438 V. THE NATURE OF EVOLUTION 



numerous its youngs, a consequence which must be most purposeful 

 for the survival of small animals, since numerous victims may always 

 be demanded by their enemies. This may likewise contribute greatly 

 to the natural selection of the fittest, so that the character will 

 become more and more fitted for survival. The reverse may be true 

 when the animal increases in its size, there being no room for the 

 natural selection on account of its poor procreative power, and also in 

 this respect there is a strong reason for the extinction of large-sized 

 animals. 



Since there may be no natural selection in such animals, their 

 evolution should be orthogenetic and animals bound to be extinct by 

 their overspecialization are always to advance on an orthogenetic 

 course. It appears, however, that Nature has prepared an excellent 

 mechanism to check this terrible orthogenesis. The mechanism may 

 be based upon the want of food, which is expected to occur when 

 animals greatly increase their size. Inanition may not only inhibit 

 the active function of hypophysis, but may stimulate thyroid or related 

 glands to make the evolutionary course entirely reverse. Reptilians 

 might accomplish the orthogenesis until they became extinct presumably 

 because there were too plentiful food to make them hungry. 



Orthogenetic, unlimited increase in size, therefore, may occur 

 rather rarely. In general, an animal having increased in its size to a 

 certain extent may cease to become bigger through the want of food, 

 as the bigger an animal, the food may be required the more. On the 

 contrary, an animal having become smaller and smaller may sometimes 

 begin to increase in size owing to the sufficiency of food-supply be- 

 cause small animals need only a small quantity of food. In this way, 

 the quantity of food may always control the size, accordingly, the 

 specialization rate of animals. 



HoAvever, civilized man is able to escape this want of food, however 

 big he becomes, owing to the high civilization, and therefore, for the 

 future, the character difference between civilized and uncivilized man 

 will become amazingly great, and when the overspecialized, civilized 

 man is extinct, the latter will represent the mankind, but those who 

 escape the extinction will follow the fate of the former after migrating 

 into the stimulating climate. 



When one surveys the entire field of animal evolution, the 

 significant fact becomes apparent, not only from the geological but 

 from the facts of comparative anatomy, that each great distinctive 

 new group in animals has always sprung from the more primitive 

 member of the preceding group, [not from those highly specialized. 

 Mankind may not provide an exception. 



The extinct Cro-Magnon people are known to have a stately stature 



