I posted the following in 2008:

Although linguist Daniel Everett has been studying the Pirahã (pronounce pee-da-ha) Amazonian tribe, and their unique language since the 1970’s, his work remained relatively obscure until 2005, when an article he’d published on his website was then published in Cultural Anthropology.  According to Everett’s studies, the Pirahã’s language lacks many aspects of language that linguists argue are basic necessities of a universal grammar, such as color concepts, perfect tense, quantity concepts, and numbers over two.  Why?  According to Everett, their hunter-gatherer lifestyles have such little use for these concepts, that words to convey them simply don’t exist.  This research, which overtly repudiates the Chomskyian theory that has dominated the study of language for decades, has been called by Steven Pinker, “A bomb thrown into the party.”

The coverage of this study has greatly expanded recently, exemplified by this New Yorker article.  Language Log has some excellent links concerning the Piraha.

Daniel L Everett (right): Photograph: Martin Schoeller Martin Schoeller/PR from http://www.theguardian.com/technology/2012/mar/25/daniel-everett-human-language-piraha

Update:  The debate caused by Everett’s studies of the Pirahã , and the continuance of this debate is fascinating.  Those supporting universal grammar seem hung up on attacking Everett’s methodology, which are offered up as evidence that his conclusions are false.  Interestingly, the Sapir-Whorf hypothesis was practically discarded for years because of Benjamin Whorf’s misleading claims about the number of words Inuit Eskimos had for snow.  It should be noted that it has been far from proven that Everett’s methods actually were problematic.  Meanwhile, the consensus appears to be favoring the truth as lying somewhere between linguistic relativism, or what is sometimes called the strong Sapir-Whorf hypothesis, and claims that all of language is determined by structures born into our brains.

Everett’s quote from this story excellently sums up what I think is closest to the truth:  

“The lesson is that language is not something mysterious that is outside the bounds of natural selection, or just popped into being through some mutated gene. But that language is a human invention to solve a human problem. Other creatures can’t use it for the same reason they can’t use a shovel: it was invented by humans, for humans and its success is judged by humans.”