'Males Are Naturally More Promiscuous Than Choosy Females'
The junk science story from the 1940s that just won't go away
One of the "everyone knows" statements that I come across most often is the one saying that men are just naturally more promiscuous than women. They are supposedly biologically designed to spread their seed with an evolutionarily sound mating strategy and this explains human mating behaviors — for all humans.
Besides the fact that beliefs that come from "everyone knows" are nearly always mostly or totally wrong, these particular ones about men being naturally more promiscuous as an evolutionary mating strategy come out of a highly problematic scientific experiment done in 1948 — on fruit flies. Nonetheless, the Bateman principle, as it came to be known, has almost taken on a life of its own over the years and is still an oft-cited and much referenced bit of research.
The fact that Bateman's research has never had a strict repetition ought to be concerning considering that replicability is one of the hallmarks of scientific validity, but it doesn't seem to matter.
Bateman's experimental study of Drosophila melanogaster produced conclusions that are now part of the bedrock premises of modern sexual selection. Today it is the most cited experimental study in sexual selection, and famous as the first experimental demonstration of sex differences in the relationship between number of mates and relative reproductive success. We repeated the experimental methodology of the original to evaluate its reliability. The results indicate that Bateman's methodology of visible mutations to assign parentage and reproductive success to subject adults is significantly biased. Source
The above study, one of many that has reached the same conclusions, doesn't seem to have made much of a dent in the strong belief in Bateman's findings. This cultural narrative continues nearly three quarters of a century later for the same reason that it was embraced in the first place — because it creates story that is appealing to some people and reinforces patriarchal norms. The fact that Bateman's research has never had a strict repetition ought to be concerning considering that replicability is one of the hallmarks of scientific validity, but it doesn't seem to matter.
When Patricia Adair Gowaty's team took on trying to replicate Bateman's study in 2012 they noted serious flaws in his methodology which resulted in biased results.
Bateman's study was taken as a scientific confirmation of Darwin's theory because it fit a popular, albeit rather Victorian narrative.
"Here was a classic paper that has been read by legions of graduate students, any one of whom is competent enough to see this error," Gowaty said. "Bateman's results were believed so wholeheartedly that the paper characterized what is and isn't worth investigating in the biology of female behavior."
"Our worldviews constrain our imaginations," Gowaty said. "For some people, Bateman's result was so comforting that it wasn't worth challenging. I think people just accepted it." Source
Darwin was probably the first to publicly opine that across species, males were randy and promiscuous and that females were reticent and choosy. Bateman's study was taken as a scientific confirmation of that theory because it fit a popular, albeit rather Victorian narrative. But what evolutionary biologists have discovered in the past several decades is that this isn't necessarily so.
Aside from the fact that many primate females are far from sexually reticent or choosy, across all species, mating with several males confers a significant evolutionary benefit.
Gowaty describes the benefits of multiple mates as an answer to the never-ending evolutionary struggle against what may be the world's greatest predator: disease.
In this illness-driven arms race, organisms that produce offspring from multiple mates are more likely to produce some children with the right antibodies to survive the next generation of viruses, bacteria and parasites. Source
Both male and female Barbary macaques mate repeatedly in rapid succession. Female chimpanzees are often sexually aggressive, and when primatologist Sarah Hrdy first described the ribald antics of female hanuman langurs she had witnessed in her field research to the scientific community of the 1970s, it created a scandal.
More than 30 years of subsequent research has confirmed Hrdy's findings and expanded on them to reveal that females in many primate species, humans included, engage in a diversity of sexual strategies to enhance their overall reproductive success. For example, in saddle-backed tamarins, females will solicit sex from multiple males who will each help to care for her offspring.* Female mouse lemurs will mate with up to seven males during a single night. Capuchin monkeys will seek out mating opportunities in the early stages of their pregnancy, presumably to confuse males about paternity. And bonobo females will have sex with everybody at pretty much any time they feel like it. Source
In addition to primates, in many bird and several insect species females mate with more than one partner. For example, an estimated 90% of bird species are socially monogamous but scientists have begun to discover using genetic and behavioral studies that in some species up to 75% of the offspring may come from "extra-pair copulations." In other words, mama bird had some other sexual partners other than just the one she was tending the nest with.
Cooperative polyandry occurs among The Galapagos hawk, as females will mate with up to seven different males during the mating season. Throughout the nesting period, the female and her multiple male partners take turns incubating the eggs and feeding the offspring. Wattled jacana females display resource defense polyandry, mating with multiple males on her territory and laying clutches of eggs within intervals of less than two weeks. Source
Aside from the fact that Bateman's research methodology was terrible, why on earth would any reasonable person generalize the behavior of fruit flies to humans? Why did generation after generation of scientists overlook the blatant flaws in both his research and his conclusions? Despite all of this, what we know now is that Bateman had it pretty much all wrong.
Females can gain benefits, such as reduced infanticide risk or assurance of fertilization, from mating with multiple males (polyandry). Similarly, the assumption that males will always exhibit indiscriminate mating has also been challenged by comparative studies, particularly in insects, in which the energetic costs of sperm production, courtship and copulation can select for male choosiness and the prudent allocation of mating effort. Source
It always makes good sense to look at the larger picture, to consider multiple angles for any conclusion, and to be skeptical of a research study that cannot be replicated using the same methodology. But unfortunately, too often, even within the scientific world, narratives that seem right because they meet cultural expectations can be embraced as truth.
People who bother to look and pay attention have known for a long time that Bateman's conclusions were wrong, but most people don't want to pay attention beyond "everyone knows" sorts of stories that confirm their existing beliefs and biases. As one group of researchers noted in the conclusion of their look into Bateman's work,
Our field might profitably do some soul-searching: Why were Bateman's obvious errors overlooked for so long? As we said in our primary report, legions of graduate students have for the past 40 years read and discussed Bateman. Why did they not bring attention to the errors? Surely all of them, among biologists at least, understand the elements of mutation, inheritance and Mendelian genetics. Why did their professors not challenge Bateman's results? We are inclined to the idea that Bateman's results and conclusions are so similar to status quo, dominating world-views (competitive males, dependent females) that pre-existing cultural biases of readers may have dampened skepticism and objectivity. Perhaps lack of repetition is simply due to lack of professional incentives such as funding for repetitions. (Although that doesn't explain why so few people ever pointed to the glaring errors in methodology — comment mine) Source
As another group of researchers noted, "We argue that human mating strategies are unlikely to conform to a single universal pattern." Unlike animals, we have to also factor in social norms, which may vary slightly from culture to culture and from era to era. In some places in the world even now, partible paternity, where several men have sex with a woman and are considered the father of her child is a long-standing practice. It spreads fatherly feelings throughout the group which helps to maintain solidarity and cohesion as well as promoting the well-being of a greater number of children. And of course, in a lot of places, strict monogamy (at least institutionally, if not in actual practice) is the norm.
Deciding that patriarchal mores are supported by science (when they aren't) is really just another way for this social system to try to justify itself. But for a long time it's worked. A lot of people still believe this stuff and pass it along as gospel truth because it makes sense to them in a patriarchal context — because that is mostly what they've known — but that doesn't mean that it is actually true. "Everyone knows" is cultural currency but it isn't scientific fact. For me, I'd rather know the truth.
© Copyright Elle Beau 2022
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