Oh, and on rigid gender roles, I think Jean Auel's Earth's Children book series is where I got the notion that different brains meant different functions. In that series, it is explained that the Neanderthal men and women have very different brains from each other, especially the part that handles memories. It isn't quite "instinct," but it isn't far from it. Therefore, men cannot do women's work, and women cannot do men's work. Not that it is forbidden so much as it is impossible--men don't cook, not because they refuse to, but because they simply cannot learn to. They don't have the brains for it. But then some taboos do end up coming into play. For example, since only men are able to hunt, girls and women are not allowed to touch a weapon, or a tool that would be used to make a weapon. The Neanderthals don't understand why this Cro-Magnon girl even has the desire to hunt, since it wouldn't occur to a Neanderthal woman. I think the book does state that if by chance a girl is born with a memory for hunting, it dies out quickly due to lack of stimulation.

Among the more advanced Cro-Magnons, both sexes can learn all jobs. They'll have men and women hunting side by side, and then going home and cooking their kill together. Homosexuals and transgenders exist among the Cro-Magnons, but not among the Neanderthals.

So this must be where I formed the idea that if men and women have different brains, they'd be locked into rigid roles.