Such a theory has recently been developed.

It holds that the plays of the animals are of the greatest utility to them in this way: they exercise the young animals in the very activities--though in a playful way--in which they must seriously engage later on in life.

A survey of the plays of animals with a view to comparing them in each case with the adult activities of the same species, confirms this theory in a remarkably large number of cases.

It shows the young anticipating, in their play, the struggles, enjoyments, co-operations, defeats, emergencies, etc., of their after lives, and by learning to cope with all these situations, so preparing themselves for the serious onset of adult responsibilities.

On this theory each play becomes a beautiful case of adaptation to nature.