When men use evolutionary biology to prove that women are passive about sex

 Illustration Credit: "Evolution of Women" by Eduardo Saiz Alonso

Illustration Credit: "Evolution of Women" by Eduardo Saiz Alonso

The Bateman Theory

In 1948, geneticist Angus Bateman conducted an experiment on fruit flies that became foundational to the way biologists understand sexual selection. If you’re familiar with the idea that women are “choosier and less promiscuous” than men when it comes to sex, you have Bateman to thank. His conclusions on fruit flies showed that the female flies more often rejected the males who pursued them than the other way around.

Given that Bateman’s results have been cited over 11,000 times in subsequent research, it might surprise you to learn that his results have never been replicated, and that his experiment had such dramatic design flaws that it “could only have been published if the editor—who should have checked for errors—hadn’t actually read it,” says UCLA evolutionary biologist Patricia Gowaty, whose quotes appear in Inferior: How Science Got Women Wrong by Angela Saini.

The Original Experiment

When Bateman conducted his experiment, his basic setup was to observe 3-5 female and 3-5 male flies and then track their reproductive success. In his observations, ⅕ of males were unsuccessful in producing offspring, compared to only 4% of females. According to Bateman, these female flies had more opportunities to mate than the males, some of whom they continually rejected. Bateman’s findings were forgotten until 1972, when biologist Robert Trivers rediscovered them. He recounts to Saini exactly what that felt like:

“Trivers was just a young researcher at Harvard University, studying mating pigeons outside his window, when one of his tutors suggested he look up Bateman’s work. And he remembers it with graphic clarity. He went to the museum to photocopy it, “with my testicles firmly pressed against the side of the Xerox machine,” he tells me, with a throaty laugh. As soon as he read it, “The scales fell from my eyes,” he says. It would mark a turning point in his career.”

The paper Trivers then published, building on Bateman’s work around sexual selection, marks what Saini calls a “watershed not only in the way scientists understood sexual behavior but also in how the everyday woman and man in the street understood it.” Saini gives the example of Playboy Magazine, which in 1978 had a full-blown feature based on Trivers’s paper, titled, “Do Men Need to Cheat on Their Women? A New Science Says Yes.” Bateman and Trivers were thought to have scientifically validated a common cultural narrative around gender roles and sex: that women receive solicitations from men they frequently reject, thereby controlling when sex happens through their choosiness and restraint.

Those who critically question this dynamic, like yours truly, will be glad to hear that other scientists have poked holes so large in Bateman’s findings that his and Trivers’s papers (and all the sexist theorizing that followed them) are worth disregarding.

Enter Patricia Gowaty

Patricia Gowaty is the scientist behind new studies that not only contradict Bateman’s fruit fly results, but also reveal the mistakes in his design that should invalidate them. In the 1990s, she and her colleagues repeated Bateman’s experiment down to a tee. They got wildly different results. They published their paper in the journal Evolution in 2002, stating, “We observed the movements of females and males in vials during the first five minutes of exposure to one another. Video records revealed females went toward males as frequently as males toward females; we inferred that females were as interested in males as males in females.” Given these new results, Gowaty wondered how Bateman could have arrived at his original conclusions.

When she started looking, she noticed alarming flaws in Bateman’s experiment design. Among several other errors, Bateman had used genetic mutations to distinguish which fruit fly offspring belonged to which parents, even though some of these mutations lowered flies’ survival rates. In other words, his fly subjects could have died before they even had a chance to mate. Add to this the glaring fact that, as Saini summarizes, “Bateman counted mothers as parents less often than fathers, which is a biological impossibility, since it takes two to make a baby.” No wonder Gowaty told Saini that editors must have turned a blind eye in order to let his results see the light of day.

Normally, Gowaty’s findings would have represented a seismic shift in the field. But, alas, men like Trivers -- whose careers now depend on the accuracy of Bateman’s conclusions on sexual selection -- have refused to read Gowaty’s 2012 paper describing these errors. When Saini tried to interview Trivers about the Gowaty’s results for Inferior, she got this response:

“I was afraid you were going to ask that,” he tells me over the phone from Jamaica. “I have not read the God Jesus paper.” He agrees to look at it for me, but doesn’t get around to reading it thoroughly even after a few weeks.”

It’s not only Trivers who refuses to read, (though he eventually admits to Saini that he views Gowaty as a “careful scientist” whose findings are “probably correct”). There’s also Don Symons, the anthropologist whose landmark book The Evolution of Human Sexuality relies on Bateman’s conclusions. He sends Saini a similar note back:

“When I e-mail Don Symons...to ask his opinion on Gowaty’s failure to replicate Bateman’s findings, he tells me he hasn’t read her paper.”

Considering these men are leaders in their field, Saini considers it immeasurably odd for them to ignore papers as significant as Gowaty’s. Make of that what you will.

Further evidence that contradicts Bateman

Perhaps skepticism would have made more sense had Gowaty’s findings been anomalous. But there’s more evidence from primatology and anthropology that also contradict the Bateman/Trivers narrative. For example, some primate species like Hanuman langurs benefit when females mate with as many males as possible, and these females have a social imperative to do so. Similar evidence has surfaced on the promiscuity of female yellow-pine chipmunks and prairie dogs.

Most compelling, in my view, are the actual humans who live in partible paternity communities in South America. In these Amazonian societies, women are encouraged to reproduce with many men, who together co-father her offspring and increase the children’s chances of survival.

So, the next time a man tries to convince you that you’re evolutionarily preprogrammed to want less sex with fewer men, feel free to point them to Gowaty’s first paper here and second paper here. For more detail, you can also send them these anthropological studies on partible paternity groups.


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