THE PRINCIPLE OF CO-OPERATION 361 



animals developed, in addition to the general automatic co-opera- 

 tion inherent in living matter, a new toleration for close aggregation 

 in a limited area, where they had collected not as a result of a social 

 appetite but on account of their individual reactions to the sur- 

 rounding environmental conditions. Such collections occur fre- 

 quently as the result of forced movements in which the animal re- 

 acts, apparently mechanically, to the forces operating upon it, and 

 may persist only because of the inertia of toleration. These tropisti- 

 cally conditioned groupings show survival values in addition to those 

 resulting from the general co-operation of which we have spoken so 

 frequently. Such additional survival values may be shown either by 

 the effect of the group upon the individuals, rendering them more 

 /esistant to adverse environmental conditions, or conversely by so 

 effecting the environment by the removal of toxic materials, or by 

 some other ameliorating device, that it becomes more favorable for 

 the continued existence of th-e animals. Group survival values can 

 slip into the background as animals become well adjusted to the 

 environment, to reappear apparently afresh when conditions of exist- 

 ence become again less favorable. These new survival values may 

 be qualitatively as well as quantitatively different from those shown 

 previously. 



(^ The last advance in this series comes when individuals cease to 

 react as separate units and respond only as members of a group — 

 when, as in the case of ants or termites and, rarely, with men, they 

 are largely group-centered rather than self-centered^ Many of the 

 so-called "altruistic" drives in man apparently are the development 

 of these innate tendencies toward co-operation, which find their 

 early physiological expression in many simpler animals. 



With the development of the nervous system, closer co-operation 

 becomes possible and larger numbers are affected. There is much 

 reason for thinking that many of the advances in evolution have 

 come about through the selection of co-operating groups rather than 

 through the selection of individuals. This implies that the two great 

 natural principles of struggle for existence and of co-operation are 

 not wholly in opposition, but that each may have reacted upon the 

 other in determining the trend of animal evolution."^ 



