Wednesday, June 24, 2009

The Best Answer Yet: Which Came First - the Chicken or the Egg?"

I love this. This is exactly why I love reading evolutionary biology...

Author Nick Lane, in his spectacular book Oxygen: The Molecule That Made The World, punctuates a discussion about the evolutionary history of aging with a brief segway, in which he answers the question "Which came first - the chicken or the egg?"

"The first chicken, of course, did not appear suddenly: there was a gradual transition from non-chickens (actually, the red jungle fowl Gallus gallus) to domestic chickens. The eggs of earlier birds therefore evolved before chickens. Eggs with hard shells were in fact invented by the reptiles, around 250 million years ago. After the Carboniferous, the climate grew cooler and drier, and the great coal swamps dried up. The first reptiles developed scales and shelled eggs to escape the constraints suffered by amphibians, which depend on water. Eggs with shells could be laid on land and did not dry out. This was the beginning of the 'age of reptiles', which lasted until the demise of the dinosaurs 65 million years ago. As a related historical accident, the hard shell made copulation necessary. The shell forms before the egg is laid, so fertilization has to take place internally. Thus, all reptiles copulate, and passed on this trait to their descendents -- the birds and mammals. A little understanding of the history of life, then, tells us that both copulation and eggs came before chickens -- and the historical narrative makes the idea of infinte regression seem absurd."

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