February 20, 2013
Men Owe Their Superior Spatial Skills To Blind Luck
Jedidiah Becker for redOrbit.com — Your Universe Online
In recent decades, a plurality of studies have emerged confirming an age-old, cross-cultural gender stereotype with which we´re all familiar — namely, that the average man has (slightly) better spatial-navigational skills than the average woman. As study after study has buttressed what appears to be a case of natural chauvinism, the go-to explanation for the discrepancy has gone something like this: The males who first acquired this improved sense of direction had a so-called “adaptive advantage” which helped them leave behind more offspring than their spatially inept peers, eventually allowing this characteristic to spread throughout the entire male population of Homo sapiens. The rest, as they say, is evolutionary history.Or is it? A new study spearheaded by a University of Illinois researcher challenges this explanation of male spatial superiority, claiming that there is no hard evidence to support it and suggesting a lesser-known alternative explanation in its place. A report of the team´s study appears in the latest edition of The Quarterly Review of Biology.
Justin Rhodes, a University of Illinois psychology professor and eponymous head of the Rhodes Lab, conducted a meta-survey of 35 separate studies that looked at territorial ranges and spatial skills in 11 different animal species. These animals included humans, rhesus macaques, horses, deer mice, lab mice, meadow voles, pine voles, prairie voles, rats, cuttlefish and an obscure little burrowing rodent known as talastuco-tucos native to Argentina.
In eight of these 11 species, Rhodes´ team says that males did in fact have slightly better spatial skills than their female counterparts. This superiority held true regardless of how large or small their respective territories, or how far away they roamed from their home bases.
So far so good, as these findings only reaffirm what researchers have known for years. However, Rhodes points out that these studies also offer subtle support for little-known contending hypothesis about the origins of spatial-navigational superiority in males. According to this alternative theory, the male´s improved ability to keep his bearings is nothing more than a “side effect” of his higher levels of testosterone.
In support of this explanation, Rhodes points to a number of previous studies that have demonstrated that women who are given a regular regimen of testosterone injections experience improved spatial-navigational skills.
THE “CREATION STORY” BIAS
Rhodes believes that his team´s study and others like it help to paint a more complex, nuanced picture of the evolution of a variety of little-understood human characteristics. He also highlights what he believes is a worrisome tendency among many biologists to look for a specific evolutionary advantage in every single human trait. This bias, he believes, has led many researchers to develop fallacious “creation stories” that try to explain unusual human phenomena — such as the female orgasm, menopause or even rape — by inventing an imaginary “advantage” that these odd characteristics must have conferred in mankind´s evolutionary history.
For instance, some evolutionary psychologists have attempted to interpret the origin of rape as an alternative mating strategy for males who were unable to obtain a mate and leave behind offspring through less aggressive means. Other researchers have hypothesized that the purpose of menopause was to allow aging women a reprieve from reproduction in order to give them the time and energy to care for their grandchildren.
While many of these evolutionary narratives seem entirely plausible and may even be true, the problem, says Rhodes, is that they simply aren´t testable in most cases. And while countless studies in the fields of psychology and neuroscience have highlighted the natural human predilection for creating fluid stories in which every event has meaning, the simple fact is that many physical and behavioral traits — in humans as well as other organisms — arise as a matter of chance, as the mere epiphenomena of other random events. And still other characteristics may ride in on the coattails of others, so to speak, as the byproducts of traits that offered real evolutionary advantages.
“For example, women have nipples because it´s an adaptation; it promotes the survival of their offspring,” Rhodes explained. But it would be nonsense to invent an “adaptive” explanation for why males also have nipples, he continues. “Men get it because it doesn´t harm them. So if we see something that´s advantageous for one sex, the other sex will get it because it´s inheriting the same genes — unless it´s bad for that sex.”
And Rhodes suspects that this logic might also hold true for a man's superior spatial skills. Men have higher levels of testosterone than women because this plays an enormous role in the development of a number of critical sexual characteristics. However, it seems that improved spatial skills and a better sense of orientation are likely little more than a fortuitous side effect of higher testosterone levels.
According to Rhodes, scientists who insist that superior spatial skills in men are the direct result of an adaptive advantage bear a burden of proof and must explain why women did not also inherit superior spatial skills from their fathers.
“The only way you will get a sex difference [in an adaptive trait] is where a trait is good for one sex and bad for the other. But how is navigation bad for women? This is a flaw in the logic,” he says.
In the bigger picture, Rhodes believes that evolutionary scientists should work on developing a healthy sense of skepticism toward convenient narratives for explaining every trait of every organism in terms of adaptive advantage.
“When people hear arguments made or stories told, particularly about human behaviors being products of adaptation, I think they should ask the question: ℠Where is the evidence?´"
Rhodes is a member of the Beckman Institute for Advanced Science and Technology at Illinois. Members of his research team also included a professor of philosophy from the University of Wisconsin at Madison and a scientist from the University of California at Riverside.