THE 



POPULAR SCIENCE 



MONTHLY. 



JUNE, 1911 



THE MEASUREMENT OF NATURAL SELECTION 



BT Db. J. ARTHUR HARRIS 



STATION FOB EXPERIMENTAL EVOLUTION, COLD SPEING HAEBOB, N. T. 



I. The Status of Darwinism 



BY organic evolution the broad-minded biologist of to-day under- 

 stands merely the natural as opposed to the supernatural proc- 

 esses by which the hundreds of thousands of kinds of organisms which 

 now inhabit or have inhabited the surface of the earth have come to 

 possess the morphological and physiological peculiarities which dis- 

 tinguish them from each other. He believes that these differentiable 

 types have been derived by a natural and relatively gradual process from 

 earlier and, in the main, simpler forms. 



This belief he shares with all his associates ; the evidence in favor of 

 it is considered by scientific men to be so strong that it has become 

 scientific faith and scientific dogma. To-day, only the nature of the 

 processes by which this evolution has proceeded interests biologists. 

 Darwin's theory, and in large measure Darwin's evidence, have accom- 

 plished this. At one time Darwinism and organic evolution were 

 synonyms, but now the suffixes " ian " and " ism " and the prefixes 

 " neo " and " ultra " and " post " are combined with half a dozen dif- 

 ferent names and discussed with a glibness which is bewildering to 

 some of those who are more interested in measuring the intensity of 

 the factors which may have been active in organic evolution than in 

 formulating theories concerning it. 



Darwin's theory, viewed from such a distance that trivial details 

 blend into large outlines, involves three propositions : 



Eirst, that variations from the typical condition of an existing 

 species do occur. 



Second, that these deviations may be inherited. 



Third, that in the competition for existence which must result from 



VOL. LXXVIII. — 37. 



