i6 ESSAYS OF A BIOLOGIST 



cause is supernatural, outside the province of science, 

 that it is the expression of some eternal Idea, or some 

 plan of a personal creator (in which case, be it noted, 

 the idea or the plan often appears to our intellect as 

 unreasonable and indeed stupid) ; or finally that it 

 implies community of origin with later divergence 

 of development. When we are dealing with the 

 smaller subdivisions of some larger group, this method 

 too gives us information of the same order of accuracy 

 as does paleontology : but when we try to under- 

 stand the relationships of these larger groups, then we 

 are forced to renounce any claim to detailed knowledge. 

 In broad outline, however, a great deal still remains, 

 and this broad outline we can employ for our valuation 

 of the whole sweep of biological progress, just as we 

 can use the greater accuracy of vertebrate paleontology 

 and comparative morphology to fill in the detail 

 within a restricted field of its operation. From these 

 various evidences, direct and indirect, we can paint 

 for ourselves a picture of the evolution of life which, 

 in spite of inevitable gaps and errors, is in its main 

 features adequate and true. 



Let us not be misled by the fact that disputes can 

 and justifiably do arise over details : as Professor 

 Bateson put it recently ^ : — 



' If the broad lines do not hold, then we must sink 

 into irrationality or turn to flagrant supernaturalism.' 



Let us then remind ourselves of some of these 



broad lines. 



1 Bateson, '22. 



