i MIND AS A FACTOR IN EVOLUTION 3 



a branch there is little or no chance of returning to the 

 main stem, and for such a species further development 

 means movement further away from the line of ascent. 

 Look at any general scheme of organic evolution (Haeckel's, 

 for example), and consider the lines of divergence. 1 We 

 find, for example, Echinodermata, Arthropods, or Mollusca, 

 ranked as co-ordinate with the Tunicata from which Verte- 

 brates are derived. They are not stages in the evolution 

 of Vertebrates, nor can their further evolution bring them 

 nearer to the Vertebrate type. The crab does not become 

 more perfect by approximating insensibly to the Verte- 

 brates, but rather, if the expression be allowed, by becoming 

 more decisively and perfectly a crab that is, by develop- 

 ing those features, strength of grip, hardness of outer shell, 

 or whatever they may be, which distinguish it from other 

 Crustacea. The evolution of the dog, under the guidance 

 of man, has not made him more human, but has brought 

 out all sorts of canine qualities scent, strength, swiftness, 

 and the rest and carried each to perfection after its own 

 kind. Normally, evolution accentuates the existing ten- 

 dency, whatever it be. By whatever organ or faculty a 

 species is struggling to maintain itself, that organ or 

 faculty will be brought by the survival of the fittest to 

 the finest point of perfection. 



3. This perfection may, from any point of view but 

 that of success in the struggle for existence, be nothing 

 but degradation. Eyes become atrophied as a useless en- 

 cumbrance to animals that dwell in caves. A general 

 degradation of type is suitable to the parasite, and the 

 thick-skinned man gets on best in the world. There are 

 many instances of sheer deterioration in organic as in social 

 evolution, and in each case the lower type is that which 

 most successfully adapts itself to circumstances and manages 

 to survive. Nor, though the higher type may become 

 in some degree dominant, is the lower eliminated. The 

 primitive organic forms appear to have subsisted with 

 comparatively little alteration to the present day. At any 

 rate, no organism could be very much simpler than the 



1 Some good diagrams illustrating this point are given by Mr. Herbert 

 Spencer, Principles of Biology, Vol. I. Ch. XI. p. 388. 



B 2 



