Re: brain sexual dimorphism [cont'd]

Ralph L Holloway (rlh2@COLUMBIA.EDU)
Fri, 17 Feb 1995 22:50:58 -0500

For whatever it is worth, I have suggested that the differences I find in
the corpus callosum were derived through past evolution for complemental
social behavior that made women more skilled or competent or sensitive to
social behavior, particularly with children and in power relations with
males. Males, I believe, have a slight advantage in visuospatial
integration, but not in social communication. These competencies are no
longer under selection pressures (and probably have'nt been for 10,000
years. The dregree of overlap is almost total, and I regard these things
as evolutionary residua. I've speculated on it in the 1993 Am. J. Phys.
Anthro. article on this dimorphism, and I stress that this highly
R. Holloway.
On Fri, 17 Feb 1995, Daniel A. Foss wrote:

> In the New York Times (Thurs Feb 16) article cited by Ralph L Holloway,
> Gina Kolada, Times science writer, quoted Dr Sally E. Shaywitz, principal
> investigator in the Magnetic Renonance Imaging study which found brain
> sexual dimorphism in phonemic decoding in reading, to the effect that
> there was no evolutionary survival or sexual advantage for the dimorphism,
> considering that males and females performed the decoding task equally well.
> Are all the parts of the latter suggestion equally valid? Might some survival
> or sexual advantage have accrued to males or females at some time in the
> evolutionary past, such as is not evident in the present? Why do males
> outnumber females among the reading-disabled? Is there any possible relevance
> to females outperforming males on standardized tests of language skills? To
> comparative sociolinguistic studies showing that females tend to speak more
> prestigious versions of local languages than do males? To the circumstance
> that mothers typically transmit the phonemic structures of initially-acquired
> languages to nursing infants and small children by age two? What cross-cultural
> patterns, that is, do we already know about that might bear upon the
> *evolution* of brain sexual dimorphism? Any ideas, even wild guesswork, sheer
> supposition, etc, welcome. I'm confused.
> Daniel A. Foss