IN THE GRIP OF AN ICE AGE 55 



reptiles would have, at first, thin scaley coats of little 

 use. The amphibians had the clammy skins of our 

 frogs and newts. None of the animals had had 

 occasion to develop warm coats. None of them had 

 hearts so constructed as to keep the blood at an even 

 temperature. However, the climate changed. I have 

 walked on the brink of Niagara and by the lake side 

 at Chicago in just the same clothing as I wear in 

 the early summer in London, without any particular 

 discomfort. The mammal has a four-chambered 

 heart, and the blood is so well supplied with oxygen 

 to burn its "fuel" that it keeps warm. None of the 

 animals before the Permian Revolution had "warm 

 blood." There had been no need of it, and needless 

 things are not evolved. If some theories of evolution 

 were true, they might be. On the lines of natural 

 selection they are not. 



But on the theory of natural selection they are 

 evolved when they are needed, and this is the positive 

 or constructive side of the matter. We have seen 

 that the three great new requirements in the higher 

 animals were care of the eggs or young, a four- 

 chambered heart, and a warm coat. You probably 

 know that these are the chief points in which the 

 mammals and birds are superior to the reptiles. You 

 will understand half of familiar nature better in future 

 if you remember that these superior qualities were 

 made necessary by a great Ice Age, nine or ten million 

 years ago, and were evolved in the latter part of the 



