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 accompanied by increased fullness of life, but is to be estimated by such increase. 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 evolution 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 existence, 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 circumstances 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 individual are developed at the expense of modes of conduct having an opposite 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 obvious that whatever conduct causes contests (whether for life or subsistence) within the race or species, tends to the elimination of members 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 individual 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 developed 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 creatures may possess. In fact, the Protozoa multiply by dividing. We
