When it was found that the average weight of a man's brain is greater than that of a woman's, this was held as proof of his superior intellectuality. When it was pointed out that an elephant's brain is even heavier, the eminent scientists scratched their heads since they could not admit that their wits were elephantine. Somebody suggested that the important thing is the proportion of the weight of the brain to the weight of the body. But this had a disastrous result: it seemed to show that women were, on the whole, cleverer than men. This would never do. So they said that it was not mere brute weight that mattered but delicacy of organisation. As this was still a matter conjecture, it could be assumed to be better in men than in women.
Source： Are men of science scientific? Feb. 24th, 1932, in Mortals and Others；Bertrand Russell's American Essays 1931-1935, v.1, 1975.