Primal Shadows — Alan Dean Foster

His wallet stolen by a one-night-stand, Bohannon still believes her to be the girl of his dreams. This weary world traveler decides as a matter of honor that he must pursue her. Recruiting a scout from the roughneck Caucasian castoffs of the New Guinea port he pursues her farther and farther up country, to areas where headhunters still roam and law and order play by entirely different rules.

Beyond the natural threats of poisonous reptiles and bugs, floods, and the jungle, Bohannon encounters the various evils of men, as he winds up in the middle of a hunt for gold that proves that more than lust or love, greed is man's most primal instinct.