The characteristic feature of social behaviour is that it is in large degree determined by the behaviour of other members of the social community. In all animals which mate there is a temporary or more lasting influence on each other of the individuals which unite to procreate their kind; and in those which foster their young there is a social relation of parents and offspring. Some of these mutual relationships will be discussed, in their emotional aspects, in the next chapter. Here we will consider the more general factors which serve to determine the course of social evolution. Among these is commonly reckoned imitation. M. Tarde says, “La société c’est l’imitation.” But this word, like so many others which are employed alike in popular speech and in more or less technical discussions, carries a somewhat wide range of meaning, and is by some writers used in a broader, by others in a narrower sense. Thus Professor Mark Baldwin[74] says, “that all organic adaptation in a changing environment is a phenomenon of _biological_ or _organic imitation_,” under which category will fall, therefore, the organic behaviour of the protozoa and of plants. On the other hand, Professor E. L. Thorndike, though he admits in the lower animals “certain pseudo-imitative or semi-imitative phenomena,” has been led by experiments, to be presently noticed, to the conclusion that animals as high in the scale of life as cats and dogs cannot form new associations under the influence of imitation. “It seems sure,” he says,[75] “from these experiments, that the animals were unable to form an association leading to an act from having seen another animal, or animals, perform the act in a certain situation.” In face of such apparently diverse usage it is necessary to show within what limits and with what qualifications the word may profitably here be used to indicate a factor in social evolution.