The Island of Doubt

Well, not clams. And not legs as such. But there's a neat piece out in Nature on the evolutionary leap, so to speak, between fish fins and the limbs of land critters. A team of researchers has "discovered that the median fin of Catsharks, although originating from different embryonic cells, uses the same genes (Hox and Tbx18) during development as limbs and paired fins."

It's not quite that simple, of course. But before we get to the details, allow me to quote from an AP story that appeared within 24 hours of the announcement of the fin-limbs paper. It's about the Creation Museum that's "rising fast in rural Kentucky." According to John Morris, president of the Institute for Creation Research in San Diego,

"Americans just aren't gullible enough to believe that they came from a fish."

Keep that in mind while you read of the conclusions of a team of biologists at the University of Florida, where the public affairs office decided the research was worthy of a press release:

The earliest vertebrate fossils show only well-developed dorsal and ventral (median) fins what has led researchers to suspect that these were the basis for which all paired fins and limbs evolved. However, their different location (median versus side of the body) seemed to indicate that they appeared from different cells in the embryo, which challenged the common-origin idea. ...

"Given that paired fins made their evolutionary debut at a particular location on the sides of the body, intuitively one would think the genetic tools for fin development would be brought together in that place," said developmental biologist Martin Cohn, an associate professor with the University of Florida (UF) departments of zoology and anatomy and cell biology and a member of the UF Genetics Institute. "We've discovered that the genetic circuitry for building limbs first appeared in an entirely different place -- the midline of the animal.

Because the same developmental mechanism can be found in one of the more ancient species of fish, the lamprey, the researcher also suggest that the mechanism is even older than vertebrates. Gotta love those Hox genes.

Oh yeah. And take that, ye of the missing-link argument.

(Incidentally, I'm aware the headline for this post is taken from a comic strip authored by a evolution denier. Oh, the irony.)