Psychology no longer confines itself, as it formerly did, to the human soul, denying to the animals a place in this highest of all the sciences.

It finds itself unable to require any test or evidence of the presence of mind which the animals do not meet, nor does it find any place at which the story of the mind can begin higher up than the very beginnings of life.

For as soon as we ask, "How much mind is necessary to start with ?" we have to answer, "Any mind at all"; and all the animals are possessed of some of the actions which we associate with mind.

Of course, the ascertainment of the truth of this belongs--as the ascertainment of all the truths of nature belongs--to scientific investigation itself.

It is the scientific man's rule not to assume anything except as he finds facts to support the assumption.