Not so long ago, the standard “wisdom” was that human sexual behavior is completely divorced from biology. Hormones like testosterone and estrogen, we were told, influence “animal” mating behavior, but not ours. Female chimps and female dogs go into estrus, but human females did not. A new generation of research findings have challenged that story. The new findings also challenge a related bit of wisdom—that human estrus is hidden—observable neither to women, nor to the men who happen to come within their olfactory sphere of influence.
A host of studies in recent years have demonstrated that women behave differently when they are ovulating— dressing in more provocative ways, boosting their desire to head out to parties, staring more at handsome symmetrical men, and feeling a boost in attraction toward strangers (if those strangers are handsomer than their current partners). A new series of studies by Saul Miller and Jon Maner systematically explores the other side of the equation—how men respond to cues of ovulation in women. One of their more interesting findings is that the presence of an ovulating woman can boost a man’s economic risk-taking.
In the first study, the researchers exposed men to the scent of t-shirts that had been worn by normally cycling women who were not using birth control. They then asked the men to complete word-stems specially chosen to measure the availability of sexual concepts (s _ x; _ _ck; _ ips; _ i _ k; _ ak _ d; _ um; _ l _ t; _ ouch; p _ n _ s; o _ al). Compared to men who had smelled t-shirts worn by non-ovulating women, those fellows who had first sniffed t-shirts worn by ovulating women were more likely to complete “s _ x” as “sex” instead of “six” or “sax,” “_ ak _ d” as “naked” as opposed to “baked” “faked” or “raked,” and “_ _ck” as (expletive deleted, but you get the idea).
The second study involved a sort of projective test. Men were asked to smell t-shirts, and were told they were worn by women who had been asked to relive an emotional event while she wore the t-shirt. To what extent was she feeling angry, fearful, happy, or sexually aroused? In reality, the women had simply slept in the t-shirts while they were ovulating or not. The researchers also administered a test of the men’s sensitivity to smells (with items such as ““I am easily alerted by odorous/pungent substances”). Men who scored high on sensitivity to odors guessed that the ovulating women were more sexually aroused.
In a third study, men actually interacted with a female student who was in cahoots with the experimenters. The woman had been keeping track of where she was in her ovulatory cycle, and been instructed not to wear any perfumes, not to eat any odor-laden foods, not to wear make-up, and to dress in the same non-provocative way for every session (wearing a plain t-shirt and a pair of jeans, with her hair pulled back in a pony-tail). She had also been trained to act in a consistent and non-flirtatious way with each male subject. The men were led to believe she was simply another subject who had signed up to be in the same experiment at the same time as they did. One of the experimental tasks involved spending 5 minutes building a structure out of Lego blocks. While working on the task, the female put her left elbow on the desk, placed her left hand so that it covered her chin and cheek, and proceeded to slowly piece together Legos with her right hand. Using a hidden camera, the experimenters recorded whether the man mimicked her nonverbal behaviors (previous research has shown that we are more likely to adopt the postures of people when we want them to like us). After that, the man was asked to play a game of Blackjack on a computer with the female sitting behind and watching his choices.
Men were more likely to mimic the woman’s nonverbal posturing on the days when she was ovulating, suggesting they were more interested in her. And most interestingly, the woman’s ovulatory cycle influenced the men’s economic decisions—the guys made riskier decisions on days when the woman was ovulating.
Ovulation and Deep Rationality
Earlier, I discussed another set of findings indicating that ovulation also altered women’s economic decisions—with ovulation inspiring more to spend more money on sexy clothing (see When women are in heat, the economy warms up). Findings such as these are in line with what my colleagues and I call Deep Rationality—the view that economic decisions, although irrational on the surface, often reflect an underlying evolutionary logic.
If you consider the fact that humans are mammals, and that we have all the same hormonal and pheromonal systems that other mammals have, the new findings may be unsurprising. The more interesting question might be: Why did scientific experts ever believe that human sexual behavior operated outside the biological world? I think part of the answer is that we overestimate the role that conscious decision-making plays in our social behaviors. We are very bright, and we do use our consciousness to obsess over our relationships with other people. That misleads us into believing that we understand our underlying motivations. Instead, it may be that, for important decisions such as those involving, biological motivational systems do much of the goal-setting behind the scenes, and we tap into consciousness only to figure out how to best meet those goals (a man knows he is attracted to chocolate and to beautiful women, but he doesn’t need to know why, and he doesn’t need to know what triggers the ups and downs in those attractions, he merely needs to figure out how to get to the nearest Godiva outlet, and to come up with something clever to say on the gift card so his lover will share a truffle with him after she’s physically shown her appreciation for the thoughtful gift).
Durante, K.M., Griskevicius, V., Hill, S.E., Perilloux, C., Li, N. P. (2010). Ovulation, female competition, and product choice: Hormonal influences on consumer behavior. Journal of Consumer Research, Released Online: DOI: 10.1086/656575.
Kenrick, D.T., Griskevicius, V., Sundie, J.M., Li, N.P., Li, Y.J. & Neuberg, S.L. (2009). Deep rationality: The evolutionary economics of decision-making. Social cognition, 27, 764-785. (special issue on the rationality debate).
Miller, S.L., & Maner, J.K. (2011). Ovulation as a male mating prime: Subtle signs of women’s fertility influence men’s mating cognition and behavior. Journal of Personality & Social Psychology, 100, 295-308. doi: 10.1037/a0020930
Miller, S. L., & Maner, J. K. (2010). Scent of a Woman: Male Testosterone Responses to Female Olfactory Ovulation Cues. Psychological Science, 21, 276–283. doi:10.1177/0956797609357733