Males' superior spatial ability likely is not an evolutionary adaptation

February 19, 2013

(Phys.org)—Males and females differ in a lot of traits (besides the obvious ones) and some evolutionary psychologists have proposed hypotheses to explain why. Some argue, for example, that males' slight, but significant, superiority in spatial navigation over females – a phenomenon demonstrated repeatedly in many species, including humans – is probably "adaptive," meaning that over the course of evolutionary history the trait gave males an advantage that led them to have more offspring than their peers.

A new analysis published in The Quarterly Review of Biology found no support for this hypothesis. The researchers, led by University of Illinois psychology professor Justin Rhodes, looked at 35 studies that included data about the territorial ranges and spatial abilities of 11 species of animals: cuttlefish, deer mice, horses, humans, laboratory mice, meadow voles, , , rats, rhesus and talastuco-tucos (a type of burrowing rodent). Rhodes and his colleagues found that in eight out of 11 species, demonstrated moderately superior to their female counterparts, regardless of the size of their territories or the extent to which males ranged farther than females of the same species.

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The findings lend support to an often-overlooked hypothesis, Rhodes said. The average superiority of males over females in spatial navigation may just be a "side effect" of testosterone, he said. (Previous studies have shown that women who take testosterone tend to see an improvement in their spatial navigation skills, he said.)

The analysis adds a new dimension to an ongoing debate about the evolutionary significance of some baffling human traits. Rhodes and his colleagues object to "creation stories" that seek to explain sexual phenomena like the female orgasm, rape or menopause by hypothesizing that they evolved because they provided an . Some evolutionary psychologists describe rape, for example, as an alternate mating strategy for males who otherwise are reproductively unsuccessful. Others say menopause evolved in women to enhance the survival of their genes by increasing the time spent nurturing their grandchildren. Some of these hypotheses seem intuitive, Rhodes said. "But these stories generally are not testable."

Researchers tend to overlook the fact that many physical and behavioral traits arise as a consequence of random events, or are simply side effects of other changes that offer real evolutionary advantages, he said.

"For example, women have nipples because it's an adaptation; it promotes the survival of their offspring," Rhodes said. "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."

Similarly, scientists who claim that the different spatial skills in men and women are adaptive must explain why women failed to inherit the superior spatial skills of their navigationally enhanced fathers, Rhodes said.

"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," he said. "But how is navigation bad for women? This is a flaw in the logic."

"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 said.

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9 comments

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frajo
3 / 5 (4) Feb 19, 2013
We cannot compare the spatial navigation abilities of the sexes in hunter-gatherer times. Hence we cannot exclude that contemporary differences are just a (random) side effect of settlements.
PoppaJ
2 / 5 (4) Feb 19, 2013
Ahhhhhhhhh I have a headache!!!
First it states
""Males' superior spatial ability likely is not an evolutionary adaptation""
.........then states..........
""is probably "adaptive," meaning that over the course of evolutionary history the trait gave males an advantage that led them to have more offspring than their peers.""
.........then it states.......
""slight, but significant,""

This article should have been a comic strip. How did it make it on phys.org. The submitter needs to be put on a list that requires at least three sane people to review there submissions.
beyondApsis
4 / 5 (4) Feb 19, 2013
We cannot compare the spatial navigation abilities of the sexes in hunter-gatherer times. Hence we cannot exclude that contemporary differences are just a (random) side effect of settlements.

I would differ. There are a large variety of hunter/gatherer societies currently habitating this planet. Many to choose from.

Any group selected must not be made aware of mapping apps beforehand.
jselin
1 / 5 (1) Feb 19, 2013
While I agree with the message of increased care in determining causes, its not hard to imagine that males select for the vulnerability inherent in the lesser ability.

"don't worry I'll lead you to safety!"
gwrede
2 / 5 (4) Feb 19, 2013
Prof. Rhodes raises an interesting, and seldom discussed issue here. Are some of our traits and properties merely "collateral results" or "side effects" of simply how we are built. And if so, which ones? The question, IMHO, is valid, and I think there just have to be some.

As for cognitive or psychological differences between the sexes, it currently seems trendy to summarily dismiss them. But if we look at animals all the way from simple ants and spiders, to great apes, they have all kinds of gender specific behavior and abilities. And some of them are breathtakingly complex. (Look at the one spider where the male is a herbivore and the female creates intricate webs -- measure his spatial abilities against hers, and you will find a difference, period. Or look at even animals in a zoo, where they have never seen copulation, and they still know what he and she has to do.)

In this light, Rhodes' case against spatial men seems haphazard, and his example species selection unconvincing.
Argiod
3.2 / 5 (5) Feb 19, 2013
Thousands of years with the division of labor being: males go hunting for game, requiring spacial skills; women raise children, requiring communication skills. And this isn't evolution in action?
Scientists can be so blind...
LuckyExplorer
1 / 5 (2) Feb 20, 2013
"... How did it make it on phys.org. ..."

Like many other;-)
Charles ONeal
5 / 5 (1) Feb 20, 2013
Ahhhhhhhhh I have a headache!!!
First it states
""Males' superior spatial ability likely is not an evolutionary adaptation""


That's what the paper is trying to argue - that males' superior spatial ability is likely just a result of increased testosterone, rather than an evolutionary adaptation.


.........then states..........
""is probably "adaptive," meaning that over the course of evolutionary history the trait gave males an advantage that led them to have more offspring than their peers.""


This is the popular hypothesis that the paper is trying to refute. The very next sentence says "A new analysis published in The Quarterly Review of Biology found no support for this hypothesis."


.........then it states.......
""slight, but significant,""


Go learn some statistics. A difference between populations doesn't have to be large to be statistically significant.
geokstr
1 / 5 (7) Feb 21, 2013
There is an easy explanation as to why females have poor depth perception. For their whole lives men have been telling them that this:

================================================)

is nine inches...and they believed it.

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