[aomurphy]

Not knowing what to believe is probably the best thing right now. Everett (the linguist who made the claims) is quite insistent that this is the case, many other linguists are not. It's definitely a big controversy right now, particularly Everett's claim that Piraha does not allow recursion (many linguistic theories, notably Chomsky's, seem to make recursion a pretty fundamental feature of human language). A lot of the arguments are pretty technical, and they're all ham strung by the fact that the Piraha are so remote there isn't a whole lot of research on them besides Everett's, and even he has trouble going back now.

This blog post has a nice set of links about the controversy, and Everett and one of his major critics both appear in the comments to argue, so definitely read those if you are interested:

http://languagelog.ldc.upenn.edu/nll/?p=3857

[WaxProlix]

When you have one data source and only a handful of data points and that data is not reproducible, you're not doing science. Everett might have some interesting hypotheses, but what he's doing isn't what you could call peer-reviewable. Linguists who have aspirations towards hard science will, for that reason alone (not to mention the theoretically tenuous/unpopular nature of his claims) dismiss him pretty quickly.

[zorked]

While it is far more likely that Everett is wrong, science has to start somewhere, and Pirahã people exist on this planet and other people could go check the story. You can absolutely prove him wrong.

Coming up with crazy ideas based on some strange observations is a part of science too.

[WaxProlix]

And questioning that, pointing out flaws and questioning methodology, is all science, too.

It's just convenient that Everett had the only 'in' with the community and so is the de facto expert. Once the data source is available, we'll know more.

[meepmorp]

Off topic, but it's pretty funny to watch Everett give a talk to a room full of generative-trained syntacticians, just to see how angry everyone gets during the Q/A section.

[proveanegative]

Why is Everett prohibited from going back?