One other early form of laughter, which is found also in certain young animals, is that excited by tickling. This has been first observed, in the case of the child, in the second or the third month. Preyer’s boy laughed in response to tickling in the second month.[106] Dr. Leonard Hill tells me that his little girl, who was by-the-bye specially sensitive to titillation, responded first by laughter in the tenth week.
Since our analysis has led us to regard the effect of tickling as largely mental, and as involving a playful attitude, this fact confirms the conclusion that the specialised laughter which is the accompaniment of play occurs in a well-defined form within the first three months.
To sum up: We find, within the first two or three months, both the smile and the laugh as expressions of pleasure, including sensations of bodily comfort and gladdening sense-presentations. We find, further, in the reflex reaction of laughter under tickling, which is observable about the {170} end of the second month, the germ of a sense of fun, or of mirthful play; and this is indicated too in the laughter excited by little pinches on the cheek at the end of the third month.
It is certain that these tendencies are not learned by imitation. This is proved by the fact, established by Preyer, that imitative movements do not occur in the normal child till considerably later, and by the fact that the child, Laura Bridgman, who was shut out by her blindness and deafness from the lead of companions, developed these expressions. We must conclude, then, that they are inherited tendencies.
Here the psychologist might well stop in his inquiries, if Darwin and others had not opened up the larger vista of the evolution of the species. Can we, by carrying the eye along this vista, conjecture how these instinctive movements came to be acquired in the course of animal evolution?
The first question that arises in this inquiry is whether the smile or the laugh was the earlier to appear in the course of racial development. The expressions of animals below man do not offer any decisive clue here. The anthropoid apes appear both to produce a kind of smile or grin, and to utter sounds analogous to our laughter. It may, however, be contended that this so-called laughter is much less like our laughter than the grin is like our smile. In the absence of better evidence, the fact that the smile appears first in the life of the child must, according to a well-known law of evolution, be taken as favouring the hypothesis that man’s remote ancestors learned to smile before they could rise to the achievement of the laugh. This is further supported by the fact that, in the case of the individual, the laugh when it occurs announces a higher form of pleasurable consciousness, the level of perception {171} as distinguished from the level of sensation which is expressed by the first smile. Lastly, I am informed that among imbeciles the smile persists lower down in the scale of degeneration than the laugh. Dr. F. E. Beddard writes to me: “I remember once seeing a defective human monster (with no frontal lobes) whose only sign of intelligence was drawing up the lips when music was played”.[107]
It is commonly held that, since the expression of pain, suffering, or apprehension of danger among animals is a much more pressing necessity for purposes of family and tribal preservation than that of pleasure or contentment, the former is developed considerably earlier than the latter. According to this view, we can understand why the adumbrations of a smile and a laugh which we find in animals closely related to man have been so imperfectly developed and appear only sporadically.
Supposing that the smile was the first of the two expressive movements to appear in the evolution of the human species, can we conjecture how it came to be the common and best-defined expression of pleasurable states? In dealing with this point we may derive more definite aid from Darwin’s principles.
The fact that the basis of a smile is a movement of the mouth at once suggests a connection with the primal source of human as of animal enjoyment; and there seems, moreover, to be some evidence of the existence of such a connection. A baby after a good meal will, I believe, go on performing something resembling sucking movements. The first smiles may have arisen as a special modification of these movements when there was a particularly lively feeling of organic contentment or well-being. I believe, further, {172} that an infant is apt to carry out movements of the mouth when food is shown to it. A similar tendency seems to be illustrated by the behaviour of a monkey which, when a choice delicacy was given it at meal-time, slightly raised the corners of the mouth, the movement partaking of the nature of “an incipient smile”.[108] Again, our hypothesis finds some support in the fact that, according to Preyer and others, the first smiles of infants were noticed during a happy condition of repletion after a good meal.[109]
Supposing the smile in its origin to have thus been organically connected with the pleasurable experience of sated appetite, we can easily see how it might get generalised into a common sign of pleasure. Darwin and Wundt have made us familiar with the principle that expressive movements may be transferred to states of feeling resembling those of which they were primarily the manifestations. The scratching of the head during a state of mental irritation is a well-known instance of the transference.