7.6 BASIS OF THE PEOBLEM 



in succeeding years remains much the same. The instances of 

 a marked increase in the number of any species are rare, and are 

 usually traceable to the intervention of man, as the result of 

 which certain of the dangers which normally confront the young 

 have been removed. It follows, therefore, that normally of the 

 many thousands of fertilized eggs of a fish, for example, all but 

 two perish. Even when the most rapid increase ever observed 

 is taking place, the great majority of young perish. From a con- 

 sideration of the circumstances it is evident that upon the whole 

 those individuals which present certain characters will have 

 a better chance of surviving than others which do not present 

 these characters. 



This point demands further consideration, because upon it 

 turns the whole question of natural selection. What is involved 

 in this theory is that the death-rate is selective, that those in- 

 dividuals which are best adapted to the surroundings which 

 confront the species do, on the whole, have a better chance of 

 survival. It is adaptation which determines fitness, but the 

 concept of adaptation does not of necessity include any idea of 

 progress. Given any complex of surroundings such as that which 

 confronts any species, there may be a more or less close fitting 

 of the organisms to this complex. The closeness of this fitting 

 may have been obtained by a simplification of structure, a com- 

 plication of structure, or it may be that for long ages the close- 

 ness of the fitting has been attained by the elimination of depar- 

 tures from the mean of the species in any direction and the 

 preservation of the average type. 



In this connexion it has often been pointed out that the death- 

 rate in certain cases is not selective, and does not therefore involve 

 the survival of the more fit and the elimination of the less fit. 

 When the whale opens its mouth and engulfs vast numbers of 

 small organisms upon which it feeds, there is apparently no 

 escaping of certain types of these organisms accompanied by 

 a greater elimination of other types. But these cases are not on 

 the whole common, and further there is nothing in such oases 

 which counteracts selection ; it merely means that sometimes 

 selection is not operative. A consideration of the mode of opera- 

 tion of the factors of elimination, the general nature of which has 

 been indicated, leads without any doubt to the conclusion that 

 in the vast majority of cases, when any organism meets its death, 





