The Making of the Fittest
Other have commented on Carroll's example of icefish. I was more struck by his use of our trichromatic vision (ability to see three colors - in our case: red; green; and blue). Most mammels have dichromatic vision. But the Old World monkeys and their descendants (including us) developed trichormatic vision. How? Apparently one of the two color genes was accidently duplicated by mutation, and then the two were tuned to different frequencies of light (green and red). He shows which of the original two was duplicated, and then how the tuning process worked. He does this all at the genetic and chemical level.
Interestingly, most New World monkeys have dichromatic vision, indicating that the mutation occurred after New and Old World monkeys split. But one small subset of the New World monkeys has trichromatic vision. But it is genetically different from ours - indicating that it evolved separately.