MAN AND THE APES 161 



tion shows us that the continuous use of the joint has no 

 effect whatever in the way of wearing out the surfaces of the 

 bones in the absence of disease. 



Another difficulty with regard to the inheritance of 

 acquired characters is, that acquirements are not made in 

 the case of all characters. It is known that the nerve cells 

 do not multiply after birth, at any rate in the case of 

 mammals. The young individual is born with its full 

 complement of nerve cells, and the number is never in- 

 creased in after life. Now it is obvious that evolution in 

 the higher animals, culminating in man, has worked through 

 the increase of the intelligence particularly through the 

 increase of the nervous tissue of the brain in proportion to 

 the size of the animal. The differences between man and 

 the higher apes are most marked in the case of the brain. 

 Man's brain is very large in proportion to that of the highest 

 ape, and the surface area of the human brain that is, the 

 most important part of it is in proportion larger still. But 

 this means an increase in substance in the number of 

 nerve cells in the brain at any rate and we have no jot of 

 evidence to show that any acquirement of the individual 

 can add a single cell to the brain. On the contrary, we 

 know that if a nerve cell is destroyed by accident or disease, 

 it is gone for ever. It is never replaced by the multiplica- 

 tion of other similar cells as may happen in other tissues in 

 the body. Therefore the only acquirements that can be 

 made, in so far as the substance of the brain is concerned, 

 by man and the higher vertebrates, are losses. 



Many other characters that are inherited do not depend 

 upon use for their appearance, and yet have very obviously 

 appeared or been increased in the later stages of evolution. 1 

 These cannot be dependent upon the transmission of the 

 acquirements of the parent to its offspring, for they are 

 not modified by use or disuse on the part of the organism in 

 which they occur. If, then, the transmission of acquired 

 characters has played an important part in evolution, there 



1 Such characters are the plumage of the peacock and cock pheasant. 



