For most of human history, we didn’t know where babies come from. Sure, we knew it involved sex, but beyond that, things got a little fuzzy. The story of how we got clarity on the birds and the bees is as circuitous as it is strange. Its cast of characters includes kings, philosophers, sea urchins, and the father of microbiology. Science writer Edward Dolnick, author of the new book “The Seeds of Life,” tells the tale.