How’s this for a coincidence? Charles Darwin and Abraham Lincoln were born in the same year, on the same day: Feb. 12, 1809. As historical facts go, it amounts to little more than a footnote.

As soon as you do start comparing this odd couple, you discover there is more to this birthday coincidence than the same astrological chart (as Aquarians, they should both be stubborn, visionary, tolerant, free-spirited, rebellious, genial…