When Did Our Early Ancestors Figure Out Sex Makes Babies?

The most popular question of 2012 on Slate's "The Explainer" was "Why do rich ladies sunbathe topless?" After that important exercise in investigative journalism was completed, Slate doubled back to answer another high-ranked question that's a modicum more interesting, although the interested parties could probably just… » 1/12/13 4:30pm 1/12/13 4:30pm