THE PURPOSE OF YOUTH 225 



the prodigality of Nature rather than to her inventiveness, is 

 gradually replaced by a new method. The number of the young 

 is very greatly reduced, and the small families are protected by 

 the parents. Sometimes the eggs are retained in the body of the 

 mother until they are nearly ready to hatch ; sometimes they 

 hatch within her body and are fed from her blood ; sometimes 

 even the eggshell is dispensed with, and from the earliest appearance 

 of the embryo as a separate speck of living matter, it is fed from 

 the blood of the mother. The eggs may be laid in places carefully 

 prepared by the mother or by both parents, and eggs and young 

 may be fed and guarded for long. The young, even if born in an 

 active condition, may be fed and protected by the parents for years 

 or months. Instead of hundreds of thousands of helpless young 

 dumped on a careless and hostile world, a very small number, 

 sometimes only a single individual, is produced at a time and cared 

 for in the most complete fashion. 



In the highest animals, and especially in mammals, the young 

 are freed from the trouble of finding their own food ; they have very 

 seldom to defend themselves, and the changes from egg to embryo 

 'and from embryo to adult are made as simple and direct as possible, 

 and none the less the duration of the period of youth increases as we 

 go up the scale of animal life. This lengthening of youth is specially 

 plain when we compare the different members of a single group. 

 If we take the human race and its allies, the apes, monkeys and 

 lemurs, then man, who is at the top of the scale, has the longest 

 youth, and even in the lower and less civilised races, it would be 

 'unsafe to assign less than fifteen years to immaturity, whilst in 

 the higher and more civilised types it is stiE longer. The great 

 apes, the gorilla, orang and chimpanzee, take from eight to twelve 

 years to grow up. The baboons and common monkeys take from 

 three to eight years, and the little South American monkeys and 

 kmurs require only two to three years. If we take weight or 

 stature of the body, the strength of the muscles or any of the purely 

 physical qualities, we shall find that they do not fit this varying 

 scale of youth. There is only one part of the body that can be 

 reconciled with it. 



In the figures (Fig. 36) I show the contour of the brain in a set 

 of primate animals drawn roughly to scale. It will be seen at 

 once that man, with the longest period of youth, has the largest 

 brain ; that although a chimpanzee may equal or exceed a man 

 in size and weight, its brain is much smaller ; and that the brain 



C.A. P 



