Today’s human population is descended from twice as many women as men.

I think this difference is the single most underappreciated fact about gender. To get that kind of difference, you had to have something like, throughout the entire history of the human race, maybe 80% of women but only 40% of men reproduced.

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For women throughout history (and prehistory), the odds of reproducing have been pretty good. Later in this talk we will ponder things like, why was it so rare for a hundred women to get together and build a ship and sail off to explore unknown regions, whereas men have fairly regularly done such things? But taking chances like that would be stupid, from the perspective of a biological organism seeking to reproduce. They might drown or be killed by savages or catch a disease. For women, the optimal thing to do is go along with the crowd, be nice, play it safe. The odds are good that men will come along and offer sex and you’ll be able to have babies. All that matters is choosing the best offer. We’re descended from women who played it safe.

For men, the outlook was radically different. If you go along with the crowd and play it safe, the odds are you won’t have children. Most men who ever lived did not have descendants who are alive today. Their lines were dead ends. Hence it was necessary to take chances, try new things, be creative, explore other possibilities. Sailing off into the unknown may be risky, and you might drown or be killed or whatever, but then again if you stay home you won’t reproduce anyway. We’re most descended from the type of men who made the risky voyage and managed to come back rich. In that case he would finally get a good chance to pass on his genes. We’re descended from men who took chances (and were lucky).

The huge difference in reproductive success very likely contributed to some personality differences, because different traits pointed the way to success. Women did best by minimizing risks, whereas the successful men were the ones who took chances. Ambition and competitive striving probably mattered more to male success (measured in offspring) than female. Creativity was probably more necessary, to help the individual man stand out in some way. Even the sex drive difference was relevant: For many men, there would be few chances to reproduce and so they had to be ready for every sexual opportunity. If a man said “not today, I have a headache,” he might miss his only chance.