sexual dimorphism/brains/hormones/development

Rob Quinlan (C611417@MIZZOU1.MISSOURI.EDU)
Mon, 20 Feb 1995 09:43:22 CST

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

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.