192 EEV. J. T, GITLICK ON DIVERGENT EYOLUTIOIS- 



conditions has power to winnow out whatever forms are least 

 fitted to survive, there will usually remain a number of varieties 

 equally fitted to survive ; and that through the law of segregation 

 constantly operating in species distributed over considerable 

 areas, these varieties continue to diverge both in form and in 

 habits till separate species are fully established, though the con- 

 ditions are the same throughout the whole area occupied by the 

 diverging forms." The conclusion reached was, that " The theory 

 that diversity of Natural Selection is, like variation, an essential 

 factor in producing diversity of species, is untenable. On the 

 contrary, we find that diversity of Natural Selection is not 

 necessary to diversity of evolution, nor uniformity of Natural 

 Selection to uniformity of evolution ; but while variation and 

 separation are the essential factors in diversity, and intercrossing 

 and unity of descent the essential agents in uniformity of evolu- 

 tion, Natural Selection may be an important ally on either side." 



In an article on " Evolution in the Organic World," published 

 in ' The Chinese Eecorder ' (Shanghai), July 1885, I use the fol- 

 lowing language : — " We see what Natural Selection cannot 

 explain by considering the nature of the process. The sur- 

 vival of the fittest results in the separate breeding of the fittest, 

 and therefore in the increasing fitness of successive generations 

 of survivors ; hut how can it account for the division of the survi' 

 vors of one stock, occupying one country, into forms differing more 

 and more widely from each other ? To explain such a result we 

 must find some other law. I am prepared to show that there is such 

 a law rising out of the very nature of organic activities, a law of 

 Segregation, bringing together those similarly endowed, and sepa- 

 rating them from those differently endowed.^'' 



Without Variation there can be no Segregate Breeding ; and 

 without Segregate Breeding and Heredity there can be no accu- 

 mulation of divergent variations resulting in the formation of 

 races and species. In producing divergent evolution, the causes 

 of Variation and Heredity are therefore as important as the 

 causes of Segregate Breeding ; and though I pass them by in my 

 present discussion, I trust it will not be attributed to an under- 

 estimate of their importance. Though I do not stop to discuss 

 the causes of variation, my reasoning rests on the observed 

 fact that in every department of the organic world variation is 

 found, and that in the vast majority of cases, if not absolutely in 

 all, the diversities to which any freely intergenerating group of 



