This Week's Citation Classic

I've finally read Darwin's The Voyage of the Beagle. I put it off since I figured it was mostly of historical interest, and I wouldn't learn anything new. I was wrong. The work is certainly remarkable for its insight and breadth of knowledge.

While the evolutionary ideas are nascent, the book does show the progression of Darwin's thoughts on biological change via natural selection. Most of these thoughts came to Darwin thru revelations from geology.

First is his realization of the age of the Earth. On viewing the granitic formations on the coast of Brazil, Darwin remarks, "Can we believe that any power, acting for a time short of infinity, could have denuded the granite over so many thousands of square leagues?" and later considering the basaltic lava at the Narrows of the Strait of Magellan "we must confess it makes the head almost giddy to reflect on the number of years, century after century, which the tides, unaided by the heavy surf, must have required to have corroded so vast and area and thickness of solid basaltic lava".

Darwin also found a fossilized horse tooth in the Pampas, and commented, "Certainly it is a marvelous fact in the history of Mammalia, that in South America a native horse should have lived and disappeared, to be succeeded in after-ages by the countless herds descended from the few introduced with the Spanish colonies." Darwin was quite aware of the vast number of extinct species whose fossilized remains had been found.

Numerous times Darwin observes slight variations between species spread over geographic areas such as 12 different species of planariae in the southern hemisphere, mice in Chiloean archipelago and, of course, the finches of the Galapagos.

Time plus variation plus extinction must have been a major insight for Darwin. The idea of natural selection must be fermenting when Darwin writes, "When pasture is tolerably long, the niata cattle feed with the tongue and palate as well as common cattle, but during the great droughts, when so many animals perish, the niata breed is under a great disadvantage, and would be exterminated if not attended to; for the common cattle, like horses, are able just to keep alive, by browsing with their lips on twigs of trees and reeds; this the niatas cannot so well do, as their lips do not join, and hence they are found to perish before the common cattle. This strikes me as a good illustration of how little we are able to judge from the ordinary habits of life, on what circumstances, occurring only at long intervals, the rarity or extinction of a species is determined."

The idea of natural selection is crystallized in this paragraph, "The most curious fact is the perfect gradation in the size of the beaks in the different species of Geospiza, from one as large as that of a hawfinch to that of a chaffinch, and (if Mr. Gould is right in including his sub-group, Certhidea, in the main group) even that of a warbler....Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends."

Most of all I was impressed at his vision, even at an early age. "This small family of birds [Tinochorus] is one of those which from its varied relations to other families, although at present offering only difficulties to the systematic naturalist, ultimately may assist in revealing the grand scheme, common to the present and past ages, on which organized beings have been created."

Map from Darwin Day Celebration.