For those interested, here's the citation for the article I mentioned earlier. You can read it, along with a reply by Nevins et al., as a pdf for free here:
Everett, Daniel (2005b), "Cultural Constraints on Grammar and Cognition in Pirahã," Current Anthropology, Volume 46, Number 4, August-October.
Dan Everett's most recent reply to Nevins et al. (2007) is available for free here.
Language Log has quite a few posts on the Everett-Nevins controversy. For those who want the quick-and-dirty on the innumeracy issue, here's the first graph of a recent post by Geoff Pullum:
The Pirahã language and culture seem to lack not only the words but also the concepts for numbers, using instead less precise terms like "small size", "large size" and "collection" . And the Pirahã people themselves seem to be suprisingly [sic] uninterested in learning about numbers, and even actively resistant to doing so, despite the fact that in their frequent dealings with traders they have a practical need to evaluate and compare numerical expressions. A similar situation seems to obtain among some other groups in Amazonia , and a lack of indigenous words for numbers has been reported elsewhere in the world.
When I have more time, I might compare the Plato text with Everett's articles, to see how their claims line up in light of Estelle's comment in class.
John.