Saturday, December 31, 2005

How Much of an Explosion was the Cambian Explosion?

A very cool new post on Pharyngula examines new research attempting to work out the phylogeny of animal phyla. As a bonus, there's an important place for fungi in this work -- always a good thing. More on the fungi below.

The researchers compared the sequences of 50 genes in 9 phyla to try to create a family tree. (I am under the impression that this is way more genes than are normally used for systematics. Is this correct?) Some of the branch points could be resolved fine, but it was not possible to distinguish branching times for others. Various modifications, detailed in the Pharyngula post, didn't help. The conclusion? The Cambrian explosion 543 million years ago was quite rapid, so branching times are too close together to be sorted out by the methods used.

As one of their tests of this idea, the investigators tried the same techniques on fungal phylogeny, since fungal evolution appears to lack anything like the Cambrian explosion. Walla! The methods worked just fine, producing a clean and reasonable family tree. This research agrees with the fossil record, suggesting that the Cambrian explosion was a real event.

Now, anyone who can refer to events that took tens of millions of years as an "explosion" is either a geologist or an evolutionary biologist. The term is confusing to laypeople and plays into the hands of creationists. "Rapid adaptive radiation" is too technical, plus the word "radiation" doesn't help. My poetic side wants to borrow Brian Swimme's renaming of the Big Bang and call the event the "animal flaring forth", but that suffers from the same problems as "explosion". How about "animal branching out"?

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