La Mettrie (1748/1912) equated intelligence and some personal- ity characteristics with the size and quality of the brain:
I shall draw the conclusions which follow clearly from … incontestable observa- tions: 1st, that the fiercer animals are, the less brain they have; 2nd, that this organ seems to increase in size in proportion to the gentleness of the animal; 3rd, that nature seems here eternally to impose a singular condition, that the more one gains in intelligence the more one loses in instinct.
If humans can be considered superior to non- human animals, it is because of education and the development of language. Because the primate brain is almost as large and as complex as ours, it follows that if primates could be taught language, they would resemble humans in almost all respects. The question is, can primates learn a language?
Among animals, some learn to speak and sing; they remember tunes, and strike the notes as exactly as a musician. Others, for instance the ape, show more intelligence, and yet can not learn music. What is the reason for this, except some defect in the organs of speech? In a word, would it be absolutely impossible to teach the ape a language? I do not think so.