The People in the Trees - Hanya Yanagihara

In 1950 Norton Perina, a young doctor, embarks on an expedition to a remote Micronesian island in search of a rumoured lost tribe. There he encounters a strange group of forest dwellers who appear to have attained a form of immortality that preserves the body but not the mind. Perina uncovers their secret and returns with it to America, where he soon finds great success. But his discovery has come at a terrible cost, not only for the islanders, but for Perina himself.