Page:Popular Science Monthly Volume 71.djvu/80

80 always is: Whose descendants are to represent the future of the species? The question is one. But a decision may be rendered at any of several different points.

The three forms of selection so far mentioned apply to individuals. Group selection is recognized by Darwin, though not treated separately, nor by him distinguished from natural selection. Group selection results where a number of individuals act and suffer jointly, whether with conscious purpose or not, in matters affecting their success and survival in competition with other groups. It is selection operating groupwise.

We have distinguished three forms of selection of individuals, over against which is now set group selection. It may appear that we should make a triple division of group selection, as we have of the selection of individuals. It is obvious, however, that the concept of sexual selection is entirely inapplicable. A group does not propagate its kind by a sexual relation with another group. Reproduction, of course asexual, might be predicated of a group. The idea of reproduction, however, as applied to the group, is but an analogy; and where so applied, it is of little or no significance for selection. Eeproduction of its individuals is not reproduction of the group, for the group remains the same while its members change, just as does the body while its component cells die and are replaced by others. The group is thus potentially immortal and does not regularly reproduce itself. Wlien a successful group becomes unduly large, it may divide or send out a "daughter colony," thus, so to speak, propagating itself by fission. But this is a question of size, not of differences in degree of natural reproductivity on the part of groups. As regards the "decease" of such a selectional group, moreover, it comes either by dissolution, that is, by the loosening of its bands and the dropping away of its members, or by their physical death. In the former case selection has not yet completed its work. In the latter case its work has taken an individual form. The ultimate incidence of group selection is always on individuals, affecting them either in the duration of their life or in their reproduction. But the effect is likely to be compound. From which of these two sorts of selection it comes, and how much is from one or the other form, are questions which have little importance from the point of view of the group. Therefore, if it is possible, it is not worth while, to attempt to subdivide group selection into lethal and reproductive forms.

Group selection is logically coordinate with all three of the other forms. In practise, however, taking account of its degree of importance, as well as of the fact that it is not to be subdivided, we may