal Society B: Biological Sciences.
Abstract:
MHC-correlated odour preferences in humans and the use of oral contraceptives
S. Craig Roberts, L. Morris Gosling, Vaughan Carter & Marion Petrie
Previous studies in animals and humans show that genes in the major histocompatibility complex (MHC) influence individual odours and that females often prefer odour of MHC-dissimilar males, perhaps to increase offspring heterozygosity or reduce inbreeding. Women using oral hormonal contraceptives have been reported to have the opposite preference, raising the possibility that oral contraceptives alter female preference towards MHC-similarity, with possible fertility costs. Here we test directly whether contraceptive pill use alters odour preferences using a longitudinal design in which women were tested before and after initiating pill use; a control group of non-users were tested with a comparable interval between test sessions. In contrast to some previous studies, there was no significant difference in ratings between odours of MHC-dissimilar and similar men amongst women during the follicular cycle phase. However, single women preferred odours of MHC-similar men while women in relationships preferred odours of MHC-dissimilar men, a result consistent with studies in other species suggesting that paired females may seek to improve offspring quality through extra-pair partnerships. Across tests, we found a significant preference shift towards MHC-similarity associated with pill use, which was not evident in the control group. If odour plays a role in human mate choice, our results suggest that contraceptive pill use could disrupt disassortative mate preferences.
