CHAPTER IX 



THE TRIUMPH OF THE MAMMALS 



The birds are our "sisters" in a way that poets do 

 not know. We, the mammals, and they were born 

 together of the Permian Revolution. We are the 

 common offspring of an Ice Age. That is the original 

 reason why we are ''warm-blooded." And warm 

 blood also means better blood, better nourished 

 brains, so that it was a great advance in organization. 

 Surely these things make nature more intelligible 

 than it was even to the more learned of our fore- 

 fathers? But we will now consider more closely the 

 origin and spread of the vast mammal family to which 

 we belong. 



Mamma is the Latin word for breast. Our very 

 young children are not aware that they are speaking 

 a famous dead language when they address their 

 mothers by that word, but it is a fact that to the 

 Roman baby its mother was above all things a 

 mamma — a breast. The mammals are therefore the 

 animals with breasts; or, to take their leading differ- 

 ences from the other Vertebrates, with breasts, a 

 womb, a four-chambered heart, and a hairy coat. 

 You see at once that all these superiorities mean, first, 



92 



