(3 of 3)
It all depends on how and when the genes are turned on by a segment of DNA that acts like a switch. Fish have a version of that switch too. For example, Zebrafish (ray-finned fish that split off from the lineage that led to lobe-fins early in the Devonian) have only part of the sequence, whereas coelacanths (lobe-fins closely related to lungfish) have a lot more of it. And the fishapod, presumably, had even more.
None of that comes as a surprise to most biologists. Even the scientists who invoke "intelligent design" to explain life's diversity concede that transitional creatures have been showing up in the fossil record for quite some time. "The argument that there are no transitional forms," says Kenneth Miller, a Brown University biologist and staunch defender of evolution, "has been untenable for at least two decades."
But the lack of missing links is still part of the antievolution rhetoric circulating on the Internet. "Some people will never be convinced," says paleontologist Michael Novacek, provost of science at the American Museum of Natural History in New York City (see box). "But discoveries like this are valuable because there are people who are still undecided about evolution. This gives us an opportunity to educate them." And if not with this discovery, then maybe with the next one. "The fishapod," says Miller, "is one more piece of a rapidly filling jigsaw puzzle. And every couple of years, we put another important piece in place."
[This article consists of a complex illustration. Please see hardcopy of magazine.] Source: Neil Shubin, University of Chicago 380 million years ago BEFORE TIKTAALIK Lobe-finned fish had forelimbs suitable for moving in water but not on land 375 million years ago TIKTAALIK The forelimbs had the beginnings of fingers and a wrist, wrapped inside a fin 360 million years ago AFTER TIKTAALIK Tetrapod forelimbs have wrists and digits used for crawling on land [This article consists of a complex illustration. Please see hardcopy of magazine.]
A LONG WALK The fishapod represents a crucial step in the progression from sea creatures to land animals to, eventually, humans
Source: The Book of Life by Stephen Jay Gould (Norton; 2001) 600 million of years ago - 0
Proterozoic • First shellfish and corals Cambrian Ordovician • First fsh Silurian • First land plants Devonian • Tiktaalik • First tetrapods Carboniferous • First reptiles • First mammal-like reptiles Permian Triassic • First dinosaurs • First mammals Jurassic • First birds Cretaceous • First flowering plants Cenozoic • First horses • First monkeys • First apes • First modern humans