DARWIN'S NATURAL SELECTION 49 



His famous theory may be formulated under 

 the three following heads : 

 (i) Heredity. 



(2) Variation. 



(3) The struggle for existence, with its 

 resultant, survival of the fittest. 



Darwin requires very little of heredity, and 

 what he does ask is beyond dispute. It is 

 enough for his theory if like begets like and 

 ''figs do not grow on thistles.'' 



Similarly with variation, the demands of his 

 hypothesis are very slight. If it be conceded 

 that variation is a fact, that offspring do vary 

 from their parents and each other, it is 

 enough. And who will dispute this in a world 

 where no two creatures are exactly and in all 

 particulars alike? The apparent contradiction 

 that, heredity demands likeness, while varia- 

 tion requires difference, is confined to the sur- 

 face — it is not real. The likeness is general 

 while the difference is particular. A sheep may 

 be born with shorter or longer legs, by varia- 

 tion; but it will be a sheep and not a horse, 

 by heredity. 



As an example of the working of the theory 

 let us take Lamarck's piece de resistance, the 

 giraffe. Lamarck says: "We know that this 

 animal, the tallest of mammals, inhabits the 

 interior of Africa, and that it lives in localities 



