A glimpse of what mammals are capable of, were it necessary, may be
obtained by watching those that are playful, such as lambs and kids,
foals and calves, young foxes and others. For these young creatures let
themselves go irresponsibly, they are still unstereotyped, they test
what they and their fellows can do. The experimental character of much
of animal play is very marked.
It is now recognised by biologists that play among animals is the young
form of work, and that the playing period, often so conspicuous, is
vitally important as an apprenticeship to the serious business of life
and as an opportunity for learning the alphabet of Nature. But the
playing period is much more; it is one of the few opportunities animals
have of making experiments without too serious responsibilities. Play is
Nature's device for allowing elbow-room for new departures
(behaviour-variations) which may form part of the raw materials of
progress. Play, we repeat, gives us a glimpse of the possibilities of
the mammal mind.