3 1 4 THE POPULAR SCIENCE MONTHLY. 



creased depth of life we recognize only (but we recognize it clearly) 

 in the most advanced races of that animal which not only thinks and 

 reasons but reflects. 



We find, then, that the evolution of conduct is not only accom- 

 panied by increased fullness of life, but is to be estimated by such in- 

 crease. We do not say that that conduct is good in relation to the 

 individual which increases and that conduct bad which diminishes the 

 fullness of individual life in the individual. We assert, for the present, 

 only what observation shows that conduct of the former kind is 

 favored (other things equal), and therefore developed, in the life- 

 struggle, while conduct of the latter sort tends to disappear as evolu- 

 tion proceeds. 



Thus far we have only considered conduct in relation to individual 

 life. We have still to consider the evolution of conduct as related to 

 the life of the species. 



In considering the evolution of structures and functions we have 

 not only to consider the influence of the struggle for inidvidual exist- 

 ence, but also the effects of the contest in which each race as a whole 

 is engaged and to do this we have to consider, first, those circum- 

 stances which affect the propagation of the race ; secondly, the relation 

 of the individuals of the race to their fellows ; thirdly, the relations of 

 the race as a whole to other races. Something akin to this must be 

 done in considering the evolution of conduct. We have seen how 

 modes of conduct which favor the continued existence of the individu- 

 al are developed at the expense of modes of conduct having an oppo- 

 site tendency. These last die out, because the individuals of the race 

 who act in these ways die out. But it is obvious that conduct will be 

 equally apt to die out which tends to prevent or limit the adequate 

 renewal of the race from generation to generation. It is equally ob- 

 vious that whatever conduct causes contests (whether for life or sub- 

 sistence) within the race or species, tends to the elimination of mem- 

 bers of the race, and so diminishes the chances of the race in the 

 struggle for existence with other races. Lastly, the relations of a race 

 to surrounding races are manifestly of importance in the evolution of 

 conduct, seeing that conduct will equally tend to be diminished 

 whether it is unfavorable to the existence of the race in which it is 

 prevalent, or simply unfavorable to the separate existence of an indi- 

 vidual member of the race. 



Now, with regard to conduct affecting the propagation of a race, 

 we find that, like conduct affecting individual life, it has been devel- 

 oped from what can hardly be called conduct at all in the lowest 

 grades of life to fully developed conduct, with elaborate adaptation of 

 means to ends in the highest. In the lowest forms of life, propagation 

 proceeds by mere division and subdivision, not depending so far as can 

 be judged on any power of controlling the process, which such creat- 

 ures may possess. In fact, the Protozoa multiply by dividing. We 



