Professor Thorndike hits the nail on the head when he lays stress on the
intensity of activity in monkeys--activity both of body and mind. They
are pent-up reservoirs of energy, which almost any influence will tap.
Watch a cat or a dog, Professor Thorndike says; it does comparatively
few things and is content for long periods to do nothing. It will be
splendidly active in response to some stimulus such as food or a friend
or a fight, but if nothing appeals to its special make-up, which is very
utilitarian in its interests, it will do nothing. "Watch a monkey and
you cannot enumerate the things he does, cannot discover the stimuli to
which he reacts, cannot conceive the _raison d'etre_ of his pursuits.
Everything appeals to him. He likes to be active for the sake of
activity."
This applies to mental activity as well, and the quality is one of
extraordinary interest, for it shows the experimenting mood at a higher
turn of the spiral than in any other creature, save man. It points
forward to the scientific spirit. We cannot, indeed, believe in the
sudden beginning of any quality, and we recall the experimenting of
playing mammals, such as kids and kittens, or of inquisitive adults like
Kipling's mongoose, Riki-Tiki-Tavi, which made it his business in life
to find out about things. But in monkeys the habit of restless
experimenting rises to a higher pitch. They appear to be curious about
the world. The psychologist whom we have quoted tells of a monkey which
happened to hit a projecting wire so as to make it vibrate. He went on
repeating the performance hundreds of times during the next few days. Of
course, he got nothing out of it, save fun, but it was grist to his
mental mill. "The fact of mental life is to monkeys it own reward." The
monkey's brain is "tender all over, functioning throughout, set off in
action by anything and everything."