Endless Variation J 45 



No Two Alike 



As one travels about and sees farmyards and the back- 

 yards of various homes he can recognize domestic animals 

 as pigs and chickens, cows and horses, sheep and geese. In 

 spite of the differences between the cows on one farm and 

 those on the next, we think of them all as of the same species. 

 We are not astonished by the great variations in the scrub 

 animals or by the great variations that we see at a dog show 

 or at a county fair. We feel that it is of the nature of ** dog " 

 to be all the different-looking beings that we see. In some 

 regions or on some farms we may observe a considerable 

 uniformity among the cows. Again we are not astonished 

 at the uniformity of these animals. We ascribe this uni- 

 formity to better breeding, or to careful selection of stock, 

 without inquiring too closely into the methods by which it 

 has been brought about, or into the meaning of the process. 

 We feel that it is in the nature of white Leghorns or of polled 

 Herefords to be fairly uniform. We see many different 

 kinds of apples or plums or grapes, and we take the variety, 

 as a matter of course. And when we see the uniformity of a 

 particular lot of apples or grapes we again take this as a 

 matter of course. 



The persistence of characters which is recognized in 

 our concept of heredity combines with the equally persistent 

 variability of living things to produce a moving equilibrium. 

 This is from one point of view the life of the individual, and 

 from another point of view it is the evolution of species. In 

 the case of the individual, preservation of identity during 

 constant change involves an effective adjustment to the sur- 

 roundings. In the case of a species or a race there is genetic 

 or germinal continuity and change in the course of time, 

 with adaptation at every point to the conditions of existence. 



This presentation of the life of the individual and the 

 life of a race is not a mere metaphor. Our very concept of 

 species involves fitness just as does our concept of life in the 

 individual. We are concerned with distinct groups of ani- 

 mals that are capable of living and of maintaining them- 



