591.15 50 [July 



VII 



Karl Pearson on Evolution * 



THE belief that the fundamental problems of organic evolution 

 are essentially statistical problems, which require numerical 

 treatment before they can be adequately solved, is constantly gain- 

 ing ground ; and with the growth of this belief the need for finer 

 methods of statistical inquiry has grown also. With the exception 

 of Mr Francis Galton, who worked for years almost alone in this 

 direction, no one has done so much as Professor Pearson to make 

 the systematic investigation of animal statistics possible. His 

 development of the theory of Chance enables us now to find fairly 

 simple mathematical expressions, by which masses of statistics, 

 hitherto incapable of arrangement in such a form that the mind 

 could grasp their meaning, may be easily and accurately represented. 

 Professor Pearson devotes four of the essays in his recently-pub- 

 lished volumes to a popular account of some of his results. 



The first essay (" The Chances of Death ") begins by showing 

 how regularly " chance " is seen to operate, when a large series 

 of fortuitous events can be observed. The regular character of 

 such events, and the accuracy with which they can be predicted 

 in the long run, is illustrated by records of experiments of the 

 usual kind with coins, dice, and cards ; and it is then shown that 

 a law of the same form as that used to express the result of a long 

 series of games of chance may be used to express, with the same 

 degree of accuracy, the frequency with which given magnitudes 

 of a cephalic index occur in a race of men, or the frequency of 

 patients of given age among a large group of typhoid fever cases. 

 Finally, the frequency of incidence of death at various ages among 

 every thousand people born at the same time is exhibited as the 

 resultant of five series of fortuitous events, each series producing 

 its maximum death-rate at a particular period of life. 



These examples are admirably fitted to show how such appar- 

 ently irregular phenomena as death, or attacks of fever, or variation 

 in the dimensions of a particular organ, may be easily and accu- 

 rately represented so that the mind can grasp the effect upon the 

 population as a whole, grouping the series of isolated instances 



* The Chances of Death, and other Studies in Evolution. By Karl Pearson. 2 vols, 

 8vo, pp. xii. 388, and iv. 460. London: Edward Arnold, 1897. Price, 25s. 



