Friday, September 26, 2008

Fishy Fingers And Why Paleontology Is Sooo Important

From my Science Daily Feed:

Tetrapods, the first four-legged land animals, are regarded as the first organisms that had fingers and toes. Now researchers at Uppsala University can show that this is wrong. Using medical x-rays, they found rudiments of fingers in the fins in fossil Panderichthys, the “transitional animal,” which indicates that rudimentary fingers developed considerably earlier than was previously thought.

Source: Uppsala University

Taxa ancestral to tetrapods had already evolved digits. They were re-sculpted and molded by evolution to serve new functions in tetrapods. So far nothing too surprising. As Francois Jacob had long observed, evolution is a tinkerer, adept at rejigging available parts to serve a different function.

But this is what caught my eye:

When they examined genes that are necessary for the evolution of fins in zebrafish (a ray-finned fish that is a distant relative of coelacanth fishes) and compared them with the gene that regulates the development of limbs in mice, researchers found that zebrafish lacked the genetic mechanisms that are necessary for the development of fingers. It was therefore concluded that fingers appeared for the first time in tetrapods.

Palaeontology gave us an insight on how evolution works that genetic techniques did not anticipate. Some time back Olivia Judson wrote an article on how the new fields of molecular genetics and evolutionary developmental biology are providing insights into the details of evolution that fossils cannot provide. I agreed with much of what she had to say. These methods are revealing the innards of the evolutionary process. But I don't agree that this somehow relegates paleontology to a bit player, a support role to the main actors in evolutionary science. This finding is a case in point.

I like to think of it this way. Let's say Mr. Bill Gates writes an article on how he became rich. But for reasons of whimsy he provides only a log showing the important financial benchmarks of his career. How much money he had in his account at various stages, some selected details of his stock holdings etc. Now, in a technical sense he has told us how he became rich, and from this log we can infer up to a point on the important events of his career. But we don't get a complete picture. The evolution of Mr. Gates from a college dropout to a very successful businessman took place in the context of a human ecology. Who were his childhood influences and his mentors? What did he learn from his interactions with his peers? How did the existing computer industry environment influence his decisions? All this makes for deeper insights and a more complete story of how he became rich.

Paleontology and fossils provide just such a broad ecological context to understanding evolution. When did a particular morphological trait arise? Just how did one morphological form get transformed through successive stages and how does this correlate to functional and ecologic shifts? At what rates did morphological features change? What long term patterns of morphological stasis or changes do particular lineages show? What was the nature of faunal turnovers at mass extinctions? What patterns of evolution do the survivor taxa show? Myriad such details that genetic techniques have little to say about and where paleontology is the primary source for understanding the history of life.

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