POPULAR SCIENCE 8t 



4. Our next example of a special human function is that 

 of the growth and metabohsm of the body. In 1908 Rubner 

 showed that man differs in a remarkable way from all the 

 other animals with which he experimented — horses, cattle, 

 sheep, pigs, dogs, cats, rabbits, and guinea-pigs. He arrived 

 at the following three conclusions : {a) During the early period 

 of growth of an animal the total amount of energy supphed 

 by the food is the same per unit of body-weight for all animals 

 except man. Each kilogram of weight requires for its pro- 

 duction food-energy equal to 4,800 calories. Man requires six 

 times as much, or 29,000 calories per kilogram. These results 

 are independent of the time taken to double the body-weight. 

 (b) In all these mammals the same fractional part of the total 

 food-energy, namely 34 per cent., is utihsed for purposes of 

 "growth. But in man this fraction is found to be on the average 

 only 5 per cent.- (c) The energy-value of the food consumed 

 per kilogram of body-weight during the period of maturity and 

 old age averages 191,000 calories for all the other animals, and 

 72 5 ,000 calories in the case of man. His age-limit was calculated 

 as eighty years. That is, man requires more than four times 

 the average of these animals per unit of body-weight. 



So far as I know, experiments have not been carried out 

 with any of the monkeys to see if they form a series leading 

 up to the singular position assigned to man. But in any case 

 it would appear that the unique brain and other distinctive 

 characters of man have not been achieved by exactly the same 

 forces as those of all the other mammalia. In all other animals 

 evolution appears to have run a uniform course and to have 

 brought forth uniform results, but man's metabolism appears 

 to be a special case. 



When did the Man-ape Stock Separate ? 



The current theory as to the later separation of the human 

 stock from the large ground apes is untenable for the following 

 reasons. A large animal — large for its own order, as the chim- 

 panzee among the primates — has always become specialised ; 

 special organs imply corresponding instincts, for instinct and 

 organ go together. It is always assumed that disuse can lead 

 to reduction in size, but as we shall see, it is very questionable 

 if a useless organ ever atrophies and disappears unless it is a 

 handicap to the survival of the animal. And if the animal 

 has acquired the organ and the mechanism and instinct to use 

 it, how can he reverse the experience of milHons of years and 

 take to a new experiment ? For example, the baboons have 

 efficient canine teeth and know how to use them against the 

 dogs of the hunters. They also occasionally make use of sticks 

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