But how are we to know when to credit the animal with intelligence and
when with something less spontaneous? Above all, how are we to know when
the effective action, like opening the mouth the very instant it is
touched by food in the mother's beak, is just a physiological action
like coughing or sneezing, and when there is behind it--a mind at work?
The answer to this question is no doubt that given by Prof. Lloyd
Morgan, who may be called the founder of comparative psychology, that we
must describe the piece of behaviour very carefully, just as it
occurred, without reading anything into it, and that we must not ascribe
it to a higher faculty if it can be satisfactorily accounted for in
terms of a lower one. In following this principle we may be sometimes
niggardly, for the behaviour may have a mental subtlety that we have
missed; but in nine cases out of ten our conclusions are likely to be
sound. It is the critical, scientific way.
Bearing this law in mind, let us take a survey of the emergence of mind
among backboned animals.