SICKNESS AND GROWTH 153 



porarily inhibited in children by even slight illnesses. 1 

 Periodic measurements of the circumference of children's 

 heads have shown that growth may be represented by a 

 curve with a regular sweep, which curve, however, shows 

 checks in the growth exactly corresponding to periods of 

 infantile illness. It is important to note that the arrest 

 "was not made up for by aftergrowths." There is every 

 reason to suppose that as the growth of the skull was 

 checked during these periods of illness, growth in the rest 

 of the body was checked also. In any case an inborn 

 character was modified. This must have been going on 

 ever since man appeared, for hardly any children escape 

 brief periods of illness. We do not find, however, that 

 there is any evidence that this constant and long-continued 

 acquirement has diminished the stature of man, for the 

 most ancient prehistoric remains show that the then existing 

 races were much the same in size as the races existing at 

 the present time. 



If the inheritance of acquired characters is usual, we 

 ought then to find improvement in races subject to the 

 most favourable conditions and degeneration in races sub- 

 jected to unfavourable conditions, for if an unfavourable 

 environment injures the individual from childhood, and 

 the germ cells are influenced by the action of the environ- 

 ment upon the individual, the unfavourable environment 

 must injure the germ cells. 



Observed facts seem to contradict this suggestion in the 

 strongest manner possible. In parasites which live inside 

 other animals, the conditions of living are extremely favour- 

 able. The parasite has its food supplied to it, and has no 

 enemies from which it is obliged to escape. It would be 

 difficult to imagine conditions more favourable to the well- 

 being of the individual. We find, however, that in parasites 

 the tendency to degenerate from the parent forms is universal. 

 While closely allied free living species have complicated 



1 Galton, Inquiries into Human Faculty, Everyman's Library Edition, pp. 

 168-69. 



