Friday, January 18, 2008

My inner fish!

Alan Cane reviews Neil Shubin's new book at the FT:
Shubin’s basic proposition is encapsulated in what he calls the biological “law of everything”: that every living thing on the planet has parents. This innocuous, quite banal statement conceals a great profundity: that no structure in the living world arises de novo. And not only every creature but also every limb, every organ and every tissue is derived from an earlier form – and in the process, may go through a transformation which renders the relationship between one and the other hard to understand.

He describes, for example, the discovery of the origin of the bones of the mammalian middle ear. Comprising three separate bones, the malleus, the incus and the stapes, this structure is unlike that of any other class of animal: reptiles and amphibians have one bone while fish have none. So where, Shubin asks, did our middle-ear bones come from? The answer was provided in 1837 by the German anatomist Karl Reichert. He had been following the development of gill arches, swellings around the base of the embryonic head, in mammals and reptiles. He was astonished to find that two of the ear bones in mammals corresponded to pieces of the jaw in reptiles. Shubin writes: “The conclusion was inescapable: the same gill arch that formed part of the jaw of a reptile formed ear bones in mammals. Reichert proposed a notion that even he could barely believe – that parts of the ears of mammals are the same thing as the jaws of reptiles”.

As a fossil hunter, Shubin distinguished himself by leading an expedition to the Arctic in 2004 which uncovered the remains of a fish with a wrist, a creature with part fin, part limb. Named Tiktaalik (Inuktitut for “large freshwater fish”), it was the first fossil to show characteristics which placed it midway between land and sea; in its time, Tiktaalik probably propelled itself along the bottom of streams and ponds or navigated mudflats along the riverbank, supporting its body on its strange, limb-like fins.
Here's the Amazon link for Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body.

(Someone at the FT is an undercover fish-lover, eh?!? That paper has been a cornucopia of fish- and water-related stories in the last six months!)

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