Darwin predicted that the "missing links" of evolution--gaps in the fossil record between related species--would come to haunt his theory. He was right: even today, they're a major theme in the effort to discredit evolution with the public. Which is why there was such a stir about a paper in the journal Nature last week describing a 375 million-year-old creature dug from rocks in the Canadian Arctic. It's a four-foot-long, crocodile-headed fish with scales, gills--and primitive wrist- and fingerlike bones in its fins. Given the Inuit name Tiktaalik, the specimen neatly splits the gap between fossil fish that lived about 385 million years ago and the four-legged amphibians that came 20 million years later.
Until recently, scientists believed that legs evolved when a warming climate dried up ponds and swamps. But Tiktaalik supports the view that legs evolved in water, among fish living in what was then a tropical river delta--perhaps to help them crawl to shallows where larger predators couldn't follow. "It really blurs the distinction between land and water animals," says Neil Shubin of the University of Chicago, who led the team that found the fossil.
Shubin didn't set out to score points for Darwinism, but the implications of his find are obvious: Tiktaalik could turn out to be as iconic as Archaeopteryx, the fossil link between dinosaurs and birds. The Discovery Institute, which promotes "intelligent design" as an alternative to Darwin, was quick to assert that Tiktaalik "poses no threat to [ID] ... Few leading [ID] researchers have argued against the existence of transitional forms." Those "leading researchers" may know better, but the fossil gaps are cited many times in the controversial ID textbook "Of Pandas and People." The book takes particular note of the large difference between "the oldest amphibian" and "its presumed [fish] ancestor." It's a gap wide enough for a fish to walk through--and now we know that one did.