The mermaid legend has been around since before the Romans ruled the earth, and even back then, guys were asking the same question: How did these womanly fish have sex?
It's a question that dogged filmmaker Charlie Foley when he started work on "Mermaid: The Body Found," a speculative documentary airing May 27 and 28 on Animal Planet -- from his own father, no less.
"It was the first thing my dad asked me when I told him about the special," Foley laughed to The Huffington Post. "We had to think about this, and I assume that mermaid sex organs would evolve like those of whales, seals and porpoises. Their bodies are streamlined, but those parts 'pop out' when needed."
Sorry, fish fetishists, the special doesn't show mermaids and mermen splashing around in icthyological intercourse, but there is a scene of a CGI mermaid giving birth.
Foley isn't saying that mermaids exist, but finds it fascinating that the comely sea creatures have been talked about for thousands of years and show up in the writings of numerous cultures -- even among cultures that had no contact with each other.
There has never been a confirmed mermaid sighting, and some researchers speculate that people who've claimed to have seen one outside of a movie theatre actually saw creatures like manatees or dugongs.
However, some researchers have suggested the "Aquatic Ape Theory." They claim that during a period of massive coastal flooding, some ancestors moved inland and others went into the ocean for food.
The theory forms the basis of the show and while the idea that mermaids might be real may sound absurd on the surface, filmmaker Charlie Foley says further study suggests it might not be all wet.
"There are cases of animals going from terrestrial to aquatic," Foley told The Huffington Post. "And when you look at what makes humans unique among other terrestrial animals, it raises some interesting questions on whether mermaids might be plausible."
MERMAIDS THROUGH THE AGES GALLERY (Story continues below)
SPLASH, Daryl Hannah, 1984. (Buena Vista Pictures / Everett Collection)
This computer generated image courtesy of Disneyland Resort shows audio-animatronics characters from The Little Mermaid _ Ariel's Undersea Adventure attraction in Anaheim, Calif. This year, Disney California Adventure in Anaheim debuts The Little Mermaid _ Ariel's Undersea Adventure as part of a multiyear billion-dollar expansion of the park. The family-friendly ride features characters from the popular movie as riders travel on a virtual underwater journey. (Paul Hiffmeyer, Disneyland Resort / AP)
A reveler dressed as a mermaid poses for a photo at the annual Coney Island Mermaid Parade June 21, 2008 in the Brooklyn borough of New York City. One mermaid will launch a hunger strike following the parade to protest proposed development plans that critics say will ruin the amusement mecca's kitschy charm. (Mario Tama, Getty Images)
David Hasselhoff and the "Mermaid" stunt double race towards the beach on a jet ski during a scene filmed at Ehukai Beach Park on September 24, 2002 on the North Shore of Oahu, Hawaii. The scene is part of a Baywatch made for TV movie that is currently in production on Oahu. (Phil Mislinski, Getty Images)
The Little Mermaid statue 30th May 1957 in Copenhagen, Denmark. (Derek Berwin, Fox Photos / Getty Images)
Divers dressed as mermaids, perform at an aquarium at the Guangzhou Ocean World on August 3, 2005 in Guangzhou of Guangdong Province, south China. The "Mermaid Show" is one of most popular entertainments at the theme park, drawing a lot of tourists. The Guangzhou Ocean World, covering an area of about 13,000 square meters, with a total investment of USD 50 million, is a multi-functional scientific and technological exhibition hall that mixes together entertainment, appreciation, scientific research and education. (China Photos / Getty Images)
Circa 1200, A Danish Viking ship beset by mermaids. (Hulton Archive / Getty Images)
A model of a mermaid used in Harry Potter and the Goblet of Fire is displayed at the new Harry Potter Studio Tour at Warner Brothers Leavesden Studios on March 23, 2012 in London, England. The studio, which includes the actual sets and special effects departments where the films were created and shot, goes on public display on March 31, 2012. (Dan Kitwood, Getty Images)
Actress Sierra Boggess performs from "The Little Mermaid" onstage during the 62nd Annual Tony Awards held at Radio City Music Hall on June 15, 2008 in New York City. (Andrew H. Walker, Getty Images)
Visitors watch a woman acting like a mermaid as she swims with fish during a show at an aquarium in Beijing on June 13, 2009. The US wants China to accept slow increases in its greenhouse gas emissions until it hits a "peak year," beyond which a real decrease must occur, US negotiator Todd Stern said on June 12. (Liu Jin, AFP / Getty Images)
Performers from the Weeki Wachee Mermaids from the U.S. swim amongst fish during a full dress rehearsal for their upcoming ballet, in the Ocean Reef Display at the Sea Life Aquarium in London, on May 14, 2010. The underwater synchronized aquabatics troupe are set to perform for the public this weekend. (Ben Stansall, AFP / Getty Images)
A swimmer dressed in a mermaid costume performs at Chinagmai zoo aquarium in Chiang Mai province on August 3, 2010. Chinag Mai zoo aquarium is South East Asia 's largest living museum with nearly 20,000 examples of marine creatures. (Pornchai Kittiwongsakul, AFP / Getty Images)
Visitors in kayaks paddle around the sculpture "Giant Mermaid" on the Alster lake in the northern German city of Hamburg on August 2, 2011. The sculpture is created by art and advertising agency Oliver Voss. (Marcus Brandt, AFP / Getty Images)
Some of the evidence that Foley said could conceivably suggest a missing mermaid link include webbing between fingers, something other primates don’t have and the loss of body hair (which would create drag in water).
Other evolutionary steps that suggest a sea creature cousin include the fact that humans are the only land animal with subcutaneous fat, which helps insulate whales, seals and dolphins from the cold, and breath control.
"Humans can hold their breath up to 20 minutes, longer than any other terrestrial animal," Foley said. "In fact, we're the only land animal with an instinctive ability to swim."
Foley is quick to point out that he doesn't necessarily believe that mermaids existed, but, as he did with a previous special, "Dragons: A Fantasy Made Real," wanted to "plausibly imagine them."
To do that, he had to think about how a real mermaid would actually look -- and it's wouldn't be a red head like Ariel the Little Mermaid at all.
"Evolutionarily speaking, hair would be the first to go because it's a drag underwater," he said. "Also, we thought about the coloring. Sea mammals tend to have countershading. They are lighter on what, in layman's terms, would be the belly and darker on the back. This is so they would blend in with the water if you're looking at them from above and would blend in with the sun shining through the water if you're looking at them from below."
Foley hopes the special gets people interested in the Aquatic Ape Theory, but also admits that his goal isn't to win converts to the idea."This is meant for entertainment," he laughed. "We didn't submit this for peer review."