Sean Carroll in Preposterous Universe:
“What good is half a wing?” That’s the rhetorical question often asked by people who have trouble accepting Darwin’s theory of evolution by natural selection. Of course it’s a very answerable question, but figuring out what exactly the answer is leads us to some fascinating biology. Neil Shubin should know: he is the co-discoverer of Tiktaalik Roseae, an ancient species of fish that was in the process of learning to walk and breathe on land. We talk about how these major transitions happen — typically when evolution finds a way to re-purpose existing organs into new roles — and how we can learn about them by studying living creatures and the information contained in their genomes.