An update on the Pirahã
The Pirahã are a tribe of Amazonian Indian who have become famous among linguists and psychologists because it has been claimed that they lack a number system (not even a word for one), recursion, and color words (and they seem to be a very happy people despite the absence of Louis Vuitton shops, something I dare not believe).
Dan Everett, an ex-missionary/linguist/anthropologist, is one of the few people to speak their language, and he is responsible for most of the provocative claims about the Pirahã (see for instance this paper in Current Anthropology). A few months back, he published an autobiographical description of life among the Pirahã, accompanied by a popular science account of his discoveries: Don't Sleep There Are Snakes.
Given that I have no expertise in linguistics, I can only point to the published debates. Here is an attack on Everett's claims and here is his answer. In any case, the book makes for a very pleasing read.
As a psychologist of reasoning, I was surprised to learn that the Pirahã, as well as having no number system seem to have no explicit disjunction, conjunction, conditional or quantifier either. Apparently though that does not stop them from arguing quite a lot among themselves and with Everett (who once had to talk his way out of a very threatening situation).
On the topic of the Amazon, I can't help mentionning this very entertaining book that recently came out: The Last City of Z (by David Grann). It tells both the tale of the last great Victorian explorer who disappeared in the Amazon in the 20's and of the author trying to retrace his steps. Grann also brushes over some of the amazing findings of Michael Heckenberger and other anthropologists/archeologists who claim to have discovered the remnants of an ancient civilization in the depth of the Amazonian forest (see 1491 for a very good account of these findings).