And a quirky anecdote:

A little while ago, I listened in on DS8, DS6 and a friend who were discussing how far back up the evolutionary chain you'd have to go to hopefully have a given species evolve into a unicorn. DS8 argued you'd in fact have to go right back to the Big Bang instead of somewhere up the chain, since that would surely be the point at which the universe would need to take a turn in order for unicorns to develop their magical powers.