In the mid-90's, I did a part-time course in teaching English as a foreign language at Manchester College of Arts and Technology. One of things we studied was theories of language acquisition and it's something I've been fascinated by ever since. The mainstream theory of language aqcquisition since the 1970's - developed by Noam Chomsky, Stephen Krashen, Stephen Pinker and others - is centred on the idea of a Language Acquisition Device (LAD), a innate genetically transmitted ability unique to humans which allows children to instinctively learn their native language. This means that grammatical features (tenses, plurals etc.) appear in children at the same time whatever that language is.
I was interested therefore to read about a new book by one Daniel Everett which apparently seeks to overturn the LAD theory of language acquisition on the strength of a language called Pirahã spoken by around three hundred people in the Amzonian region of Brazil and which Everett claims doesn't include these grammatical features.
There are a number of holes that can be put in Everett's claims: he is the only non-native speaker of Pirahã and there is no way of knowing if what he says about the language is true (even if he thinks it is, there is no saying that the he has picked up all its nuances from the native speakers). He also seems to have oversimplified what Chomsky says about language acquisition in order to try to knock his theories down. But the killer point to me - and one the Guardian review doesn't really deal with, possibly for reasons of undue politeness or liberal sensibilities - is that Everett is an evangelical Christian and former missionary who travelled to Amazonia to convert the native peoples and whose only reason for learning Pirahã was to translate the Bible into it. Whatever Chomsky's political faults, I'd trust his rational judgements on language acquisition over Everett's any day of the week.