A research report that appeared a few days ago suggests that birth control pills are having a profound effect on our programmed biological mechanisms for selecting sex partners and for the evolutionary selection of sex and perhaps other human characteristics.
Little stories tell the tale:
· Before or without the pill it was “Me Tarzan, tough and a good fighter who grabbed you from the other wimpy guys. You Jane, soft and cuddly strange creature, irresistible to me. Let’s go have sex again.” Although Tarzan is a strange animal for her, Jane loves the way he smells and she melts into his arms. Both are responding to biological urges that have kept our species going for millions of years
· With the pill it is more like “Me Alfred, an insurance lawyer. You Bridget, a designer of webs for auto dealers. I found you on Facebook where I liked your little sketches. We are a lot alike. Let’s cook a seafood risotto for dinner together and then we can watch Masterpiece Theatre.” Bridget does not notice anything in particular about how Alfred smells. They don’t have sex very often but that seems quite fine. The biological urge is blunted.
· There is more. Unbeknownst to Bridget, Alfred has been having a torrid affair with Jennifer, a perky Brazilian pizza-delivery girl who is not on the pill. There is something about the way that Alfred smells that drives Jennifer to jump into bed with him. And Alfred cannot resist Jennifer’s allure. At the moment, Jennifer is pregnant with Alfred’s kid and he is working up courage to tell Bridget about that. The biological urge was working again and has done its thing.
The study which appeared October 6 2009 in the journal Trends in Ecology & Evolution is entitled Does the contraceptive pill alter mate choice in humans? Basically, birth control pills disrupt the menstrual cycle. However, the events in the menstrual cycle profoundly affect attractiveness of men for women and women for men and dictate when the sexual urge is mutually maximized. “Female and male mate choice preferences in humans both vary according to the menstrual cycle. Women prefer more masculine, symmetrical and genetically unrelated men during ovulation compared with other phases of their cycle, and recent evidence suggests that men prefer ovulating women to others. Such monthly shifts in mate preference have been suggested to bring evolutionary benefits in terms of reproductive success. New evidence is now emerging that taking the oral contraceptive pill might significantly alter both female and male mate choice by removing the mid-cycle change in preferences(ref).”
The coverage of this study in an October 8 2009 Science Daily article summarizes the situation well. The study shows “emerging evidence suggesting that contraceptive methods which alter a woman’s natural hormonal cycles may have an underappreciated impact on choice of partners for both women and men and, possibly, reproductive success — – Ovulating women exhibit a preference for more masculine male features, are particularly attracted to men showing dominance and male-male competitiveness and prefer partners that are genetically dissimilar to themselves. This is significant because there is evidence suggesting that genetic similarity between couples might be linked with infertility. Further, some studies have suggested that men detect women’s fertility status, preferring ovulating women in situations where they can compare the attractiveness of different women.” – – “Dr. Alverne and colleague Dr. Virpi Lumma reviewed and discussed new research supporting the conclusion that use of the pill by women disrupted their variation in mate preferences across their menstrual cycle.
The authors also speculate that the use of oral contraceptives may influence a woman’s ability to attract a mate by reducing attractiveness to men, thereby disrupting her ability to compete with normally cycling women for access to mate. — Of particular interest is the fact that women taking the pill do not exhibit the ovulation-specific attraction to genetically dissimilar partners(ref).”
Another study reported last year raises similar issues. “The contraceptive pill may disrupt women’s natural ability to choose a partner genetically dissimilar to themselves(ref). ”This study was based on body odors. “Humans choose partners through their body odour and tend to be attracted to those with a dissimilar genetic make-up to themselves, maintaining genetic diversity. Genes in the Major Histocompatibility Complex (MHC), which helps build the proteins involved in the body’s immune response, also play a prominent role in odour through interaction with skin bacteria. In this way these genes also help determine which individuals find us attractive(ref).”
But those body odors are not fully perceived by women who are on the pill. “The research team analyzed how the contraceptive pill affects odour preferences. One hundred women were asked to indicate their preferences on six male body odour samples, drawn from 97 volunteer samples, before and after initiating contraceptive pill use. – “The results showed that the preferences of women who began using the contraceptive pill shifted towards men with genetically similar odours(ref).”
This could be bad news for the stability of a relationship. “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(ref).” (Continuing the little story: When Bridget was finally told about Jennifer being pregnant she stopped having any sex with Alfred and stopped taking the pill. She soon started experiencing Alfred as disgusting and, despite seeing a marriage counselor and the fact that their relationship had been working exceedingly well, she separated from him after two months.)
An interesting question is what the implications of contraceptive pill usage might be for offspring and their evolutionary descendents. Tarzan’s child with Jane and Alfred’s child with Jennifer would seem to continue with the established biological pattern – mating for diversity with male offspring having classical male characteristics and female offspring having classical female ones. Stereotypical! (Jane and Tarzan’s daughter got pregnant the first time when she was in high school.) But what about a child born of Alfred and Bridget or any other couple where the woman is usually on the pill? Would the lack of selection-for-diversity show up as genetic defects? “Disturbing a woman’s instinctive attraction to genetically different men could result in difficulties when trying to conceive, an increased risk of miscarriage and long intervals between pregnancies. Passing on a lack of diverse genes to a child could also weaken their immune system(ref).”
Another interesting question is whether evolutionary selection due to widespread use of the pill will favor people in which traditional male-female odor signaling plays a lesser part in mating and child conception. That could be a partial explanation for why middle-class people in most advanced countries are getting married and having children much later in life. Or, is evolutionary selection happening in which Tarzan is getting to be more Jane-like and Jane more Tarzan-like? Good social arguments can be made that this is happening. As we go now into the third and fourth generations of women on the pill, these questions could become more relevant.
And finally, what about decline and blunting of sexual lust, the great traditional builder of populations? Birth rates are declining in advanced countries where religious norms do not dictate having unlimited numbers of children. Is the pill a major contributor to stabilization of the world’s population not only by cutting down the number of pregnancies but also by blunting natural sexual attractiveness?
As a personal note, I have had 5 natural children by 4 wives and have raised an additional 3 as my own. I fully played ball with the natural biological imperative to reproduce and loved doing so. However, of those eight children I raised, four have not had their own children so far despite the fact that all are over 30.