These would secure the combination of the two groups of
movements, which I have assumed to have been employed
independently as utterances of pleasurable feeling : namely,
those involved in smiling, and those underlying the first
happy reiterated sounds of a quasi-infantile babbling.
176 THE ORIGIN OP LAUGHTER

One element in the laugh, its explosive vigour, seems
unaccounted for on this hypothesis. Here, I think, the
eifect of relief from strain, which is so common a factor in
human laughter, may be called in. The earliest laughter
of the child seems to illustrate this element. For example,
that which occurs during tickling, in a game of bo-peep,
and at the sight of the mother makiag faces may be said to
arise from a serious attitude suddenly dissolved. Perhaps
the first great laugh was produced by man or by his
proximate progenitor, when relief came after fear or the
strain of battle. So far as primitive laughter was the out-
come of such concentrated energy seeking relief, this circum-
stance would help to account for the prolongation as well
as for the strength of the sounds.
Our conjecture cannot lay claim to be a hypothesis. It
makes no attempt to explain the precise forms of the
changes which enter both into the smile and into the laugh.
At best, it is only a rough hint as to a possible mode of
genesis.
