THE STATISTICAL STUDY OF EVOLUTION. 447 



THE STATISTICAL STUDY OF EVOLUTION. 



By Professor C. B. DAVEXPORT, 

 university of chicago. 



AS I was going through the chemical section of the John Crerar 

 Library the other day I stopped to examine two books. The 

 first was one of those dawning-chemical works — Ghiuber's — which en- 

 joyed a wide reputation in the sixteenth and seventeenth centuries. It 

 contained an abundance of speculation and of recipes; but the recipes 

 were of a purely qualitative sort — mix this and this, the amount is 

 immaterial. The second book was the lectures of Van't Hoff, marking 

 the most recent development of the science of chemistry. This book is 

 full of formulae and tables; numbers, signs and quantities fill every 

 page; they are symbols not only of quantitative relations but also 

 of the direction and cause of advance of chemistry since the days of 

 the alchemists. The history of chemistry is the history of the other 

 quantitative natural sciences, of astronomy and physics. As science 

 advances its methods become more and more quantitative. 



Biology is often contrasted with physics and chemistry as a quali- 

 tative science. But there is nothing so fundamentally dissimilar in 

 the phenomena of chemistry and biology that they must necessarily be 

 studied so differently. Both treat of matter, not only statically but 

 also dynamically. But the phenomena of biology are more complex 

 than those of chemistry, the things to be described and compared are 

 more numerous ; and so the science, which is hardly more than a century 

 old, is still in the descriptive and comparative stage. But the history 

 of science in general justifies the prediction that biology, too, will in 

 time use chiefly quantitative methods in studying processes. 



Evolution is an organic process. It has been studied in various 

 ways. Many have sought by ingenious logic to discover its workings. 

 Others have reasoned by analogy from the effects of artificial breeding. 

 Others still, having observed a pro1)able factor of evolution in one case, 

 have argued for its universality. But all of these methods have been 

 qualitative. More recently, on the other hand, there has been under- 

 taken an exact, quantitative study of the condition of species in nature 

 under different environments, to determine exactly the effects that the 

 different environments have produced. This new method, which now 

 demands our attention, is nothing less than the quantitative study of 

 evolution. 



