The Idea of Evolution. 25& 



whatever was not used. In that way they could explain a great 

 many important points which were difficult to understand. For 

 instance, one toe of the horse was developed enormously, and 

 the other four toes which were not used had become starved 

 and disappeared, because all the nourishment went into that 

 one toe. That was a very important variation, and one that had 

 never received in this country all the attention it deserved. It 

 showed you at once how useless things would disappear, and 

 it was also important for this reason that it brought clearly out 

 the resemblance between the animal or plant's body, and the 

 whole mass of individuals that made up a plant species. The 

 disappearance of what was useless in the body of the plant was 

 thus exactly similar to the disappearance of a useful species. 

 The next point was one of those curious drawbacks or objections 

 that constantly came up as if they were a sort of rebellion 

 against the calm progress of scientific inquiry. That was the 

 hybrid idea. People began to remark that hybridising gave a 

 simpler explanation of evolution than those Darwinian ideas. 

 That was all very well, but supposing they crossed two species 

 then each species was tuned to the special conditions of the place 

 in which it lived. The product hybrid of these two species 

 would possibly be in harmony with the environment, and as a 

 matter of fact hybrids, though common enough — for instance, 

 the willows and others in this country were chiefly hybrid — 

 did not seem able to breed and hold their own ground in 

 the way that ordinary species did. Again, it had been recentlv 

 shown that there was a curious tendency amongst hybrids to 

 turn back either to one or to the other ancestral form. Accord- 

 ing to Mendel's law in the case of one dominant character, one- 

 fourth would be the weaker character pure, one-fourth would 

 be the stronger character pure, and one-half would be mixed 

 with both strains in the blood. Here again was a vast oppor- 

 tunity for those who were interested in experimental work of 

 that sort. The fourth great advance was associated with the 

 names of Galton, Pearson, and others. This was the study of 

 variation of the normal variation in one species. This was 

 a mode or fashionable number or length for e\'ery character 

 in a species, but abnormal individuals were exceedingly common. 

 A very curious case was that of the 7 -leaved clover, which was 

 artificially produced by De Vries, who found plants of clover 



