A squirrel is just as clever as it needs to be and no more; and of some
vanishing mammals, like the beaver, not even this can be said. Humdrum
non-plastic efficiency is apt to mean stagnation. Now we have just seen
that in the play of young mammals there is an indication of unexhausted
possibilities, and we get the same impression when we think of three
other facts. (_a_) In those mammals, like dog and horse, which have
entered into active cooperative relations with man, we see that the mind
of the mammal is capable of much more than the average would lead us to
think. When man's sheltering is too complete and the domesticated
creature is passive in his grip, the intelligence deteriorates. (_b_)
When we study mammals, like the otter, which live a versatile life in a
very complex and difficult environment, we get an inspiriting picture of
the play of wits. (_c_) Thirdly, when we pass to monkeys, where the
fore-limb has become a free hand, where the brain shows a relatively
great improvement, where "words" are much used, we cannot fail to
recognise the emergence of something new--a restless inquisitiveness, a
desire to investigate the world, an unsatisfied tendency to experiment.
We are approaching the Dawn of Reason.