THE RISE OF THE MAMMALIA 109 



mental powers ; the articulation of the upper and 

 lower jaws has shifted from the quadrate and 

 articular bones to the squamosal and dentary. But 

 in the Mammals, the characteristics which are of 

 the greatest interest and will principally engage our 

 attention, concern their method of reproduction and 

 of nourishing their young. It is a significant fact 

 that in the three great groups of animals in which 

 mental and social development have reached their 

 highest pitch, namely, Insects, Birds and Mammals, 

 we find that the care and nurture of the young are 

 carried to a high degree of perfection, and occupy 

 a very large share of the parents' activities. This 

 parental care for the offspring forms the basis, first 

 for family life and then for the formation and sus- 

 tenance of larger and more complicated societies, 

 and the social habits so engendered encourage the 

 development of the higher mental faculties, which 

 we seldom if ever meet with among the lower and 

 more individualistic creatures which take no further 

 interest in their eggs after they have been laid and 

 for whom parentage implies no ulterior duties. We 

 are therefore justified in paying special attention to 

 the peculiar modes of reproduction and nurture in 

 the Mammalia, as without their attainment social 

 man could hardly have been produced, and with 

 their decay, permanence or change the ultimate fate 

 of man is intimately bound up. 



