Reproduced by hand from my dead tree copy of *What Technology Wants*:
Old world primates have full-color vision and an inferior sense of smell compared to their distant cousins the New World monkeys…
All, that is, except the howler monkey, which, in parallel to the Old World primates, has tricolor vision and a weak nose. The common ancestor to the howler and the Old World primates goes very far back, so howlers independently evolved tricolor vision. By examining the genes for full-color vision, biochemists discovered that both the howler and the Old World primates use receptors tuned to the same wavelengths, and they contain exactly the same amino acids in three key positions. Not only that, the diminished olfactory sense of both howler and apes was caused by the inhibition fo the same olfactory genes, turned off in the same order and in the same details.
Talk about complex interactions. Is it possible for humans to figure this stuff out? What happens when computers figure this sort of thing out for us?
Bonus, from the previous page:
Biologist Richard Dawkins estimates that “the eye has evolved independently between 40 and 60 times in the animal kingdom… There are only so many ways to make an eye, and life as we know it may well have found them all.