Geary 3

From: Lyne Kate (
Date: Mon Feb 09 1998 - 15:19:40 GMT

This is my comment and summary of section three of the target article.

[Note: This was the old assignment; so both Lyne Kate and Judy Chatwin
were assigned this section to comment on. -- SH]

Evolution of sexual differences

Having discussed the biological primary and biological secondary
traits in the section, the author then goes on to describe the
evolution of sexual differences. Beginning with the most
fundemental difference between males and females, that is parental
investment, the author claims that:

> Those social and cognitive
> characteristics that might contribute to any sex difference in the
> level of investment in offspring would be examples of germane
> features of the sexual division of labor.

Because males will have less investment in the offspring there is
greater competition to mate with as may females as possible and thus:

> the sex that invests the least in offspring will show less
> discriminant mating, and, relative to the higher investing sex,
> show more intrasexual competition over access members of the
> opposite sex, be physically larger, and have higher mortality
> rates, among other things

Selection will favour those males that are bigger, stronger, less
choosy. The physiological characteristics, will have a large
influence on behavioural and cognitive abilities:

> social behaviors and cognitive abilities that are sensitive to
> fluctuations in hormonal levels are good candidates
> for primary attributes that have been shaped by sexual selection.

> The point is, in terms of mean differences and the ratio of
> extremely aggressive
> males to females, sex differences are expected to be largest in
> evolutionarily significant contexts, such as a threat to status, and
> much smaller in other areas. Nevertheless, these differences might
> influence how boys and girls respond to competitive, as
> contrasted with cooperative, classroom environments.

(This seems to be suggesting that sex differences will be larger in
males in competitive situations. O.k. But is the classroom a true
competitive environment? Ironically social studies indicate that it
is girls who dominate boys in this environment. How is the class room
comparible to the original evolutionary environment of hunting,
fighting etc?? )

> Perhaps related to the above are sex differences in the relative
> degree to which males and females are object versus people
> oriented; males appear to be relatively more object oriented, and
> females more people oriented

This seems would have some bearing on the cognitive ability
differences in males and females. It could be argued however that it
is only a bias and not a direct influence

> It is more likely that the object preferences of boys reflect a bias
> toward learning about the physical, as opposed
> to the social, environment.

While discussing variation within males and females the author quotes
that even individual differences may be influenced by hormones

> Furthermore, "there is now substantial evidence that cognitive
> patterns may vary with phases of the menstrual cycle in normally
> cycling women and with seasonal variations in androgens in men"

The central focus of the argument is:

> The point is---if males with superior spatial
> abilities (which facilitate hunting and, for example, group
> migration or warfare) had even a slight reproductive advantage over
> their low-ability peers, then a sex difference, favoring males, in
> certain spatial abilities (e.g., those involving the processing of 3-
> dimensional information) would have emerged over the course of human
> evolution.

> Whatever the ultimate reason, for humans, it is likely that hormones
> have direct and indirect effects on the development of
> spatial abilities (Geary 1989). Direct effects would include the
> influence of sex hormones on the development of the neural
> substrate that supports spatial cognition (Diamond et al. 1979).
> Indirect influences would involve engagement in behaviors that
> are likely to provide spatial-related experiences to the individual

Thus the conclusion is that sexual selection has selected males that
have a different physiological make up than women and that this may
be related to spatial and arithmetic abilities

Lyne Kate

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