INFANCY AND PARENTAL CARE 



335 



for a long time after birth. Among the marsupials , or pouch 

 animals, like the kangaroo and the opossum (see Fig. 158), the 

 young are placed in an abdominal pouch immediately after 

 birth. In all the other mammals the young suckle from the 

 milk glands of the mother. As we go from the lower mam- 

 mals to the higher, we find that the infancy of the individual 

 becomes proportionately greater or longer. 



This is true even if we compare different races of mankind. 

 Among the primitive savages children are allowed to run about 

 without anyone to watch them as soon as they can walk ; in a 

 civilized community we sometimes keep close watch over chil- 

 dren, even at their play, for several years. It is easy to see 

 the advantages of a long youth from the point of view of more 

 and more complex civilization. There are physiological dif- 

 ferences also connected with the relative length of infancy. 

 This is shown, for example, by the length of time it takes the 

 individual to reach maturity. 



The table below shows the duration of the growing period 

 for a number of animals, including man. 



GROWING PERIOD OF VARIOUS MAMMALS 



