Inquiring Minds

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. &