by Angela Saini
Similarly, in other small-scale societies where women contribute more to the family plate, women tend to have more sexual freedom. In the United States, notes Scelza, “in sub-populations in which reliability on male resources is low as a result of high incarceration rates and unemployment, female kin provide critical instrumental and emotional support, and patterns of serial monogamy are common.”
Another example is in South America, where some isolated societies practice partible paternity, the belief that more than one man can be the father of a baby. In a paper on the topic in the journal Proceedings of the National Academy of Sciences in 2010, Robert Walker and Mark Flinn at the University of Missouri, Columbia, and Kim Hill at Arizona State University write, “On the universal partible paternity end of the spectrum, nearly all offspring have purported multiple cofathers, extramarital relations are normal, and sexual joking is commonplace.”
Tracking reproductive success in populations across the world, including Finland, Iran, Brazil, and Mali, researchers Gillian Brown and Kevin Laland at the University of St. Andrews and Monique Borgerhoff Mulder at the University of California, Davis, similarly found huge variation. In their paper published in the journal Trends in Ecology and Evolution in 2009 they said the data are “inconsistent with the universal sex roles that Bateman envisaged.”
All this, says Scelza, punctures the biological model of the coy, chaste female. Working with the Himba, who have a sexual culture so different from her own, has taught her that the rules about how women and men behave in relationships have far more to do with society than biology. The Himba aren’t a breed apart. They’re just culturally different. “It’s not that they don’t have love. It’s not that sex has replaced love in this society. They feel jealous. But the cultural norms that are in place prevent men from really being able to act upon it,” she explains. “If he was, for example, to hit his wife or something like that, which in some places in the world is completely an acceptable response, there would be a backlash. He would probably end up having to pay a fine and be punished for that action.”
If there is a difference in sexual behavior, adds Scelza, it’s that Himba women seem to be more discriminating than the men. “I think they’re still being picky. But I think being picky doesn’t mean one partner and you have to stick with them for life.”
Where does this all leave Angus Bateman’s cherished principles?
As more evidence rolls in, researchers have started to further question the scientific orthodoxy that females are generally more passive and chaste than males. Even the famous 1978 experiment on the campus of Florida State University—which found that men were overwhelmingly more open than women to casual sex with strangers—has been repeated, with surprising results.
“I felt like it wasn’t telling the whole story,” explains psychologist Andreas Baranowski from Johannes Gutenberg University. In the summer of 2013, he and colleague Heiko Hecht decided to run Clark and Hatfield’s seminal study again, this time controlling for certain factors they felt might have affected the original outcome. They were driven by their own personal observations of dating and sex. They instinctively didn’t believe that the Florida State University experiment had captured the true spectrum of how women behave. “It wasn’t what my experience was in Germany here, or in Europe in general. And also of other colleagues and friends,” Baranowski tells me. “My female friends would tell me about hookups and stories about how they would engage in sexual relationships with men, and that’s also not represented in the data at all. So it was a bit like, that is weird.”
Baranowski and Hecht suspected that women might reasonably be put off having sex with a stranger for lots of good reasons, including the social stigma of getting picked up so casually and, more obvious, the risk that they might be attacked. “We wanted to find out how the original findings would stand up to a more naturalistic setting, such as a cocktail bar, and a more safe setting, namely a laboratory,” they wrote in their paper, published in the journal Archives of Sexual Behavior in 2015. They wanted to make sure they didn’t veer too far from the original experiment either, so they ran it on a university campus as well.
Both on the campus and in the cocktail bar, they got fairly similar results to Clark and Hatfield, with slightly more men than women agreeing to a date, and many more men agreeing to sex. In both cases, though, men weren’t nearly as keen to go on dates or have sex compared to the Florida State University experiment. It wasn’t proof that Clark and Hatfield had got it wrong, but it was certainly evidence that different places and times can yield different results.
And this was crucial in showing that there’s no one way in which the sexes typically behave. The original experiment just wasn’t representative. “It’s really one dimensional, representing the dating market in the United States on a university campus in the seventies. That’s how I felt about it,” says Baranowski. “I didn’t doubt that they did proper protocol. I think they did. It’s just a microcosm there, where they did the experiment.”
Where their data got really interesting, though, was in the lab. They wanted their subjects to believe they were going on genuine dates with real people, so the researchers concocted an elaborate ruse based on a dating study. Each person was shown ten photographs of strangers of the opposite sex and told that all these strangers wanted to go on a date or meet up for sex with the subject in particular. If they agreed to meet, they were given a safe environment, and Baranowski and Hecht’s research team would then film the first half of their encounter.
All the men in the study agreed to go on a date and also have sex with at least one of the women in the photographs. For women, the figure was 97 percent agreeing to a date and, unlike the first experiment, “almost all women agreed to have sex,” says Baranowski.
It was evidence, they noted in their paper, that gender differences are significantly smaller in a nonthreatening environment. It may not have been biology holding women back in the Florida State University experiment but other reasons, most likely social and cultural—like the fear of violence or a moral double standard. One sex difference they did notice in the laboratory setting, though, was that women tended to pick out fewer partners from the photographs they were offered. Like Brooke Scelza found with the Himba in Namibia, they were choosier than the men, but not less chaste.
“We can’t just go on pretending that everything is hunky-dory.”
“Things like Bateman’s principles actually don’t make sense to me,” says Patricia Gowaty, distinguished professor at the University of California, Los Angeles.
We’re sitting on the patio of her home on a mountain in Topanga, nestled in a sprawling state park in Los Angeles County. We’re surrounded by wildlife. At one point during our meeting, a wild deer wanders nearby. Gowaty is an animal expert, an evolutionary biologist and a firebrand who has spent her career, which spans five decades, to leaching sexism out of her field by challenging its basic assumptions. Her most famous target has been Angus Bateman’s 1948 experiment showing that male fruit flies are more promiscuous than females.
“I became a scientist at the same time as I was becoming a feminist. They were coincident,” she tells me. Gowaty’s feminism has never waned. It influences her now as much as it did when she had her first job in the education department at the Bronx Zoo in New York in 1967. “In the late 1960s, all over the country, there were groups that were coming together to consciousness raise. The idea of consciousness-raising was simply to talk and to bring to consciousness the ideas associated with the feminism that was emerging at that time.” Through forums like these, she began to understand how women throughout history, including her own mother, had been constrained. Their achievements were against the odds.
“There are many women of my generation who have published with their initials to hide their gender,” she tells me.
Gowaty was angered, just as her contemporaries Sarah Hrdy and Adrienne Zihlman were, by how evolutionary biology was ignoring and misunderstanding women. Ba
teman’s principles lay beneath some of the claims that angered her most. She spent thirty years studying the mating behavior of Eastern bluebirds, and in the 1970s, when she suggested that female birds were flying away to mate with males that weren’t their partners, she simply wasn’t believed. Her male colleagues couldn’t accept it. They told her instead that the female bluebirds must have been raped.
“I think one of the things that Bateman’s principles do is they obfuscate variation in females. So suddenly, there’s nothing interesting about females. That’s one of the things that bothers me about it. There’s embedded sexism there, I think,” she says. “They may as well be tenets of the faith.”
Gowaty knew that the ultimate test of any scientific experiment rests on the ability to replicate it. So in the 1990s, after studying Bateman’s paper in detail, she decided it was time to do exactly that. What she and her colleagues at the University of Georgia, Rebecca Steinichen and Wyatt Anderson, found contradicted Bateman in the most fundamental way. “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,” they wrote in their paper, published in the journal Evolution in 2002.
This raised the dilemma of just how Bateman managed to see what he claimed to see in his own fruit flies. Investigating further, Gowaty soon began to notice problems with Bateman’s study. In a subsequent paper, published in 2012 in Proceedings of the National Academy of Sciences, Gowaty and researchers Yong-Kyu Kim and Wyatt Anderson at the University of Georgia, wrote, “Bateman’s method overestimated subjects with zero mates, underestimated subjects with one or more mates, and produced systematically biased estimates of offspring number by sex.” They claim that Bateman counted mothers as parents less often than fathers, which is a biological impossibility, since it takes two to make a baby.
Another error is that the same genetic mutations Bateman needed his flies to have so he could distinguish the parents from their offspring also affected the fruit flies’ survival rates. A fly with two severe and debilitating mutations, such as uncomfortably small eyes and deformed wings, could have died before Bateman had the chance to count it. This would have almost certainly skewed his results, too.
The mistakes are so clear, claims Gowaty, that Bateman’s 1948 paper could only have been published if the editor—who should have checked for errors—hadn’t actually read it. Failure to replicate scientific findings is a big deal. Often it leaves grave doubts about the original experiment. And for an experiment as important as Bateman’s it should cause enormous concern.
In this case, though, the reaction to her findings has been mixed. “A lot of people were very excited about it, other people were pissed about it. . . . It was like they were mad,” she tells me. When I e-mail Don Symons, who wrote The Evolution of Human Sexuality in 1979, to ask his opinion on Gowaty’s failure to replicate Bateman’s findings, he tells me he hasn’t read her paper. When I ask instead for his broader thoughts on the evidence of multiple mating in females, he tells me that he’s no longer available to answer my questions for personal reasons.
I also ask Robert Trivers, who first popularized Bateman’s paper in 1972, for his 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. “Since Patty is a careful scientist my bias is that she is correct,” he finally tells me by e-mail. Even so, he adds that research on other species (including his research on a Jamaican giant lizard) has reinforced Bateman’s principles. He sends me a paper published a couple of months earlier in the journal Science Advances by a team of European and US researchers. It reviews examples from more than a century of animal data, concluding, “Sexual selection research over the last 150 years has not been carried out under false premises but instead is valid and provides a powerful explanation for differences between males and females.”
For Gowaty, this defense isn’t enough. Picking out examples in the animal kingdom that happen to be consistent with Bateman’s principles ignores the wealth of inconsistencies—including, it seems, fruit flies. If there is enough contradictory evidence, this should put the underlying theory in doubt. The principles can’t be considered principles if there are so many exceptions. The problem is that Bateman’s and Trivers’s ideas have taken on such a life of their own that this no longer appears to make much difference. “I think people are hung on Bateman’s principles. They say that the principles stand whether the data are right or not,” says Gowaty.
The failure of prominent scientists such as Symons and Trivers to read her work when it was published makes it even more difficult for Gowaty to make the wider scientific community aware of her findings.
“I find it tremendously strange,” says animal behaviorist Zuleyma Tang-Martínez. “When a paper like that comes out, you would think that people who are interested in the topic would read it, regardless of which side they’re interested in or which side they tend to agree with. I try to read papers by people who don’t agree with my position. And I can’t imagine just saying, ‘Oh, I didn’t bother to read it.’ That to me seems almost insulting to a fellow scientist, to take that attitude.”
For Gowaty, this is more than a professional frustration. “I think that our inability to see alternatives is associated with our commitment to see sex differences. The canon of sex difference research is about sex roles and the origin of sex roles and the fitness differences that supposedly fuel those. These arguments are the ones that we really need to understand in order to make inferences that are reliable. I happen to think that the canon is flawed, and it’s flawed because it starts with sex differences to predict other sex differences. It is essentialist,” she explains.
“Many of these theories that we have in evolutionary biology about sex differences are not fundamental theories. They’re hand-wavy as hell.”
That’s not to say Bateman was completely wrong. Only that he wasn’t entirely right. If we were to judge Angus John Bateman’s principles today, it’s likely that the jury would be out. “I think, certainly, there are species that fit that mold,” says Tang-Martínez. In a review of evidence she published in the Journal of Sex Research in 2016, she lists the red-backed spider, pipefish, and seed beetles as examples of creatures that support Bateman’s hypothesis.
“But I do think that given the amount of evidence all the way across the board, from male investment and cost of sperm and semen, all of the sort of original underpinnings of his whole idea, that we have to rethink,” Tang-Martínez adds. “We can’t just go on pretending that everything is hunky-dory, and that we can still apply Bateman across the board to all species.”
She describes his principles as a box. As time wears on, fewer species—including humans—seem to fit in the box. Indeed, it’s possible to argue that if ever there was proof that females aren’t naturally chaste or coy, it’s the extraordinary lengths to which some males go to keep them faithful.
“Let me tell you one anecdote from birds,” Robert Trivers tells me.
It’s from his graduate student days, when he would watch the pigeons on the gutter outside his third-floor window. In the winter, the birds would huddle together in rows for warmth. “You have two couples sitting next to each other in winter. They may have sex in December, but it’s nonreproductive, trust me. Throughout the winter they’re not having sex together; they’re just staying together, and they intend to breed together in the spring as soon as breeding season arrives,” he begins.
The issue for the males is how to make sure they don’t lose their female partners to another male. Trivers imagines himself as one of the male pigeons. “If you have four individuals sitting next to each other, then the males sit on the inside, even though they are the more aggressive sex,” he explains.
“I sit in between the other male, who sits to my right, and my female sits to my left. He, meanwhile, has his female to his right. So both of us can relax during the night. We’re in between any other male and our female.” This arrangement means that each male can successfully protect his female from unwanted attention from the other male in their huddle.
But a dilemma sets in when another couple is added to the mix. With three males and three females, things get complicated. “Now it’s impossible to have a seating arrangement such that each male is between his female and all the other males,” he says. “So what you get instead is the outer two, the far left male and the far right male, each have their mate on the outside of them. So they’re protecting their mate from contact with the other males.” This leaves one male in a quandary. “Now, what about the central male? What does he do?” he asks me. “What he does is he pecks his female and forces her to sleep on the slanting roof several inches above him and several inches above the seat she would prefer to be on, which is sitting on the gutter, on which she would have a male on both sides of her.” The male forces her to sit alone uncomfortably in the cold.
As a student, Trivers would sometimes work until three in the morning. “So at one thirty, I would hear some ‘woo hoo-hoo,’ and I would see, ha ha! What happened is the male has fallen asleep and the female has crept back down to the comfortable position, which is how she would prefer to sleep the night. He wakes up and sees she is there, and pecks her back up into this uncomfortable position!” he says. “The sexual insecurity or the risk of an extra-pair copulation is strong enough to make me willing to inflict a cost on my mate.”