Re: sexual dimorphism/brains/hormones/development

Ralph L Holloway (rlh2@COLUMBIA.EDU)
Mon, 20 Feb 1995 18:05:10 -0500

Rob Quinlan's post here is sure a welcome relief. Yes, the uterine
enivironment has been shown to be very siignificant factor in
brain-endocrine interactions. More recent stuff on this exists and for
animals other than rats. Good to remember also that humans don't bear
litters, so it is difficult to know how important this is in most single
As for the corpus callosum in human males and females, I would be
very grateful if people following this would read my 1993 AJPA paper.
There is a very high degree of overlap in the absolute size of the corpus
calloum and its posterior splenial portion in males and females. When
corrected for brain weight, there are significant differences between the
means of the male and female values, but still considerable overlap. In
1986, in Human Neurobiology (a journal now out of print) we showed that
there was a significant difference between human foetal corpora callosa
early in the gestation. Some of the literature reviewed in the 1993 AJPA
article addresses (at least speculatively) the brain -endocrine
interaction, i.e., Allen, Gorski, etc.).As for lateralization, yes, there
is considerable overlap among male and females. That is why these results
cannot be applied to individuals in any policy way.
Ralph Holloway.
in the On
Mon, 20 Feb 1995, Rob Quinlan wrote:

> This may not have anything to do with human brains, but I thought
> some of you might be interested anyway. F. vom Saal at the u. of
> missouri did some experiments with the fetal environment of mice.
> He delivered mice pups by caesarean to document their position in
> utero. Males positioned between 2 males (2M) subsequently developed
> aggressive behavior. 0M males (males positioned between two females)
> were less aggressive. 2M females and 0M females had similar out comes.
> I won't go into the details except to say that post natal hormone
> differences were controlled for. The conclusion was that higher levels
> of either testosterone or estradiol (resulting from fetal positioning
> between male or female sibs) either masculinized (under increased
> fetal testosterone levels) or feminized the mice brains (under increased
> fetal estradiol levels). The implication (to me) is that there may
> be a continuum (at least in mice) in neurological feminization/
> masculinization -- female 0M would be the most feminized while
> male 2M would be the most masuclinized. I guess my point is that
> sexual dimorphism in the brain may have a lot to do with environments
> pre- and post-natally. I wonder how much overlap there is between
> male and female humans in terms of lateralization? I.e., are there
> some males that are less lateralized than most, and are there some
> females that are more lateralized than most? What would cause these
> differences?
> Rob Quinlan
> P.S. Although I think it's interesting to discuss cultural differences
> between men and women, I don't see how in the world it can be divorced
> from biology. Therefore, anthropology should try to integrate our
> knowledge rather than drive wedges between camps.
> vom Saal, F. S. et al. 1983 High fetal estrogen concentrations:
> correlation with increased adult sexual activity and decreased aggression
> male mice. _Science_ 220:1306-1309.
> see also Alcock, J. 1989 _Animal behavior_ (chapter 4. development of
> behavior) for a review of vom Saal and other interesting stuff.