196 The Science of Life. 



tion, that the struggle is most severe between closely- 

 allied forms should not be more carefully substantiated 

 than it usually is. Darwin gave some half-dozen 

 examples, not all of which are correct. The necessity 

 for the struggle depends upon: (a) the tendency of 

 organisms to rapid increase; (b) the variability of the 

 physical environment, to which organisms are at best 

 only relatively well adapted; and (c) the secondary 

 consequences of these primary facts; but it is the un- 

 fulfilled duty of the student of bionomics to accumulate 

 a mass of precise evidence. 



It is plain that the nature of the struggle must vary 

 greatly with the nature of the organism; thus that of 

 the beech-tree must be very different from that of the 

 squirrel. It is plain that the phrase includes at least 

 three different forms of struggle : with related fellows, 

 with foes, and with inanimate nature. The objects of 

 competition include (i) continued individual existence 

 and well-being, and (2) the continuance of family and 

 kin both of them objects of great complexity. It is 

 also a familiar fact that the struggle varies in intensity 

 with the rate of reproduction and with the variability of 

 the environment. Thus we reach the conclusion that 

 the struggle for existence is a function of numerous 

 partly dependent, partly independent variables. 



Taken literally, the "struggle for existence" seems 

 somewhat too strong a phrase to use in describing the 

 pursuit of such luxuries as a seventh wife, or that con- 

 tinuous endeavour after well-being which ensures a few 

 years longer life to the stronger constitution. But even 

 when the phrase is literally appropriate, we must re- 

 member the altruistic colouring of many facts of life 

 attraction between mates, reproductive sacrifice, paren- 

 tal and filial affection, the kindliness of kindred, gre- 

 gariousness and sociality, co-operation and mutual aid. 



Observation shows us what we are tempted to call 

 mere physical attraction between cells which are at the 

 same time entire organisms. In some types of simple 

 many-celled animals, and in most plants, the attraction 

 remains cellular, being confined to the sex-cells. Gradu- 

 ally there appears, as we ascend the animal series, a 



