DURATION OF YOUTH IN MAMMALS 41 



importance than actual size. Within each group of nearly related 

 animals, the duration of youth is in rough agreement with the 

 possible span of the whole life, and with the relative size to which 

 the members of the particular species attain. But the agreement 

 is not exact. There are very many instances in the animal 

 kingdom, and I shall mention some of them, in which there is no 

 reasonable proportion between size or the potential longevity, and 

 the duration of youth. 



The descending scale from man to the lowest monkeys, which is 

 fairly plain in the case of size and of longevity, is quite certain if we 

 take into consideration the complete structure and especially the 

 mental capacities of the members of the series. When animals 

 belonging to different groups are compared, it is not very easy 

 I to say which is to be regarded as higher and which lower. Most 

 'persons would agree that the cats, including the large cats like the 

 Hon and the tiger and the small cats like the domestic cat, are the 

 highest of the carnivorous animals. But is a cat a higher or lower 

 animal than an elephant ? Inside a group, however, comparison is 

 easier, and especially if we take into consideration the size and 

 structure of the brain, there is no doubt but that man stands 

 supremely at the head of his tribe and that there is a rapid descent 

 from him to the lowest monkeys. The most certain and the most 

 important feature about the differences in the duration of youth, 

 and what is specially clear in the case of man and his relations, is 

 that the length of the period of youth varies with the degree of 

 intelligence to which the adult can attain. Civilised man is the 

 most intelligent and takes longest to grow up ; the smallest monkeys 

 are the least intelligent and hurry over the period of youth most 

 quickly. 



As a good many of the Carnivora have bred in captivity, we have 

 a fairly extensive knowledge of the duration of their youth, although 

 it is to be remembered that the new conditions to which they are 

 subjected may have an effect on their rates of growth, probably 

 accelerating it. Lions and tigers take only from three to five years 

 to become adult ; both sexes are capable of breeding, and the males 

 have got good manes soon after they are three years old, but they 

 may go on growing for several years after that. Leopards, lynxes 

 and caracals and the smaller cats generally, take from one and a half 

 to three years to become adult. A jaguar cub born in the London 

 Zoological Gardens was not nearly half grown when it was a year 

 old. Although it was brought up by its mother, it soon became 



