Animal Planet/Mermaids On Sunday, Animal Planet aired a follow-up to last year's television special called "Mermaid: The Body Found."

The two-hour documentary-style program — described by the network as "science fiction based on some real events and scientific theory" — was so convincing that the National Oceanic and Atmospheric Administration was initially overwhelmed by callers demanding to know the truth about the existence of the legendary sea creatures.

There is no scientific evidence that mermaids exist, but the way the story is told, it is often difficult to separate fact from fiction.

There's been some uproar about it airing on "Animal Planet," a channel that traditionally focuses on nature and science, rather than myth and fantasy.

Charlie Foley, the show's executive producer, creator, and writer, encourages viewers to approach the show with a sense of possibility, with the understanding that the storyline is meant to be entertaining too.

The mockumentary uses evolution-based theories and several real examples from nature as a springboard to weave an imaginary story about a contemporary myth, Foley said.

Here's the story of how mermaids evolved from humans as told in the special.