LIMITS OF NATURAL SELECTION. 13 



occurred, so that evolution has been slow, and a 

 great number of individuals have progressed together, 

 kept abreast of each other by crossing. Marvellous 

 adaptations have been developed, but they were not 

 caused by natural selection. Natural selection, like 

 the stone walls of a labyrinth of lanes and avenues, 

 shows limits over which evolution cannot go ; but 

 as to why evolution should sweep through all the 

 intricate paths open to its progress, and how it 

 effects this progress, natural selection offers no clue. 

 Natural selection is a barrier to progress in certain 

 directions, not a cause producing progress. The 

 cause of this progressive development we must seek 

 in the properties of living matter and in the forces 

 which act upon it. For instance, the properties of 

 living matter which are displayed in the phenomena 

 of heredity must surely affect in some way the 

 progressive development of organisms. 



The present theories of organic development are 

 based chiefly upon evidence drawn from the corporeal 

 structure of plants and animals. Their anatomy 

 and the minute structure of their parts have been 

 analysed, compared, and classified, and in this man- 

 ner their genetic relationship has been made appar- 

 ent. While this method is sufficient to show their 

 relationship, and while observations of breeding and 

 artificial and natural selection show that there is an 



