Sharing a name with what was once the largest Indian tribe in the Amazon region, the Guarani is also Paraguay's currency.

NPR: What's In a Nickname? The Answer Is in the Cup

The Piraha, a tribe in the Amazon in Brazil, whose language eschews number words in favor of terms like few and many, are not able to keep track of exact quantities.

WSJ: Does Language Influence Culture?

In 2004, Carolina Izquierdo, an anthropologist at the University of California, Los Angeles, spent several months with the Matsigenka, a tribe of about twelve thousand people who live in the Peruvian Amazon.

NEWYORKER: Spoiled Rotten