Thursday 5 September 2013

Human sexual dimorphism (fat-free mass difference between men and women) is greater than generally believed - similar to gorillas!


Extracted from a review article by David A Puts of Penn State University - "Beauty and the Beast: mechanisms of sexual selection in humans." Evolution and Human Behavior 2010; 31: 157-175. Words in square brackets [ ] are my editorial additions, three dots ... represents a cut. References are omitted. Bold emphases have been added.  


Men are larger, stronger, faster, and more physically aggressive than women - and the degree of sexual dimorphism in these traits rivals that of species [such as gorillas and common chimpanzees] with intense male contests.

1. The relatively modest 8% stature [height] dimorphism  in humans... and a difference of about 15-20 % in body mass might suggest that male contests are reduced compared with our closest [primate] relatives. However... this is partly because women are unique among primates in having copious fat stores.

2. When fat-free mass is considered, men are 40% heavier... and have 60% more total lean muscle mass than women.

3. Men have 80% greater arm muscle mass and 50% more lower body muscle mass...

4. ...The sex difference in upper-body muscle mass in humans is similar to the sex difference in fat free mass in gorillas..., [which are] the most sexually dimorphic of all living primates. (...)



JP said...

But hey there's no reason women can't be great police officers, firefighters, and military troopers!

Even if they are scared of cows.

But although Mr Williams was apparently struggling to breathe, when the emergency responder turned up she carried out a risk assessment and decided it was too dangerous to go straight to his side. Instead, she remained in her car until fire fighters arrived to cut open the locked gate into the field so she could drive her car in. This way she would be able to retreat to her vehicle if the cows “became agitated further,” the ambulance service said.

(The "dynamic risk assessment" -- "oh no, there are COWS!")

Bruce Charlton said...

@JP - At another point this review stated that (although male and female strengths overlap) the average man was stronger than 99.9 percent of women.

His general point is that humans give the appearance of having undergone the kind of natural selection by violent male conflict which is seen in gorillas. And that there was not much role for female choice - the men who won the violent conflict got the women...

On the other hand... see the adjacent posting for the view that parental choice was primary.

Both articles suggest that the modern scenario of courtship and couples choosing each other may be an historical anomaly.

JP said...

this review stated that (although male and female strengths overlap) the average man was stronger than 99.9 percent of women.

A fact readily observable to anyone who has ever visited a gym, and yet to say so elicits immediate punishment from the Left.

Kent G. Budge said...

In a modern context, the snappy rejoinder is that what matters more is the relative amount of fat stored between the ears.

I do not think the same way my wife does, notwithstanding we both have graduate degrees in hard sciences. I doubt it is a matter of different levels of intelligence. It would be nice, though, to have more than anecdotal observations on this interesting topic.

Bruce Charlton said...

@KJB - The question of men versus women on 'g' or general intelligence has more than a century of good research

My personal view is that the distributions of intelligence vary between samples - but that it is impossible (on biological grounds, given differences in brain size, composition and development including hormones) that men and women could have identical intelligence. Probably in most populations men have a slightly higher average intelligence, with a wider distribution - a higher proportion of the highest intelligence and more of the lowest intelligence.

jgress said...

I thought Arthur Jensen's research showed that men and women did have the same average IQ. What do you mean that it's impossible for them to be the same? Do you mean in the trivial sense that they can't be exactly identical? No doubt, but surely what matters is whether any difference is significant.

How robust is the correlation between brain volume and IQ?

Bruce Charlton said...

jgress - the commenter asked for my evaluation, and that was what I gave! I think Jensen was wrong - not statistically, but in his null hypothesis that men and women should be assumed to have the same intelligence unless proven different - biologically, this is nonsense.

Two things as different as a man and woman's brain, which are differently composed, and 'made' is different biological environments for different purposes - should not be assumed to be the same in a quantitative attribute like intelligence.

(Most IQ researchers are not biologically minded, nor even medically minded - but psychometricians - and this has been a long-term and still remaining flaw in the field, in my opinion.)

Common sense says that sex differences in intelligence (seen in terms of speed of learning and analysis of abstract systems) are significant, in some situations.

BUT on the other hand intelligence differences are not so important in so many situations as the sex differences in personality, and some of the other cognitive skills (visuospatial, for instance) - which are much more different between men and women than is intelligence.