PARENTING
01/30/2013 01:06 pm ET Updated Apr 01, 2013

Remaining Puzzle #12: Why Do People With Many Siblings Have Many Children?

For the last six years, I have been compiling a list of empirical puzzles that evolutionary psychology cannot yet solve.

It began with the concluding chapter in our book Why Beautiful People Have More Daughters. In it we admitted that, as great as evolutionary psychology was at explaining the mysteries of human behavior, there were a few things that it could not yet explain. We began with the remaining puzzles that Robert Wright listed in the conclusion of his 1994 book The Moral Animal, which is the book that introduced me to evolutionary psychology so many years ago:

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