DARWINISM AND EVOLUTION DEFINED. 19 



the de Vriesian evening primroses to show that I know my 

 list of classic possible exceptions to this denial of observed 

 species-forming, and to refer to Weldon's broad-and 

 narrow-fronted crabs as a case of what may be an observa- 

 tion of selection at work. But such a list, even if it could 

 be extended to a score, or to a hundred, of cases, is ludicrous 

 as objective proof of that descent and selection, under 

 whose domination the forming of millions of species is sup- 

 posed to have occurred. The evidence for descent is of 

 satisfying but purely logical character; the descent hypoth- 

 esis explains completely all the phenomena of homology, of 

 palasontological succession, of ontogeny, and of geographi- 

 cal distribution; that is, it explains all the observed facts 

 touching the appearance in time and place on this earth of 

 organisms and the facts of their likenesses and unlikenesses 

 to each other, and this no other theory does. The evidence 

 for the selection theory we shall refer to in detail in the suc- 

 ceeding chapters, so we may merely recall now that it also 

 chiefly rests on the logical conclusion that under the 

 observed fact of over-production, struggle is bound to 

 occur; that under the observed fact of miscellaneous varia- 

 tion, those individuals most fortunate in their variations will 

 win in the struggle; and, finally, that under the observed 

 fact of heredity, the winners will transmit to their posterity 

 their advantageous variations, all of which inter-acting facts 

 and logically derived processes will be repeated over and 

 over again, with the result of slow but constant modification 

 of organic types, that is, formation of new species. In the 

 light of this subjective character of the evidence for descent 

 and selection, it is with unusual interest that one notes the 

 swift development of experimental and statistical investiga- 

 tion in biology. Experiment and statistics are capable of 

 mathematical treatment; biology may become an exact 

 science instead of one solely of observation and induction. 

 As with the conclusion of this chapter we are practically 



