The Hypothesis of Indiscriminate Mutability. 201 



B. Scott, one of the most prominent champions of the 

 theory of mutation, who, however, has declared against 

 the hypothesis of indiscriminate mutability on paleonto- 

 logical grounds. For it seems to me that this hypothesis 

 agrees perfectly well with the facts of paleontology and 

 especially with those wonderful genealogical series which 

 have lately been discovered. Unfavorable species may 

 well have arisen in far greater numbers than we should 

 ever imagine, without having left the shghtest trace in 

 geological strata. The continuous series certainly point 

 to selection in a constant direction during long periods 

 of time, but by no means do they in my opinion demand 

 a theory of mutability in a definite direction ; for their 

 explanation. 



A closer examination of Scott's arguments will show 

 how far my view is justified. Scott asserts that those 

 paleontological series which are well knowni, are con- 

 tinuous and without gaps ; whereas those in which the 

 gaps are many are just those which are imperfectly 

 known. This incompleteness is due either to the absence 

 of individual strata from certain periods or to the fact 

 that it has not yet been possible to examine the strata 

 in question, properly. But where the series of strata is 

 continuous and without gaps, and their examination thor- 

 ough, the genealogical tree has also proved to be contin- 

 uous and without gaps. This is evident in the case of 

 the well-known pedigree of the horse, in those of many 

 other mammals, of Ammonites and so forth. 



Such series always possess this remarkable feature : 

 they proceed, so to speak, in a straight line. Evolution 

 makes straight for its goal without deviation, swerving 



