CONCLUSIONS 369 



to indicate if the two theories above mentioned are to be 

 reconciled or if one or the other is inadequate. 



There appears to be no reason to question the orthodox 

 and, indeed, inescapable x contention that evolution has taken 

 place by a series of changes similar in dimensions to the 

 differences in individual characters between races and species. 

 It is possible that changes of an adaptive kind have arisen 

 through mutations occurring en bloc (Chapter VI) ; but at 

 present there is little evidence to support this belief. 



Two features of this process impress themselves on our 

 attention — the origin of groups of various kinds and the produc- 

 tion of adaptations. We are led to contrast the continuous 

 development of small divergences of the order of geographical 

 races, colonies, subspecies and species with the sustained 

 episodes in the course of which complex organs, protracted 

 adaptive modification and the cumulative organisation of 

 parts are established. According to one view these two 

 features are different expressions of one and the same process ; 

 according to another, group formation and adaptation (using 

 the term widely, Chapter IX) are due to different causes. 

 Whatever the truth may be, it seems quite certain that 

 adaptation itself appears to be established by the same sorts 

 of changes that lead to the divergences of races and species. 

 It may be, as we have suggested, that adaptive modification 

 is established far more by correlated changes than we are 

 aware of; but we have no right to assume this, and no 

 evidence at least to suggest that this is general. 



Now there is every reason to believe that the major groups 

 of the animal kingdom are originated by divergences of the 

 order of races and species — that they are, in short, the summa- 

 tion of such divergences. As a consequence, therefore, we are 

 led to look on the whole process of evolution, at least as regards 

 the stages by which it proceeds, as a unitary one. But as 

 the taxonomic divergences become more emphasised, they 

 become increasingly concerned with adaptive and functional 

 modifications, so that, if we are right in assuming that the 

 whole process is unitary, it seems that all divergences should 

 be adaptive ab initio. The unitary nature of the process tends, 



1 Various authors (notably Cope and Wigand, see Philiptschenko, 1927, 

 p. 91) have expressed strong doubts as to whether the higher systematic groups 

 have arisen by the progressive modification of lower ones. 



2 B 



