82 2 POPULAR SCIENCE MONTHLY. 



to case, till men whom no power of abstract argument could 

 convince were convinced by pure force of successive witnesses. 

 They were borne down by numbers. Your ordinary English- 

 man, indeed, is never quite satisfied by Euclid's demonstration 

 that in a right-angled triangle the square on the hypotenuse is 

 equal to the sum of the squares on the two opposite sides; he 

 honestly believes it when he sees it tried a hundred and twenty 

 times by careful measurement, and still more when he finds that 

 engineering works which take it for granted as a basis succeed in 

 paying a satisfactory dividend. Proof that in the nature of tri- 

 angles this truth is involved he does not regard ; experimental 

 verification, or what seems to be such, in a few concrete cases, 

 amply satisfies him. Hence it came about that a world which 

 would have listened coldly to Herbert Spencer's a priori reason- 

 ings or splendid generalizations was converted at once when 

 Darwin brought up with inexhaustible patience and extraordi- 

 nary keenness of insight his profound array of confirmatory facts 

 about bees and cuckoos, about the fertilization of orchids and the 

 movements of tendrils. 



Nobody has better summarized than Mr. Clodd the exact point 

 which evolutionary theory had reached as regards plants and ani- 

 mals before the publication of The Origin of Species. Whoever 

 wishes to learn just how much was surmised by the predecessors 

 of Darwin, and just how much Darwin added to their ideas, can 

 not do better than consult his luminous exposition. 



Once, indeed, no less than seven years before the publication of 

 The Origin of Species, Mr. Spencer even trembled for a moment 

 on the verge of the actual discovery of natural selection. This 

 was in the essay on population in the Westminster Review in 

 1852. The passage at full is too long to extract ; but I will quote 

 the last words of it. " All mankind subject themselves more or 

 less to the discipline described ; they either may or may not ad- 

 vance under it ; but in the nature of things only those who do 

 advance under it eventually survive. For, necessarily, families 

 and races whom this increasing difficulty of getting a living 

 which excess of fertility entails does not stimulate to improve- 

 ments in production . . . are on the high road to extinction ; and 

 must ultimately be supplanted by those "\vhom the pressure does 

 so stimulate. . . . And here, indeed, it will be seen that prema- 

 ture death, under all its forms, and from all its causes, can not 

 fail to work in the same direction. For as those prematurely 

 carried off must, in the average of cases, be those in whom the 

 power of self-preservation is the least, it unavoidably follows that 

 those left behind to continue the race must be those in whom the 

 power of self-preservation is the greatest, must be the select of 

 their generation." Now, this is the doctrine of natural selection, 



