366 The Outline of Science 



The Factors in Evolution 



But "Darwinism" is more properly used, in a stricter sense, 

 to mean Darwin's theory of the factors in evolution. If birds 

 sprang from Dinosaur reptiles, if the modern horse is the descend- 

 ant of Eohippus, which was about the size of a fox-terrier, how 

 did the gradual transformation come about? There were many 

 evolutionists before Darwin, and some of them propounded 

 theories as to the factors in the age-long process. But Charles 

 Darwin and his magnanimous fellow-worker, Alfred Russel 

 Wallace, thought out a coherent theory of the factors a theory 

 that fitted the facts so reasonably well that it soon won the con- 

 viction of a large body of naturalists. The essence of the Dar- 

 winian theory is in the two words Variation and Selection; and 

 Darwin stated it in a couple of sentences: "As many more indi- 

 viduals of each species are born than can possibly survive, and as, 

 consequently, there is a frequently recurring struggle for exist- 

 ence, it follows that any being, if it vary however slightly in any 

 manner profitable to itself, under the complex and sometimes 

 varying conditions of life, will have a better chance of surviving, 

 and thus be naturally selected. From the strong principle of 

 inheritance any selected variety will tend to propagate its new and 

 modified form." 



The Essence of Darwinism 



This is, however, too terse a statement. It requires some dis- 

 entangling and expansion. Proposition I. Variability is a fact 

 of life. Offspring are usually somewhat different from their 

 parents and from the other members of the family. Some of these 

 variations make for success success in getting food, in avoiding 

 enemies, in securing mates, in giving the next generation a good 

 start, and in other ways. Individuals that have varied in a profit- 

 able way will succeed better than those that have varied in the 

 opposite direction, and better than those that have not varied 

 at all. 



