Page:Popular Science Monthly Volume 81.djvu/562

556 and series of combinations of reflex reactions in the presence of a series of complex stimulations appeared and these in turn were rendered more complex by the development of habits based on individual experiences repeated anew by every generation. Each useful instinct and every valuable habit made the individual organism more efficient, lessened the effort necessary to live, increased surplus energy.

As man was approached, however, the factor of habit became more and more important. Some hint of how this occurred may be gained from every-day observation. It is a commonplace that exercise of muscles that are fitted to perform certain functions renders the habitual exercise of that function as certain in its operation as is a pure reflex. Young birds awkward in their first flight become expert rapidly. Beasts of prey by trial and error eliminate unsuccessful modes of attack. Before our eyes instinctive actions become modified by experience to a very appreciable extent. Tricks are even taught to seals, lions and elephants, and finally habits useful to man are learned by horse and dog. Thus man has appropriated to his own use the surplus energy developed in the higher animals and has profited thereby immensely.

But the stage of advance now under discussion is that of man's immediate precursors when they, too, had merely learned to profit by past experience through the method of trial and error and elimination of unsuccessful activities.

At this point doubtless the objection will be made that other functions affecting surplus had by this time appeared in man's precursors. It will be held that imitation, at least, was present far down the scale. Certainly it must be granted that any tendency of an organism A to imitate a useful innovation of a similar organism B would, in most instances, increase the surplus possessed by organism A. A flock of birds may take flight if a single bird flies away in alarm. This may be an advantage to every member of the flock. It is necessary, however, to distinguish sharply at least two kinds of imitation. Instinctive imitation, of which the case of the birds which fly when one of the flock takes wing may be taken as an instance, occurs when the sight or sound of one animal's performing a certain act operates as a direct stimulus to the performance of a similar act by another animal whose organization is such as naturally to lead to that act by reflex response whenever the appropriate stimulus is given. The model-act releases the trigger, the organism does the rest by reflex action in accordance with inherited functions. The second type of imitation occurs only when the model-act suggests to the observer the feeling of pleasure or the idea of utility that would result if he repeated the act for himself. The process involved in the first type appears to be no different from those which occur when an animal responds to any stimulus whatsoever. The function is reflex in accordance with the inherited structural organization