60 BASIS OF THE PEOBLEM 



fcion of plant life. Unless the occupied area is of very small 

 extent, there will be no difference except within this narrow 

 fringe. In the fringe there will be a lessening of elimination, 

 other things being equal, because there will not be the same 

 number of seeds which fail to grow into plants owing to the 

 previous occupation of suitable soil, as in the more central parts 

 of the area. When the new area has been entirely occupied, the 

 same conditions as existed in the smaller area will exist throughout 

 the larger area. Further, if the surface available for occupation 

 were indefinite in extent, there would, except at the fringe, which 

 would in this case be permanent, be no difference as regards the 

 amount of elimination. All that has been said applies equally 

 well if, instead of imagining these additions to take place after 

 evolution had reached its present stage, we imagine evolution 

 to have taken place from the beginning on an area of indefinite 

 extent. 



16. We have, therefore, some idea of the manner in which the 

 young of animals and plants perish. Let us consider any animal 

 species ; we find that the young are faced with a large number 

 of dangers. The new members of the species may be consumed 

 by some enemy before they have developed beyond the stage of 

 the fertihzed egg or at any stage in their development. They 

 may in general not meet with favourable organic and inorganic 

 surroundings, or at some particular stage they may not meet 

 with the environment necessary. At any time they may perish 

 from unfavourable external circumstances. The position of young 

 plants is similar, and in addition they may fail to find sufficient 

 space in which to live. 



The dangers which any species encounters remain both in kind 

 and in degree fairly constant over a considerable period of time, 

 and, unless in each generation a number of young survives at least 

 equal to the number of adults in the generation to which it owes 

 its birth, the species will dechne. It follows that the power of 

 reproduction must be such as to ensure that at least this number 

 of young will survive. The power of reproduction in any species 

 is therefore connected with the sum of all the dangers which the 

 young of the species encounter. But it is not true that the greater 

 the fecundity the better for the species. Eeproduction over and 

 above this degree would place the young in a less favourable 

 position. Competition bringing no corresponding advantages 



