When the Explainer asked you to vote on a favorite unanswered question of 2012, the majority opted for a rather lascivious query regarding why rich ladies sunbathe topless, and the Explainer has duly delivered your pound of flesh. But in perusing the runners-up, another question so intrigued the Explainer that he could not resist answering it as well:When and how did humankind figure out that sex is what causes babies? It’s not exactly the most obvious correlation: Sex doesn't always lead to babies, and there’s a long lead time between the act and the consequences—weeks before there are even symptoms, usually. So roughly where do we think we were as a species when it clicked?
