Richard Dawkins in New Statesman:
If you have overdosed on Darwin this anniversary year, the great man himself is partly to blame: he was inconsiderate enough to publish On the Origin of Species when he was exactly 50. The resulting coincidence of sesquicen�tennial with bicentennial was bound to excite the anniversary-tuned antennae of journalists and publishers. Anniversaries are arbitrary, of course, dependent on the accident of our having ten fingers. If we had evolved with eight instead, we would have to suffer centenaries after only 64 (decimal) years, and style gurus would prate about the changing fashions of octaves instead of decades.
Incidentally, it is not far-fetched that we might have evolved a different number of fingers. The pentadactyl limb (five digits on each) has become a shibboleth of vertebrate zoology, and even animals such as horses (which walk on their middle fingers and toes) or cows (two digits per limb) have lost the extra digits from a five-fingered ancestor. But the lungfish-like group of Devonian fishes from which all land vertebrates are descended included species with seven (Ichthyostega) or eight (Acanthos�tega) digits per limb. If we were descended from Acanthostega, instead of from an unsung five-fingered cousin of the same fish, who knows what feats of virtuosity pianists might now perform with 16 fingers? And would computers have been invented earlier, because hexadecimal arithmetic translates more readily than decimal into binary?
Historical accidents of this sort are rife, contrasting with the illusion of good design to provide some of our most convincing evidence that evolution happened.
More here.