Smart and SeXy: The Evolutionary Origins and Biological Underpinnings of Cognitive Differences between the Sexes

by Roderick Kaine

In addition to rapid evolution made possible by hemizygous exposure in males, an XY system also provides the advantage of obligatory inter-change of brain related genes between the sexes which should lead to greater harmony between sexes in behavior and cognition than might occur in birds. If intelligence is mainly favored in only one sex, then the other can essentially be dragged along in the evolution of higher intelligence.80

I don't follow this argument

80 % of women that lived in the past have modern descendants, but only 40 % men of the past have such descendants.1