The River of Doubt by Candice Millard

Great book about the 1913 expedition with former Pres Teddy Roosevelt and his son to explore an unmapped river in Brazil's Amazon rain forest.
The book details the struggles the expedition faces with unforgiving forest weather and wildlife of the region with then modern equipment. In comparison the book references native indian tribes in the region who survive and thrive in this area with a stone age existence.

One interesting note is their search for food to supplement their rations and the most prized is the elusive Brazil nut beacause of its healthy fat content.