DISCONTINUOUS VARIATIONS 83 



a tree becomes " weeping," a genius is born. It may be useful 

 in such cases, where a new pattern of organisation or a new 

 constitutional property turns up, to speak of a discontinuous 

 qualitative variation. 



Historical Note. — The idea that organic changes might come 

 about by leaps and bounds is not novel, though the evidence 

 substantiating it is quite modern. 



Some of the older evolutionists, such as Etienne Geoffroy 

 St. Hilaire, believed in saltatory evolution, and were far from 

 agreeing with Lamarck that Nature is never brusque. 



Darwin also recognised that big steps may be taken suddenly — 

 e.g. in the origin of large-crested Polish fowls and short-legged 

 Ancon sheep, but he thought that these discontinuous variations 

 occurred rarely, and would be liable to be swamped by inter- 

 crossing. As every one knows, he relied mainly on the action 

 of natural selection on the small, continuous, individual variations 

 which are always forthcoming. 



But the modern appreciation of the importance and frequency 

 of discontinuous variations is mainly due to Bateson, who, in 

 his Materials for the Study of Variation (1894), gave many in- 

 stances of the sudden appearance of offspring which in some 

 particular diverge widely and abruptly from their parents ; and 

 to De Vries, who has observed the occurrence of " mutations " 

 in many plants, and has also followed them through generations, 

 showing that they tend to breed true. 



A Change of Yiew. — Darwin and orthodox Darwinians relied 

 in the main on the operation of selection on small individual 

 variations — many of which are nothing more than quantitative 

 fluctuations. If new adaptations and new discontinuous species 

 arise in this way, the small variations must be heritable, the new 

 character must be capable of cumulative increase by the per- 

 sistent outcrop of similar variations generation after generation, 

 the selection must be persistent and consistent, and a long time 

 must be allowed. 



