cox, DARWIN AND THE MUTATION THEORY 433 



enable them to transform themselves into other groups better adapted to the 

 changing en\aronment. Before Darwin's time every one of course had 

 ocular demonstration of the fact that there were differences between indi- 

 viduals and that descendants were not in every respect like their ancestors. 

 There was universal belief, however, that these variations never extended 

 beyond certain narrow boundaries built round species like inviolable walls. 

 Curiously enough, Darwin, who first broke down these boundaries, took 

 these same individual variations as the principal foundations of his selection 

 theory. He assumed — for he admitted that it could not be proved for any 

 particular case — that these small differences, which ordinarily fluctuate 

 about a certain average for each species or variety, are at times accumulated 

 to such a degree as to carry all the members of the group forward to a new 

 center of oscillation so as to constitute in effect a new group. It was not at 

 first his idea that a single individual, or a small number of incUviduals, might 

 occasionally develop evolutionary force enough to overleap suddenly the 

 imaginary limit and become the nucleus of a new colony beyond; that is 

 the substance of the mutation theory; and, while I think it can be shown 

 that Darwin more or less clearly recognized the possibility of the occasional 

 origin of permanent races by this method of saltation, there can be no 

 doubt that he entertained a strong bias in favor of the evolution of species 

 generally by slow and minu+e steps. 



As far as cultivated plants and domesticated animals were concerned, 

 Darwin was willing to grant the widest range of variation and the most 

 abrupt changes, but as to animals and plants in a state of nature he was 

 more sparing of his admissions that great and sudden departures from speci- 

 fic types might occur. This tenure of the two points of view was due to his 

 belief that domesticated animals and plants were more variable than feral 

 forms, because of the direct influence of man upon their surroundings and 

 habits of life. Inasmuch as his theory of the origin of species through 

 natural selection is founded on analogy between the deliberate operations 

 of breeders in choosing the most desirable individuals of their flocks and 

 gardens, and the inevitable sifting out of feral forms through their competi- 

 tion with one another in the struggle for existence, it is difficult to see why 

 Mr. Darwin hesitated about carrying the comparison to its logical conclu- 

 sion in the admission that what we now call mutations, but what he referred 

 to as "spontaneous variations," "sports," "monstrosities," etc., stand upon 

 substantially the same basis in nature as in cultivation. According to the 

 present-day views of scientific students of animal and plant breeding, I 

 understand, there is no good evidence that cultivated plants and animals are 

 more subject to wide and abrupt variations than are those living under 

 natural conditions. On this point Professor de Vries remarks that "it is 



