What's more, they seem to be natural rationalists:
"The Pirahã language is the simplest in the world. Speaking it and singing it are the same, and it can be hummed or even whistled, yet it can convey enormous richness. Among other things, the wide variety of verb forms are used to account for the directness of evidence for a statement. Everett originally went to the Pirahã in 1977 as a Christian missionary. They challenged him to provide evidence for the existence of Jesus, and lost interest when he couldn’t. Eventually so did he. The Pirahã made him an atheist." (emphasis added)
More importantly, their language is under threat of disappearing entirely as the Pirahã's ecosystem rapidly disappears.