Today we're going to point the skeptical eye into the world of anthropology, and shine the light of science around to see what we can learn about one of the fringe theories put forth to explain human evolution. It's been promoted on the stage in a 2009 TED talk; it was the underlying theory of Animal Planet's 2011 documentaryMermaids: The Body Found; and it was even described in Desmond Morris' famous 1967 nonfiction book The Naked Ape. It is the aquatic ape theory, an idea first widely publicized by marine biologist Alister Hardy in the 1930s. Its intent is to explain the reason humans are so different from the other great apes. While the other great ape species stayed on land and retained their fur, their knuckle walking, and their lean mass, humans became hairless, upright, and fat as an adaptation to being — for some two million years — an aquatic mammal.

The aquatic ape theory was an attempted explanation for why humans differ so much from the other great apes. Hominids all diverged from common ancestors, butHomo sapiens more radically so. We walk upright all the time, we don't have fur, we have bigger brains and are less robust, and so on. A number of people throughout history have noted that there must have been some evolutionary pressure on our line that wasn't on the others. Hardy was among the first to point this out at length, and his notion was that all these major differences are best accounted for if the Homogenus (after our evolutionary split from chimpanzees) went through an aquatic, or at least amphibian, stage. The idea's principal proponent since Hardy has been British screenwriter Elaine Morgan, who has written at least six books promoting the aquatic ape theory as a valid, if not superior, alternative to the standard model of human anthropology which has found that the Homo divergences are the result of adaptations for moving from the trees to the savannah.