10 November 2007

Little bones, big inference

Early one morning on the way to Heathrow Airport, a taxi driver challenged me to tell him what I thought was the single best evidence for evolution. The first thing to pop into my head was: what, before coffee?

Then, as my caffeine-deprived neurons groaned to life, a second thing came to mind: despite having no legs, nor any need for legs, dolphins and whales nevertheless have itty bitty legs and pelvic bones buried, useless, under mounds of blubber. These rudimentary legs and pelvises are called vestigial structures; they are relics of the whales' common ancestry with their legged cousins.

The taxi driver seemed intrigued, but, as Heathrow loomed closer, I could see that he was not going to be convinced. Gosh, I thought, if only I had a handy dandy photo of whale pelvises that I could whip out on just such occasions. Surely such a prop would deftly banish those pesky whiffs of creationist stubbornness that tend to linger at the ends of such conversations. If only... If only...

Well, warm up your inkjets, my friends, because today, in a New York Times slide show called "Bred in the Bone", I found THIS:

Photo: Patrick Gries/Oceanographic Museum, Monaco

Meet the striped dolphin, Stenella coeruleoalba. More to the point, squint your eyes and meet the striped dolphin's vestigial pelvis and legs. They are the small but unavoidably present bones you can see in the photo above, floating in space precisely where fully developed pelvis and legs would have been were the dolphin not so well adapted to its liquid environment.

At this stage I could go on and on about developmental constraints and common descent, but I'll never do it justice the way Thomas Henry Huxley did nearly 150 years ago, when he wrote in his Times review of Darwin's On the Origin of Species...:
"No adaptive reason whatsoever can be given for...rudimentary teeth, which are never used, in the gums of the young calf and in those of the foetal whale; insects which never bite have rudimental jaws, and others which never fly have rudimental wings; naturally blind creatures have rudimental eyes; and the halt have rudimentary limbs. So, again, no animal or plant puts on its perfect form at once, but all have to start from the same point, however various the course which each has to pursue. Not only men and horses, and cats and dogs, lobsters and beetles, periwinkles and mussels, but even the very sponges and animalcules commence their existence under forms which are essentially undistinguishable; and this is true of all the infinite variety of plants. Nay, more, all living beings march side by side along the high road of development, and separate the later the more like they are; like people leaving church, who all go down the aisle, but having reached the door some turn into the parsonage, others go down the village, and others part only in the next parish."
Touche, taxi man.

For more pictures elegant black and white skeletons to wave at evolution skeptics, visit the NY Times slide show or better yet, buy a copy of the book, Evolution in Action. For Steve Jones' take, see my previous post here. For an excellent, in depth essay on how whale pelvises confound creationism, be sure to read Ev Cochrane's On Whales Legs.

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