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This article is from the Lefthanders FAQ, by Barry D. Benowitz b.benowitz@telesciences.com with numerous contributions by others.
40. Why are there more Lefthanded Males than Females?
Recent research has looked at the amount of Testosterone
present in the fetus and amniotic fluid during
pregnancy. Scientists have speculated that an excessive level
of testosterone slows the development of the left side of the
brain, which allows the right side of the brain to achieve and
maintain dominance.
Adult females normally produce a small amount of testosterone
which will find its way into the amniotic fluid during
pregnancy. A male fetus produces some testosterone in the
uterus during development while a female fetus will produce no
testosterone. Therefore, the chances of testosterone
reaching excessive levels are much higher in a male fetus than
in a female fetus simply because the normal levels of
testosterone for a male fetus are higher in the first place.
Males are about one and one half times more likely to be
lefthanded than are females.
Thanks: Gerald McMullon <gerald.mcmullon@ukonline.co.uk>
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