The human hand, with its multi-talented thumb, might be man's greatest tool. But did you know we can trace that thumb, and the hand and arm it's connected to, all the way back to a 375 million-year-old fish named Tiktaalik? This week I sit down with paleontologist and geneticist Dr. Neil Shubin to learn what a fish, and a little blue hedgehog, can teach us about the evolution of thumbs