Christina Hoff Sommers

Any child may go through periods during which they become less outspoken with their parents or teachers. But girls, like boys, live in many different worlds - they have their friends and their classroom and their parents - and within these different domains, they may have different levels of expressiveness.

If a man made himself an expert in any particular branch of human activity, there would result the strong tendency that a peculiar aptitude towards the same branch would be found among some of his descendants.