NATURAL SELECTION 107 



Probably the rate of progress has varied much at different Varying 



rate of 

 progress 



periods. Any change of condition, climatic or other, must have ra 



necessitated adaptation. Emergence from the water to the land 

 led to the development of lungs, and the consequent better 

 oxidising of the blood was accompanied by the perfecting of the 

 heart. At the same time appeared the feathers of birds, the 

 hair of mammals, so that the heat generated in the body might 

 not be lost by radiation. One variation trod on the heels of 

 another, the stimulus occasionally coming from changed physical 

 conditions, more often from competing species. It is difficult to 

 stand still in a world of progress. When the butterfly became 

 more protectively coloured, the bird had to improve his eyesight. 

 If one species of vulture increased its range of vision, others 

 must follow suit, or arrive too late at the feast. If bees improved 

 their sight and means of extracting honey, other insects must 

 sharpen their senses, and improve their machinery, or else go 

 hungry. The lion and other beasts of prey increased the speed 

 of the antelopes by catching and eating the slow ones. They 

 themselves too then had to improve in speed or be left panting 

 in vain pursuit. On the other hand it would have been fatal for 

 them to improve over fast, for they would have destroyed the 

 species that supplied their larder, as the Maoris are said to have 

 exterminated the Moa, and as civilised man seems determined to 

 exterminate the African elephant and many of the noblest 

 mammals. 



But has this always been going on ? Are there not times Times of 

 when an equilibrium among species is attained, when each J^ ' 

 remains at its level and leaves others with which it comes in 

 contact undisturbed at theirs ? Are we not passing through such 

 a period now ? It is very difficult to answer such questions. 

 It is so recently that man began to observe accurately and record 

 his observations. Only forty years have passed since the publica- 

 tion of the Origin of Species gave purpose and system to the work 

 of naturalists. Allowing for all this, I think we may yet con- 

 clude that the present is not a time of rapid change among wild 

 animals. The progress in our domesticated species is a standard 

 of comparison, and it is impossible to deny that at times progress 



