IF a man wants to have smart sons, his best bet is to marry a smart woman, says Australian geneticist Gillian Turner. Smart men may be bright because of genes they inherit from their mothers, she writes in The Lancet. According to a growing body of evidence, several genes which determine intelligence appear to be located on the X chromosome, the chromosome which men inherit from their mothers. Any mutation on this intelligence gene either for extreme intelligence or mental retardation will be inherited by the male offspring, but not necessarily by the females.
Women also inherit genes for intelligence on X chromosomes, but because they inherit two X chromosomes one from their fathers and one from their mothers any mutation tends to be diluted. Men, however, get the full impact of the gene, which could explain why men suffer mental retardation more often and also why some men are extraordinarily intelligent, Turner believes.