THE ORIGIN OF SPECIES 69 



the vogue of the " preliminary account " was so enormous that 

 it completely overshadowed the full work of which it was 

 meant to be the herald. The general conclusion at which 

 Darwin arrived is that variations, so far as they are inheritable, 

 are due to external conditions acting directly on the germ- 

 cells, and that one external condition which seems to have 

 had a great deal of influence has been the presence of an 

 abundance of food. The efforts of biologists, both zoologists 

 and botanists, since Darwin's time, have been in large measure 

 directed to extending and confirming his work, and a great 

 deal of research has been done with a view to finding out 

 the nature and cause of variations. There is a popular 

 idea abroad that one result of these researches has been to 

 discredit Darwin's theory. It cannot be too strongly stated 

 that such is not the case, and a brief statement of what has 

 actually been accomplished will therefore be in place. At the 

 same time that Darwin published his Origin of Species, 

 Gregor Mendel, an Augustinian monk, was carrying on experi- 

 ments in crossing different varieties of peas, and he arrived at 

 a conception of the laws governing inheritance when two races 

 of the same species were crossed, which has been called Men- 

 delism and which has been largely confirmed by the work of 

 subsequent workers. But these laws only apply to cases 

 where the two races or varieties can be separated from one 

 another by one or more clearly definable characters. Mendel 

 himself expressly stated that he refused to have anything to 

 do with differentiating characters which were of a " more or 

 less " description. Now Darwin was well aware that amongst 

 the domesticated animals such sharply -marked varieties 

 popularly known as "sports" did occur, but for various 

 weighty reasons he did not consider that they had been of 

 importance in the building up of new species ; the kind of 

 variation which he believed has been " laid hold of by natural 

 selection " was precisely that kind of " more or less " difference, 

 i.e. slight differences in the proportion of parts of one animal 

 as compared with those of another, which Mendel left out of 

 account. If this view be correct, Mendel's views, while 

 perfectly justified with regard to the subject-matter to which 

 they were applied, have no relevance to the point at issue. 

 Mendel showed that the hybrid produced by crossing two 



