35 



hardly be appreciated by one who has not given attention to the matter. 

 To a casual observer, it may appear as if the most worthless individuals 

 got a living, while the better perished. The well-favored do often suc- 

 cumb, and in ordinary times the weak may escape ; but when periods of 

 great food-scan^ity, or of intense heat or cold, or of drought come, then 

 the weak perish miserably. The eggs produced by some fishes reach into 

 the millions. Could each one develop into an adult fish, which should 

 in its turn give origin to an equal number of off'spring, a very few years 

 would sufiice to fill all the seas with that fish. As it is, only perhaps one 

 egg in a million becomes an adult fish. The least protected eggs are 

 swallowed by enemies, the weakest young fishes die from disease and ex- 

 posure, while only the most vigorous escape. 



Our wild rabbits pro'luce several young at a litter and a number of lit- 

 ters each year; yet the number of rabbits does not, on an average, in- 

 crease. As many rabbits must therefore die each year as are born, and 

 they seldom die of old age. Dogs and men, extreme cold and hunger, 

 carry them ott' by thousands. Is there not here abundant opportunity 

 for the development of swiftness of foot, acuteness of eye and ear, and of 

 endurance ? 



As long as the environment remains about the same, little or no change 

 may occur in the structure or specific characters of animals ; but the 

 whole organization is kept up to the highest grade of efficiency. Should 

 there, however, be a gradual change in the conditions under which any 

 animal is living, there would come about a corresponding change in the 

 animal itself. Should there, for example, be developed a gradual increase 

 in the speed of our dogs, there would, I doubt not, occur a corresponding- 

 improvement in the swiftness of our rabbits. I can see no reason for 

 supposing that natural selection would not have the same effect here as 

 man's selection does in the case of trotting horses. 



Darwin's theory of natural selection was based almost entirely on ob- 

 servations made on domesticated animals and plants. Organisms in a 

 state of nature did not seem to him to be subject to such frequent and 

 extensive variations, ^^e are only now beginning to appreciate how 

 numerous and how important these variations are. They do not affect in 

 only a slight degree a single organ of one individual in a decade or a 

 century, but isrobably every organ of every individual, and to a veiy 

 appreciable extent. The proverbial unlikeness of the individuals of every 

 species is due to this variation. Wallace, in his "Darwinism '' has given 



