THE DARWINIAN THEORY 43 



urticce), or all the chaffinches. If the individuals are earefially com- 

 pared it will be recognized that, even in these relatively constant 

 species, no. individual exactly resembles another; that even among 

 buttertlies twenty black scales may go to form a particular spot on 

 the wings in one individual and thirty or twenty-five in others ; that 

 the length of the body, the legs, the antennae, the proboscis exhibit 

 minute differences ; and it is probable that the same combination of 

 quite similar parts never occurs twice. In many animals this cannot, 

 of course, be proved, because our power of diagnosis is not fine 

 enough to be able to estimate the differences directly, and because 

 a comparison of measurements of all the parts in detail is not practic- 

 able. So we may here confine ourselves to the differences in the 

 human race, which we can recognize with ease and certainty. Even 

 as regards the face alone, all men differ from one another, and, 

 numerous and complete as likenesses may be, it is impossible to find 

 two human beings in which even the characters of the face are 

 exactly similar. Even so-called ' identical twins ' can always be 

 distinguished if they are directly compared either in person or in 

 a photograph, and if the rest of the body be also taken into con- 

 sideration we find numerous small, sometimes even measurable 

 differences. 



The same is true of animals, and it is only our lack of practice 

 that is at fault if we frequently fail to detect their individual 

 differences. The Bohemian shepherds are said to know personally, 

 and be able to distinguish from all the rest, every sheep in their herds 

 of many thousands. Thus the factors of variability and transmissi- 

 bihty must be granted, and it remains only to ask : Who plays the 

 part of selecting breeder in wild nature? The answer to this question 

 forms the kernel to the whole Darwinian theory, which ascribes this 

 role to the conditions of life, to definite relations of individuals to the 

 external influences which they meet with during the course of their 

 lives, and which together make up their ' struggle for existence.' 

 To make this idea clear I must to some extent diverge. 

 It is a generally observed fact that, in every species of animals 

 or of plants, more germs and more individuals are produced than 

 grow to maturity, or become capable of reproduction. Numerous 

 young individuals perish at an early stage, often because of unfavour- 

 able circumstances— cold, drought, damp, or through hunger, or at the 

 hands of their enemies. When we ask which of the progeny perish 

 early, and which survive to carry on the species, we are at first sight 

 inclined to suppose that this is entirely a matter of chance ; but this 

 is just what Darwin disputed. It is not chance alone, it is, above all, 



