A new paper in the scholarly journal Trends in Ecology and Evolution suggests that oral contraceptives may influence women’s choice of mates, with potentially enormous effects on their quality of life and their ultimate reproductive success.

Commonly used hormonal birth control methods such as Yasmin, Seasonale, Ortho Tri Cyclen, Nuvaring and Loestrin, while extremely effective at preventing unwanted pregnancy, may well have previously unsuspected effects on a woman’s choices of both long-term and short-term partners. This is of interest to the more than 100 million women around the globe who use oral contraceptives, and their sexual partners, too.

The paper, published October 9th, was authored by biologists Dr. Alexandra Alvergne and Dr. Virpi Lummaa at the University of Sheffield in England. It analyzed a large body of research that had gone before. Writes Dr. Alvergne, lead author of the study, “The use of the pill by women, by changing her mate preferences, might induce women to mate with otherwise less-preferred partners, which might have important consequences for mate choice and reproductive outcomes.”

Researchers have long known that women make different sexual choices during their most fertile phase than they do during the rest of the month. This is called cycling mate preferences, and quite simply, it means that most women choose more masculine and symmetrical faces when they are ovulating or close to ovulation. They are also uncharacteristically attracted to dominant males, and most likely to engage in infidelity at this time in their cycle. During the rest of their cycle periods when the women are more likely to be infertile they are more attracted to less masculine faces, and men who are better choices as long-term partners.

Oral contraceptives work by mimicking pregnancy and stifling ovulation, which flattens out the hormonal cycles usually experienced by a fertile woman. Why is this a concern? Says the paper:

New evidence suggests that the pill, by eliminating oestrus, changes the natural cycling preferences in women for markers of both genetic quality and compatibility in mates as well as natural cycling attractiveness to men. As compared with normally cycling women, pill users show no or weaker preferences for facial and vocal masculinity. For instance, the preferred face shape is more masculine during the high conception-probability phase of the menstrual cycle in non-pill users, but pill users do not show similar preference.

The possibility is that a woman could make a choice influenced by birth control that is perhaps not in her best reproductive interests. Even worse, with our cultural customs of lifelong mating and marriage, a woman could change her contraceptive practices and find that she is not attracted to her mate in the same fashion as she was when she was under the influence of prescribed hormones. Either of these outcomes could be devastating to a paired couple.

Oral contraceptives are still regarded as one of most effective forms of birth control available to women (they trail the intra-uterine device by a fraction of a percentage point, but the IUD is appropriate for fewer patients, and is rarely prescribed for women who have not already gone through childbirth). Birth control pills are affordable, simple to obtain, and work extremely well. However, this paper has given us all something to think about: the possibility that altering the hormonal cycles of the human female en masse could have significant reproductive effects for individual women, and the entire species, too.

More research is forthcoming in this arena, and the results are sure to be fascinating.