Page:Popular Science Monthly Volume 78.djvu/543

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MEASUREMENT OF NATURAL SELECTION

the next ten years ought to see a material advance in our knowledge of the least investigated of the Darwinian principles.

Studies of Vertebrates.

The relative ease with which large numbers of individuals can be secured and observed is an ample explanation of the fact that practically all the studies of selective elimination have been made on invertebrates.

To Dr. H. C. Bumpus belongs the credit of the first effort to determine whether the death rate among vertebrates may depend in some degree upon the measurable physical characteristics of the individual. Indeed, in the attempt to apply quantitative methods to the problem of natural selection Bumpus[1] was a close competitor for priority with Professor Weldon. His statement of the problem, like that of Professor Weldon, is beautifully clear:

A possible instance of the operation of natural selection, through the process of elimination of the unfit, was brought to our notice on February 1 of the present year (1898), when, after an uncommonly severe storm of snow, rain and sleet, a number of English sparrows were brought to the anatomical laboratory of Brown University. Seventy-two of these birds revived; sixty-four perished; and it is the purpose of this lecture to show that the birds which perished, perished not through accident, but because they were physically disqualified, and that the birds which survived, survived because they possessed certain physical characters. These characters enabled them to withstand the intensity of this particular phase of selective elimination, and distinguish them from their more unfortunate companions.

From his measurements of various bodily dimensions Professor Bumpus concluded that the birds which perished were actually differentiated from those which survived. Some of the differences, however, are so small that to the cautious statistician this attempt to measure the influence of a selective death rate on the type of a population of birds living in a state of nature seems suggestive rather than finally conclusive.

This must not be read as a criticism of Bumpus's work, for he not only saw the problem and the possibility of applying the new methods to it, but he also gave us the full results from an unusual opportunity.

First and last, considerable has been written concerning natural selection in man. Most of the arguments are purely general or specu-

  1. Bumpus, H. C, "The Elimination of the Unfit as Illustrated by the Introduced Sparrow, Passer domesticus," Biological Lectures from the Marine Biological Laboratory, Woods Hole, 1908, pp. 209-226, Boston, 1899. For further statistical constants calculated from Bumpus 's data see a note entitled, "A Neglected Paper on Natural Selection in the English Sparrow," Amer. Nat., May, 1911, p. 314-318.