After seeing the movie, John Gibbons, a herpetologist (reptile scientist) at the University of the South Pacific, realized that the iguanas that appeared in the film were a distinct species that had never been seen or documented by scientists before. Afterwards, Gibbons visited Nanuya Levu, the Fiji Island where the movie was made, and named the species the Fiji Crested Iguana.
It was the director's original concept to have the two grown characters play the entire film in the nude, which scared off many actors (including Jennifer Jason Leigh, who was the first choice for the female lead.) After Leigh passed on the project, the producers offered Diane Lane and Willie Aames the film after screen-testing them together in Mexico, where Lane was shooting a western...but the pair discussed the nudity together after the crew left and called a few days later to say they wouldn't do the film, either. With shooting set to begin in a matter of days, the desperate director agreed to let Shields make the film predominantly clothed, with a body double employed for the nude scenes. With that settled, the casting director returned to the thousands of audition tapes they'd made over the course of a year, and decided Christopher Atkins would be alright if he permed his hair to look more "savage."
Because of the belief that the "heroic man is supposed to be taller than the woman", Brooke Shields spent much of this movie walking in trenches dug into the beach. This was due to the fact that, despite being only 14 (compared to Christopher Atkins' 18 years), Brooke Shields was already 5'10", dwarfing Chris Atkins height of 5'6". Years later, they would appear on an awards show, this time she standing her full adult height of 6', prompting his comment of "it's like having the 'Statue of Liberty' standing beside me".
Brooke's original body double broke her back, the replacement body double for Brooke Shields was originally hired to catch or train dolphins, she was the right body-type, so she was used as a nude double.
The double for Chris Atkins was initially one of the seaplane pilots flying staff and crew from the Fiji mainland to the island where the movie was shot. He did most of the nude scenes with Brooke Shield's double as well as a few of the minor stunts.