The People in the Trees

In 1950, a young doctor called Norton Perina signs on with the anthropologist Paul Tallent for an expedition to the remote Micronesian island of Ivu'ivu in search of a rumored lost tribe. They succeed, finding not only that tribe but also a group of forest dwellers they dub "The Dreamers," who turn out to be fantastically long-lived but progressively more senile. Perina suspects the source of their longevity is a hard-to-find turtle; unable to resist the possibility of eternal life, he kills one