n8 THE POPULAR SCIENCE MONTHLY 



CUBEENT PEOGEESS IN THE STUDY OP NATUEAL 



SELECTION 



By Dr. J. ARTHUR HARRIS 



CABNEGIB INSTITUTION OF WASHINGTON 



I. Introductory Eemarks 



IN papers on " The Measurement of Natural Selection " and " On 

 Assortative Mating in Man," which have appeared in these pages, 1 

 I have endeavored to show by a review of the quantitative work already 

 done that natural selection and sexual selection are not subjects for 

 idle speculation and polemics, or even for inductions from compara- 

 tive evidence, but that, like the other factors of organic evolution, they 

 are open to direct quantitative investigation. 



It is perhaps not too soon to list up for the convenience of those 

 who desire to take a broad view of evolutionary research, the studies 

 in natural selection which have appeared since the first of these papers 

 was written. 



In doing this the ideals of the earlier papers will be carefully 

 maintained. That is, only questions of observed facts and the methods 

 of analyzing them will be taken into account. Theories will be ignored. 

 Again, both positive and negative results will be given impartially, for 

 in the real advancement of science both are of importance in the direc- 

 tion of research and in the formulation of laws. 



It will be conducive to clearness to recognize that two fairly distinct 

 problems confront the student of natural selection. The first is to 

 determine whether in any given case the death rate is random or selec- 

 tive. The second is to ascertain what physical, physiological or psy- 

 chological characteristics make for fitness or unfitness for survival. 

 The attack upon the second problem presupposes the successful solu- 

 tion of the first, for if there be no evidence of the selective nature of 

 the death rate, it is obviously idle to test the selective value of indi- 

 vidual characteristics. It is equally clear that any study which stops 

 short of the second of these tasks is in a high degree unsatisfactory. 

 From the standpoint of evolutionary science it is desirable that the 

 significance for survival in various environments of each type of varia- 

 tion in structure or function should be worked out. But this is a task 

 of the highest difficulty and will probably never be accomplished for 

 more than a few selected cases. In these exceedingly difficult fields 

 practicability must be a primary consideration. In many cases, it may 



*Pop. Sci. Mo., 78: 521-528, 1911; loc. cit., 80: 476-492, 1912. 



