THE TRIUMPH OF THE MAMMALS 103 



modern horse with one toe and one toe-nail (hoof) 

 was born. 



We can in the same way trace the evolution of 

 most of the mammals. We have found the bones of 

 the ancestors of the elephant for many generations, 

 and can say how its trunk was developed. We find 

 its canine teeth growing steadily longer. Perhaps 

 they were used for digging succulent roots. The 

 nose, to be of any use, had to keep pace with the 

 teeth in length, and the chin grew out to the same 

 length to bear the weight of the nose. When nose, 

 teeth, and chin became about a foot long, the nose 

 (or trunk) developed powerful muscles attaching it to 

 the skull. The chin again retired — we trace all this 

 in fossil elephants — and the elephant was left with 

 two very long teeth and a very long nose. 



In much the same way, we can trace the evolution 

 of the camel, the bear, the seal, the dog, the cat, the 

 pig, and so on. We can follow the development of all 

 the bewildering varieties of teeth, of claws, of limbs, 

 of hairy coats, of horns, of eyes, of noses, of breasts, 

 etc. Food and safety are the keys to most of their 

 structures. Sexual selection — the choice of a mate 

 with certain features— explains other things: the 

 smooth face of some monkeys, the lion's mane, and 

 other features. Evolution is the great key. It puts 

 together the jig-saw puzzle of nature as no other 

 human thought ever did. 



"Struggle" is only part of the mechanism. We 



