70 



THE AMERICAN NATURALIST 



[Vol. XLVII 



is about the least adaptable beast we know. The Cepha- 

 lopods with complex partitions have all perished. The 

 bizarre Trilobites similarly persisted each for but a brief 

 period. 



I would not claim that the over-ornamentation in these 

 cases was the cause of extermination. It seems more 

 probable that it is merely one noticeable indication of a 

 general unbalanced condition of the organism, a condition 

 affecting probably function as well as structure. I sus- 

 pect that more species have perished because of physio- 

 logical maladjustment than from any disadvantageous 

 structural qualities. 



In quatenary times in numerous species, great empha- 

 sis seems to have been laid upon bulk and the very huge- 

 ness of some of these species probably aided in their ex- 

 termination. 



Non-adaptive qualities, when first appearing, may 

 often be comparatively harmless, at least may not be 

 sufficiently hurtful to lead to the extermination of the 

 species in which they appear. But qualities compara- 

 tively innocent in their beginnings, when over-empha- 

 sized by such trends as we are discussing, may go beyond 

 the limit that even long suffering nature will allow and 

 extermination follow. The goblin of natural selection 

 will get him in the end if he doesn't watch out. It is a 

 case of giving the species rope enough and letting it hang 

 itself. Instead, therefore, of supplanting natural selec- 

 tion, such orthogenesis as this really acts in the end to 

 aid in eliminating many species whose characters in their 

 beginnings were indifferent, natural selection finally dom- 

 inating and compelling adaptation. 



Since mutation-trends in helpful directions will be 

 aided by selection, through the destruction of the rivals 

 of their possessors, while hurtful trends will cause ex- 

 tcrjnmation, we see that natural selection has a determi- 

 native influence upon the direction of evolution, steering 

 the species along safe paths of progress. 



Further advance in the study of the method of evolu- 

 tion may be expected from the study of trends in muta- 

 tion. Such study should be continued for many years, 



