120 Je LIONEL TA VEER [AUGUST 
the fact that the particular variation in question must have been too 
small to be by itself of selection value. In many cases the particular 
variation would, no doubt, if taken alone be, as the objector asserts, 
too unimportant to be selected, but as it is the whole organism that is 
selected, it is not logical to make an artificial separation and study the 
development of one organ or structure irrespective of the other organs 
with which it is in nature associated. Lvery organ in its evolution 
must be considered in relation to the whole of the particular organism 
in which that particular stage of development of that organ is found. 
Starting therefore with this fact that the net value of adaptability of 
the whole organism to its environment must be the basis which deter- 
mines selection or elimination, it will follow that certain lines of 
development will result from the application of this criterion. In a 
series of organisms placed under new conditions, elimination will pro- 
ceed along lines essential to bring about a proper adjustment to the 
new conditions. If the offspring of these adjusted organisms merely 
repeated in their generation the characters of the exterminated as well 
as of the surviving organisms, that temporary adjustment would be 
permanent as long as the conditions were unchanged. But since the 
offspring are produced only by the surviving organisms, selection is 
continually raised to higher and higher planes of adaptation, and 
therefore, as long as conditions remain constant, the tendency of 
selection must be, as Darwin clearly saw, cumulative. He did not, 
however, apparently see that from this cumulative tendency definite 
variability must arise out of indefinite. 
Selection in direct relation to climatic conditions is therefore of 
very minor importance, while selection among the members of a 
species and all forms of inter-organismal selection is of infinitely more 
importance, since it is this interaction, produced by the offspring in 
different degrees inheriting the advantages of both parents (both of 
whom have survived on account of certain advantages), that leads to 
the cumulative development and never-ending struggle for survival. 
Darwin came very near to this conception of definite variability when 
he pointed out that “if a country were changing the altered conditions 
would tend to cause variation, not but what I believe most beings vary 
at all times enough for selection to act on.” Extermination would 
expose the remainder to “the mutual action of a different set of 
inhabitants, which I believe to be more important to the life of each 
being than mere climate,’ and as “the same spot will support more 
life if occupied by very diverse forms,’* it is evident that selection 
will favour very great diversity of structure. 
Bearing in mind this cumulative action of selection it will follow 
that under constant or relatively constant conditions the struggle for 
successful living will become more and more selective in character, 
1 From Poulton’s ‘‘ Charles Darwin and the Theory of Natural Selection” (Abstract of 
Darwin’s letter to Professor Asa Gray). 
