Aquatic ape

The **aquatic ape hypothesis** (**AAH**), also referred to as **aquatic ape theory** (**AAT**) and more recently the **waterside model**, is the idea that certain ancestors of modern humans were habitual waders, swimmers and divers. The hypothesis in its present form was proposed by the marine biologist Alister Hardy in 1960, who argued that a branch of apes was forced by competition over terrestrial habitats to hunt for food such as shellfish on the sea shore and sea bed leading to adaptations that explained distinctive characteristics of modern humans such as functional hairlessness and bipedalism.

This proposal was built upon by Elaine Morgan in her 1972 book *The Descent of Woman*.

## History

The German pathologist Max Westenhöfer (1871–1957) discussed in 1942 various human characteristics (hairlessness, subcutaneous fat, the regression of the olfactory organ, webbed fingers, direction of the body hair etc.) that could have derived from an aquatic past, quoting several other authors who had made similar speculations. He stated: "The postulation of an aquatic mode of life during an early stage of human evolution is a tenable hypothesis, for which further inquiry may produce additional supporting evidence."

## The Hardy/Morgan hypothesis

Independently of Westenhöfer's writings, the marine biologist Alister Hardy had since 1930 also hypothesized that humans may have had ancestors more aquatic than previously imagined. On the advice of his colleagues, Hardy delayed presenting the hypothesis for approximately thirty years. After he had become a respected academic and knighted for contributions to marine biology, Hardy voiced his thoughts in an article in *New Scientist* on 17 March 1960.

Hardy's hypothesis as outlined in the *New Scientist* was:

My thesis is that a branch of this primitive ape-stock was forced by competition from life in the trees to feed on the sea-shores and to hunt for food, shell fish, sea-urchins etc., in the shallow waters off the coast. I suppose that they were forced into the water just as we have seen happen in so many other groups of terrestrial animals. I am imagining this happening in the warmer parts of the world, in the tropical seas where Man could stand being in the water for relatively long periods, that is, several hours at a stretch.
Hardy argued a number of features of modern humans are characteristic of aquatic adaptations. He pointed to human's lack of body hair as being analogous to the same lack seen in certain other marine mammals, such as the whale and the hippopotamus, and noted the layer of subcutaneous fat humans have that Hardy believed other apes lacked, although it has been shown that captive apes with ample access to food have levels of subcutaneous fat similar to humans. Additional features cited by Hardy include the location of the trachea in the throat rather than the nasal cavity, the human propensity for front-facing copulation, tears and eccrine sweating, though these claimed pieces of evidence have alternative evolutionary adaptationist explanations that do not invoke an aquatic context. Hardy additionally posited that bipedalism evolved first as an aid to wading before becoming the usual means of human locomotion, and tool use evolved out of the use of rocks to crack open shellfish. These last arguments were cited by later proponents of AAH as an inspiration for their research programs.

### Wading and bipedalism

AAH proponent Algis Kuliukas, performed experiments to measure the comparative energy used when lacking orthograde posture with using fully upright posture. Although it is harder to walk upright with bent knees on land, this difference gradually diminishes as the depth of water increases and is still practical in thigh-high water.

### Diving behavior and performance

Aside from working as a professor, Erika Schagatay is also an experienced scuba and freediver whose research centers around human diving abilities. She suggests that such abilities are consistent with selective pressure for underwater foraging during human evolution, and discussed other anatomical traits speculated as diving adaptations by Hardy/Morgan. John Langdon suggested that such traits could be enabled by a human developmental plasticity.

### Vernix caseosa

Tom Brenna, professor of pediatrics whose primary research focuses on fats, oils, and fatty acids, listened to the 2005 radio documentary *Scars of Evolution* where David Attenborough reported an observation that harbor seals were born with something that resembled human vernix caseosa. Intrigued, Brenna led a team that collaborated with Judy St Leger at San Diego Seaworld to compare the chemistry of human vernix and samples from California sea lion pups. They established that the molecular composition of both is similar, being rich in branched chain fatty acids and squalene.