It is often noted that humans differ from chimpanzees by less than 2% of their DNA. But within that small percentage, one singular difference is human speech and language. To varying degrees, chimpanzees have been taught some signs from sign and artificial languages. But chimpanzee language is not like natural child language. The science of speech and language is known as linguistics. With astronomy, linguistics is one of the two oldest sciences. 

Speech and language are not the only difference between humans and chimpanzees. But speech and language are a special case. There is both an infinite capacity and a commonality across all members of the species. On the infinity, sentences can be lengthened indefinitely, as by “What are you saying?” “I know what you’re saying”, “They think that I know what you’re saying”, “She suspects that they think that I know what you’re saying”, and so on. And there is commonality in the fact that this is reliably understandable. The understandability declines as the length and complexity increases. But there is no point at which the structure ceases to be English, as just one arbitrarily selected human language. No non-human has ever shown any awareness of the little word that in structures like “They think that I know what you’re saying”. In some languages, English being one, it is not pronounced, as in “They think I know”, but pronounced in “They think that I know ”. In this, the commonest sort of case, that in English is optional. But the possibility of using it opens up both the infinity and the commonality. The device or devices which allow language to have these capacities include syntax.

By the age of three children are growing their lexicons by 10 or so new words every waking hour, more in a week than any non-human in a life time, and not just asking and understanding questions, but saying things like “I want to stand on the chair to see what’s happening”, with three bits of sentences embedded inside one another, with I understood as the subject of three of the verbs, but pronounced as the subject of just the outermost verb in the structure. I is is displaced twice, as the underlying subject ot see and of stand, One of the subjects of the research here said this just before he was three. The other subject said something similar at the same age. To explain this on the basis of a simple stringing together would be more complex than by repeating the same sorts of structure and then assembling them into one larger structure of the same fundamental sort.

This implies a significant inherited capacity. Randulf Quirke (1972) drew attention to the therapeutic significance of this line of investigation as pioneered by Noam Chomsky (1957, 1965, 1968 and other work) and Eric Lenneberg (1969) with a final chapter by Chomsky. But any inherited capacity is vulnerable. Hence speech and language defects and the website here.