SallyNow said:
the theory that overall, the male population has a flatter bell curve when it comes to intelligence, meaning that there are more exteremly intelligent genuses (IQ's of over 160) men than women, but also more less intelligent men than women, and that there is higher percentage of highly functioning, midrange to highly intelligent women than men.
This does seem to be the case, a dispropotionately large number of genes that affect intelligence are located on the X chromosome. This means that men are more likely to suffer the harmful effects of mutations in these genes but also benefit from intelligence boosting alleles. In females deleterious alleles could be masked by the other copy but so could beneficial alleles.
From this paper: X-linked genes and mental functioning. David H. Skuse. Human Molecular Genetics, 2005, Vol. 14, Review Issue 1
"Why should there be such a concentration
on this particular chromosome ? Zechner et al. suggest
that the X-chromosome has been engaged in the development
of sexually selected characteristics for at least 300 million
years and that natural selection has favoured the development
of X-linked genes that are associated with higher cognitive
abilities. In particular, males are more likely than females to
be influenced by haplotypes that are associated with exceptionally
high abilities. For an equivalent reason, they are
also more likely to show deficits in mental abilities than
females because of the impact of deleterious mutations
carried in haploid state. The hypothesis offers an explanation
for the higher male variance in many aspects of cognitive
performance."