We are considering the functions of the body when we are inquiring into such actions of the various structures internal and external as involve internal processes, simple or complex. But, when we begin to consider combinations of actions externally manifested, we are dealing with conduct—except only in the case of such actions as are independent of control.
But at the outset of the evolution of conduct even this distinction is scarcely to be recognized. Every external combination of actions is in the lower types of animal life a part of conduct at least of such conduct as is possible in the lowest orders of creatures. Evolution of conduct begins with the gradual development of purpose where at first actions were random and aimless. The Amœba wanders from place to place, not by the action of limbs, but by a process which may be called diffluence. In so doing it may come into the neighborhood of objects fit to form its food; these it inwraps, and absorbing what is digestible rejects the rest. Or its wanderings may lead it into the way of some creature by which it is itself absorbed and digested. There may be some higher law than chance guiding the movements of such creatures; but so far as can be judged this is not the case. In other words there is but the suspicion of something like conduct in the actions of the Amœba. Among other creatures belonging to the same kingdom, but higher in type, we find actions so much better adjusted, that, though even yet we can not recognize such evidence of purpose as enables us to describe their actions as conduct, we yet see in their adjustment to certain ends the development of something akin to conduct. The actions seem guided by what mimics purpose if it is not purpose itself.
Now, we note that with the improved adjustment of actions comes an increase in the average duration of life, or rather in the proportion of this average to the length of life possible among these several creatures.
So when we pass to higher and higher orders of animals, we find in every case among the lower types irregular and seemingly purposeless actions, while among the higher we find actions better adjusted to the surroundings. And, again, we note that, where the combination of actions, or what we may now call the conduct, is not adjusted to the environment, the creatures' chances of life are small, great numbers dying for each whose life approaches the average duration. An improved adjustment of conduct to environment increases the chances of survival, many attaining and some passing the average of longevity in their particular type or order.
Now, structural development is guided by the fitness or unfitness of particular proportions in such and such structures for the great life-struggle in which all animal life is constantly engaged; and functional development is guided by the corresponding fitness or unfitness of such and such functional activities. Just as certainly the development of
