We all know the Darwin fish, the clever car-bumper parody of the Christian "ichthys" symbol, or Jesus fish. Unlike the Christian symbol, the Darwin fish has, you know, legs. Har har.
But the Darwin fish isn't merely a clever joke; in effect, it contains a testable scientific prediction. If evolution is true, and if life on Earth originated in the oceans, then there must have once been fish species possessing primitive limbs, which enabled them to spend some part of their lives on land. And these species, in turn, must be the ancestors of four-limbed, land-living vertebrates like us.
Sure enough, in 2006, scientists found one of those transitional species: Tiktaalik roseae, a 375 million-year-old Devonian period specimen discovered in the Canadian Arctic by paleontologist Neil Shubin and his colleagues. Tiktaalik, explains Shubin this week’s episode, is an "anatomical mix between fish and a land-living animal."
"It has a neck," says Shubin, a professor at the University of Chicago. "No fish has a neck. And you know what? When you look inside the fin, and you take off those fin rays, you find an upper arm bone, a forearm, and a wrist." Tiktaalik, Shubin has observed, was a fish capable of doing a push-up. It had both lungs and gills. It's quite the missing link.
On the show this week, we talk to Shubin about Tiktaalik, his bestselling book about the discovery, Your Inner Fish: A Journey Into the 3.5 Billion Year History of the Human Body, and the recently premiered three-part PBS series adaptation of the book, featuring Shubin as host who romps from Pennsylvania roadsides to the melting Arctic in search of fossils that elucidate the natural history of our own anatomy.
This episode also features a discussion of the growing possibility of an El Nino developing later this year, and the bizarre viral myth about animals fleeing Yellowstone Park because of an impending supervolcano eruption.