Ulterior Motives

How goals, both seen and unseen, drive behavior

Good Sex Is Good for Relationships

Oxytocin and the intimacy boost.

My evolutionary psychology colleagues have a fascination with what they affectionately call "human mating." Obviously, sex and sexuality is an important part of human experience, and it is important to have a theoretical framework for trying to understand sex differences in sexual strategies. Plus, if the headlines splashed on supermarket magazine covers are to be believed, we all like to read about sex, so it makes for good reading.

Unfortunately, many evolutionary approaches take a fairly narrow view of sexuality, by starting with the role of sex in reproduction. This discussion needs to be broadened.

To caricature the evolutionary psychology approach to human mating, these views assume that animals with internal conception (like humans) require a larger parental investment by the female than by the male. Thus, males should be prone to mate with many females to try to maximize the probability of conception. Because conception is internal, there is paternity uncertainty, so females should try to get the best genes possible for their future offspring, but should also try to gain resources from males to support the unborn children.

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Unfortunately, a lot of human behavior gets missed by this approach. Lots of people stay married for a long time. Couples that are the happiest tend to be those with the best sex lives. People continue to have sex long after they are able to conceive children.

An interesting study in the November, 2008 issue of Psychological Science by Christian Unkelbach, Adam Guastella, and Joseph Forgas helps shine a light on an aspect of sexuality that is under-appreciated in many discussions of sex that come out of evolutionary psychology.

They did a study on a group of men who were given either a dose of oxytocin or a placebo. Oxytocin is a chemical that is released in men and women during orgasm. It plays other roles as well, but we'll focus on that one for now.

The men in this study were then given a recognition test for positive and negative words related to sex, relationships, other positive emotions, and words unrelated to positive emotion at all. This recognition test was set up to determine the degree of accessibility of the words. As frequent readers of this blog will remember, concepts that are more accessible tend to have a stronger influence on behavior than concepts that are less accessible.

This study observed that oxytocin made positive words related to sex and relationships more accessible relative to the placebo condition. Other words (including words for positive emotions) were not influenced. This finding suggests that oxytocin release will make it easier for men to act in a positive and loving way toward their sexual partners. This study was done only with men, but similar kinds of results have been obtained with women as well.

So, it is important to recognize that sex plays an important role in strengthening relationships in a way that goes above and beyond mere procreation. To be clear, I am not saying that the principles that evolutionary psychologists use are all wrong, only that the discussion needs to be broadened.

Art Markman, Ph.D., is a cognitive scientist at the University of Texas whose research spans a range of topics in the way people think.

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