Evolutionary Just-So Story, Again!


So yet again we have a story of evolution that seems to say that evolution works like God, i.e., that it indulges in design. I am referring to an article recently published in the New York Times reporting on research into why the squid lost its shell. The phrasing of the article will, in the minds of the naive, create the impression that the squid lost its shell in order to move faster to escape its predators (shells being rather heavy and cumbersome). “The evolutionary pressures favored being nimble over being armored, and cephalopods started to lose their shells.” This seems to be an innocent enough statement, but its construction implies that the pressure to become nimble preceded and caused the loss of the shells.

That is design. It may not be God design, though one could easily make that leap, but it is design nonetheless.

Oh, if only they would read Lucretius!

Here’s what really happened: Originally, “squids” we shelled creatures; generation after generation were shelled. Occasionally, a genetic mutation or defect (call it what you will) resulted in progeny lacking shells. No doubt, most of these shell-less individuals quickly died or were eaten and left no progeny; but at some point, some of them survived (perhaps thanks to another mutation that enabled them to move more quickly than their shelled relatives) and reproduced, eventually giving rise to a new class of creatures, squids and octopuses, etc. In other words, the change occurred first, without intention or purpose, and the benefit followed. The change did not occur in order to confer the benefit. It just happened.

Of course, such changes often occur gradually, say by shrinking the shell over many generations, in what some have called “path dependency” (i.e., evolution follows an already established path and does not go backwards, in other words it doesn’t restore the shell to creatures who have lost it). But the principle remains the same: first the change, and then, if it happens to have an advantage, it sticks.

As Lucretius said, humans did not develop opposable thumbs in order to grasp tools; we can grasp tools because we have opposable thumbs.

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