Here are a few things that psychologists believe they have learned in the last decade about hormones: During the most-fertile phase of their ovulatory cycles, women become more adept at distinguishing gay men from straight; are more disgusted by unfamiliar foods; are attracted to deeper voices and more-symmetrical faces; prefer potential mates with “creative intelligence,” as opposed to wealth; and are less likely to call their fathers.
Men’s brains, meanwhile, experience their own hormonal baths. In the presence of attractive women, heterosexual men’s testosterone tends to spike, which in turn leads to greater risk-taking. In the days after the births of their children, both men and women have surges in prolactin and oxytocin, which are believed to help build parent-child bonds. And when a man is dominated by others in a conversation or confrontation, his testosterone levels tend to drop.
Those recent findings about hormones and cognition might make decent dinner-party talk. But do these phenomena actually cash out as consequential real-world behavior? Or are they just background blips in the much larger range of psychological and social forces that shape human decision making? A fertile woman might gaze a little longer at a symmetrically-faced man at a bar than she would have a week earlier or later in her cycle. But if she finds herself five years later in a loveless marriage with that same admirably symmetrical man, the explanation probably goes deeper than a single hormonal surge.
“No one factor, biological or social, is going to explain why men and women differ from each other,” says Martie G. Haselton, an associate professor of psychology at the University of California at Los Angeles who is among the most active scholars in the field of hormones and social cognition. “But hormones seem to explain some specific phenomena for which there really aren’t any good competing explanations.”
Haselton and her colleagues hope their work will reveal how humans’ perceptions and decisions are shaped, and sometimes warped, by hormonal effects. But skeptics worry that ovulatory-cycle studies—and especially the way some of them have been reported in the popular press—might bolster sexist stereotypes and crude evolutionary models of human nature. They also say that too much is sometimes being made of small data sets and single studies whose findings haven’t been replicated.
One of the most-discussed recent papers in this genre was published late last year in Psychological Science. In that study, which Haselton conducted with Debra Lieberman of the University of Miami and Elizabeth G. Pillsworth of California State University at Fullerton, 51 female students at UCLA gave the researchers their most recent cellphone bills, identifying each person they had called with a set of initials. They also told the researchers the date when their most recent period had begun. (To be eligible to participate, the students had to be “naturally cycling"—that is, not on the Pill.)
The finding: The students were significantly less likely to call their fathers, but not their mothers, on the days when they were most fertile. And when their fathers called them, those conversations were significantly shorter on fertile days than on nonfertile days, suggesting that the students may have cut them short.
All of this, Haselton and her colleagues speculate, might be evidence that humans have an innate system of inbreeding avoidance. Female animals in several other species are known to avoid their close male kin during periods of fertility, presumably in order to reduce the risk of “biologically costly” sex that would be unlikely to result in healthy offspring. Could these cellphone records offer a distant echo of that animal behavior?
Maybe so. But it is a single study based on a single month’s worth of phone calls. And there is also the question of exactly how to interpret the main finding.
“In some cases with research like this, I’m not sure exactly what would count as falsifying evidence,” says Marlene Zuk, a professor of biology at the University of California at Riverside and author of Sexual Selections: What We Can and Can’t Learn About Sex From Animals (University of California Press). “If they had found the opposite, if they had found that women called their fathers more often during fertility, would that also have been seen as evidence for inbreeding avoidance? Maybe women talk on the phone as a substitute for in-person contact.”
Haselton concedes that the cellphone finding needs to be replicated before it becomes part of the scientific canon. But she says that she always strives to develop clear, parsimonious, testable theories.
She points in particular to a study that examined women’s heightened preferences for stereotypically masculine faces, voices, and personalities during fertility. That basic pattern has been established by multiple studies over a 20-year period. But Haselton wanted to look at how the pattern might affect women’s relationships with their mates, so she and a colleague asked 43 female subjects to complete questionnaires during high-fertility and low-fertility phases across a four-week period. They found that women who viewed their partners as sexually attractive reported feeling more attracted to them during fertility, but that women who rated their partners lower in sexual attractiveness (even if they generally loved and cherished them) spent more time on fertile days noticing and fantasizing about other men.
“That,” Haselton says, “is not a pattern that could really be explained through other hypotheses. It’s something happening below the level of conscious awareness, and it seems unlikely that women would have picked it up through watching TV. It’s not a media-exposure phenomenon. That suggests to me that it’s something deeper, that it’s something tied to reproductive biology.”
Biology, of course, can be a fighting word among social psychologists. Ask Diana S. Fleischman, a postdoctoral researcher at the University of North Carolina at Chapel Hill. “When I was an undergraduate,” Fleischman says, “I mentioned evolutionary psychology in a social-psychology class, and the professor said, ‘Those people are idiots. They say that men prefer to see women in high heels because they think it will be easier to knock them over and impregnate them.’”
Fleischman later embraced evolutionary models when she encountered a more sympathetic psychology professor in graduate school at the London School of Economics and Political Science. “When I was a kid I was always thinking about animal behavior, so this approach seemed natural to me.” In contrast to other psychology paradigms, this one came easily to Fleischman, “because it made sense from the ground up.” (In case her undergraduate teacher believes she is an apologist for male sexual violence, let us note that Fleischman’s current projects include a study of how hormones affect pain sensitivity in women who are survivors of abuse.)
Last year Fleischman and Daniel M.T. Fessler of UCLA published a study of how hormones mediate women’s tendency to avoid threats, both social and medical. During the menstrual cycle’s luteal phase, which comes just after ovulation, women’s immune systems temporarily weaken—presumably to reduce the risk of an immune response against a newly fertilized egg. In their study, Fleischman and Fessler found that women whose progesterone levels spiked the most during the luteal phase were also most likely during that phase to report heightened disgust at unfamiliar foods, increased hand-washing, and increased self-grooming behavior such as pulling at hair or removing dry skin.
Fleischman says it makes perfect sense that women would be hard-wired to increase those behaviors during the luteal phase because their bodies actually are more vulnerable to infection on those days. And this is not mere trivia, she says: If progesterone fuels self-grooming behaviors, then it might be implicated in obsessive-compulsive disorder. If subsequent studies find similar patterns, she says, then new therapies for OCD might emerge—perhaps drugs that reduce the level of progesterone in the bloodstream.
Should we, in some sense, wish for lower levels of all of these hormones in our bloodstreams? Testosterone, for example, seems to play a role in thousands of fatal car crashes each year, not to mention street fights and even wars.
“But if testosterone helps lead us to succeed in risk-taking ventures, then we should be glad of that,” says Saul L. Miller, an assistant professor of psychology at the University of Kentucky who has studied testosterone’s role in a range of social contexts.
In any case, hormones are so deeply embedded in our natures that it makes no sense to imagine ourselves without them. “I don’t think that the conclusion one should draw is that our hormones make us do foolish things,” Haselton says. “Our hormones are probably usually leading us to do things that we wouldn’t think of as irrational, given our normal human biases.”
