What launches guys on serial sexual conquests and prompts solo activity among women?
It's testosterone, of course.
As the primary male sex hormone, it plays a leading role in the sexual development of guys. But folks often overlook the role it plays in female sexuality. Yes, women have testosterone, too, though much less of it -- and it exerts a far different pull, new research suggests.
"It was quite surprising that the link with masturbation was stronger among women than men," said study leader Wendy Macdowall of the London School of Hygiene and Tropical Medicine, in the United Kingdom. "And that among women we saw no link with aspects of partnered sex."
Aside from one, that is. In women, testosterone levels were sharply higher in those who had ever experienced a same-sex relationship.
For the surprising new study, Macdowall's team used mass spectrometry to analyze testosterone levels in saliva samples from nearly 4,000 adults aged 18 to 74. Participants also completed a questionnaire to suss out links between hormone levels and sexual behavior.
Men who had relatively high testosterone (high T) levels were more likely to have had more than one sex partner at the same time during the previous five years, the study found. And straight guys were more likely to have had a recent encounter.
The landscape was different for women.
Those with high testosterone were more likely to have had a same-sex relationship at some point. They also masturbated more often -- and more recently.
High T was also linked to more solo sex for guys. But the masturbation connection was notably stronger among women, the study found.
Participants who had at least one sexual partner in the previous year were asked about problems with sexual function, such as lack of interest or trouble getting or keeping an erection. No link of any kind was found.
As to the link between high T and a greater drive for masturbation among women than men, Macdowall suggested it might ultimately owe to social, rather than biological factors.
Women, she said might be more vulnerable than men to societal pressures and norms -- and those pressures are likely less when they are alone than with another person.
"It's said that masturbation may be a 'truer' measure of sexual desire, because it's a private sexual activity and less governed by social influences," Macdowall explained.
Still, two experts who reviewed the findings said that the overall impact of hormones on the sex habits of both men and women seem to be relatively minimal.
"Ultimately, the bulk of evidence does not support relationships between T levels in the normal range and sex drive or partner number in either sex," said Carole Hooven, a lecturer in human evolutionary biology at Harvard University. "So this is surprising to me."
David Puts, an associate professor of anthropology at Pennsylvania State University, was less surprised at the notion that high T might affect sexual behavior. But, he added, the effect appears to be modest.
"What is especially interesting is why, from an evolutionary standpoint, we see relatively modest relationships in humans compared to, let's say, deer or hamsters," Puts said.
He noted, for instance, that unlike many other animals, people (and our ape cousins) don't have a designated breeding period triggered by hormone surges.
Evolutionarily speaking, Puts added, that could be because our ancestors "probably lived in an environment in which temperatures and food availability were stable throughout the year, and so there was little benefit to restricting breeding to specific times."
So, Puts said, the real question might be: Why do sex hormones such as testosterone still have any impact at all on human sexual behavior? Are some of these hormone-behavior links mere evolutionary holdovers?
Absent an immediate answer, however, Puts said the takeaway is that these effects exist but are not large. "And that variation in sexual interest and activity in each sex is perhaps better explained by other variables, such as social factors," he added.
The findings were published online Oct. 11 in The Journal of Sex Research.
Harvard Medical School has more about the role of testosterone.
SOURCES: Wendy Macdowall, BSc, MSc, assistant professor, public health, environments and society, London School of Hygiene & Tropical Medicine, U.K.; David Puts, PhD, associate professor, anthropology, Pennsylvania State University, Center for Brain, Behavior and Cognition and Center for Human Evolution and Diversity, University Park, Penn.; Carole Hooven, PhD, co-director, undergraduate studies, and lecturer, department of human evolutionary biology, Harvard University, Cambridge, Mass.; The Journal of Sex Research, Oct. 11, 2021, online