The aquatic ape hypothesis (AAH), also referred to as aquatic ape theory (AAT) or the waterside hypothesis of human evolution, postulates that the ancestors of modern humans took a divergent evolutionary pathway from the other great apes by becoming adapted to a more aquatic habitat. While the hypothesis has some popularity with the lay public, it is generally ignored or classified as pseudoscience by anthropologists.
The theory developed before major discoveries of ancient hominin fossils in East Africa. The hypothesis was initially proposed by the English 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 coast and seabed, leading to adaptations that explained distinctive characteristics of modern humans such as functional hairlessness and bipedalism. The popular science writer Elaine Morgan supported this hypothesis in her 1972 book The Descent of Woman. In it, she contrasted the theory with zoologist and ethologist Desmond Morris's theories of sexuality, which she believed to be rooted in sexism.
Anthropologists do not take the hypothesis seriously: John Langdon characterized it as an "umbrella hypothesis" (a hypothesis that tries to explain many separate traits of humans as a result of a single adaptive pressure) that was not consistent with the fossil record, and said that its claim that it was simpler and therefore more likely to be true than traditional explanations of human evolution was not true. According to anthropologist John Hawkes, the AAH is not consistent with the fossil record. Traits that the hypothesis tries to explain evolved at vastly different times, and distributions of soft tissue the hypothesis alleges are unique to humans are common among other primates.
History In 1942 the German pathologist Max Westenhöfer (1871–1957) discussed 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. As he did not believe human beings were apes, he believed this might have been during the Cretaceous, contrary to what is possible given the geologic and evolutionary biology evidence available at the time. 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." He later abandoned the concept.
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, although his work, unlike Westenhöfer's, was rooted in the Darwinian consensus. 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 finally voiced his thoughts in a speech to the British Sub-Aqua Club in Brighton on 5 March 1960. Several national newspapers reported sensational presentations of Hardy's ideas, which he countered by explaining them more fully in an article in New Scientist on 17 March 1960: "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, shellfish, sea-urchins etc., in the shallow waters off the coast."
The idea was generally ignored by the scientific community after the article was published. Some interest was received, notably from the geographer Carl Sauer whose views on the role of the seashore in human evolution "stimulated tremendous progress in the study of coastal and aquatic adaptations" inside marine archaeology. In 1967, the hypothesis was mentioned in The Naked Ape, a popular book by the zoologist Desmond Morris, who reduced Hardy's phrase "more aquatic ape-like ancestors" to the bare "aquatic ape", commenting that "despite its most appealing indirect evidence, the aquatic theory lacks solid support".
While traditional descriptions of 'savage' existence identified three common sources of sustenance: gathering of fruit and nuts, fishing, and hunting, in the 1950s, the anthropologist Raymond Dart focused on hunting and gathering as the likely organizing concept of human society in prehistory, and hunting was the focus of the screenwriter Robert Ardrey's 1961 best-seller African Genesis. Another screenwriter, Elaine Morgan, responded to this focus in her 1972 Descent of Woman, which parodied the conventional picture of "the Tarzanlike figure of the prehominid who came down from the trees, saw a grassland teeming with game, picked up a weapon and became a Mighty Hunter," and pictured a more peaceful scene of humans by the seashore. She took her lead from a section in Morris's 1967 book which referred to the possibility of an Aquatic Ape period in evolution, his name for the speculation by the biologist Alister Hardy in 1960. When it aroused no reaction in the academic community, she dropped the feminist criticism and wrote a series of books–The Aquatic Ape (1982), The Scars of Evolution (1990), The Descent of the Child (1994), The Aquatic Ape Hypothesis (1997) and The Naked Darwinist (2008)–which explored the issues in more detail. Books published on the topic since then have avoided the contentious term aquatic and used waterside instead.
The Hardy/Morgan hypothesis Hardy's hypothesis as outlined in New Scientist was:
Hardy argued a number of features of modern humans are characteristic of aquatic adaptations. He pointed to humans' lack of body hair as being analogous to the same lack seen in whales and hippopotamuses, 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.
The diving reflex is sometimes cited as evidence. This is exhibited strongly in aquatic mammals, such as seals, otters and dolphins. It also exists as a lesser response in other animals, including human babies up to 6 months old (see infant swimming). However adult humans generally exhibit a mild response.
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.
Morgan summed up her take on the hypothesis in 2011:
Reactions
The AAH is generally ignored by anthropologists, although it has a following outside academia and conferences on the topic have received celebrity endorsement, for example from David Attenborough. Despite being debunked, it returns periodically, being promoted as recently as 2019.
Academics who have commented on the aquatic ape hypothesis include categorical opponents (generally members of the community of academic anthropology) who reject almost all of the claims related to the hypothesis. Other academics have argued that the rejection of Hardy and Morgan is partially unfair given that other explanations which suffer from similar problems are not so strongly opposed. A conference devoted to the subject was held at Valkenburg, Netherlands, in 1987. Its 22 participants included academic proponents and opponents of the hypothesis and several neutral observers headed by the anthropologist Vernon Reynolds of the University of Oxford. His summary at the end was:
Critiques The AAH is considered to be a classic example of pseudoscience among the scholarly community, and has been met with significant skepticism. The Nature editor and paleontologist Henry Gee has argued that the hypothesis has equivalent merit to creationism, and should be similarly dismissed.
In a 1997 critique, anthropologist John Langdon considered the AAH under the heading of an "umbrella hypothesis" and argued that the difficulty of ever disproving such a thing meant that although the idea has the appearance of being a parsimonious explanation, it actually was no more powerful an explanation than the null hypothesis that human evolution is not particularly guided by interaction with bodies of water. Langdon argued that however popular the idea was with the public, the "umbrella" nature of the idea means that it cannot serve as a proper scientific hypothesis. Langdon also objected to Morgan's blanket opposition to the "savannah hypothesis" which he took to be the "collective discipline of paleoanthropology". He observed that some anthropologists had regarded the idea as not worth the trouble of a rebuttal. In addition, the evidence cited by AAH proponents mostly concerned developments in soft tissue anatomy and physiology, whilst paleoanthropologists rarely speculated on evolutionary development of anatomy beyond the musculoskeletal system and brain size as revealed in fossils. After a brief description of the issues under 26 different headings, he produced a summary critique of these with mainly negative judgments. His main conclusion was that the AAH was unlikely ever to be disproved on the basis of comparative anatomy, and that the one body of data that could potentially disprove it was the fossil record.
In a blog post originally published in 2005 and continually updated since, anthropologist John D. Hawks said that anthropologists don't accept the AAH for several reasons. Hardy and Morgan situated the alleged aquatic period of human nature in a period of the fossil record that is now known not to contain any aquatic ancestors. The traits the AAH tries to explain actually evolved at wildly different time periods. The AAH claims that the alleged aquatic nature of humanity is responsible for human patterns of hair, fat, and sweat, but actually all of these things are similar in humans to other primates. To the extent they are exceptional in any primate relative to other primates, or in primates relative to other mammals, they are exceptional for well-understood thermodynamic reasons.
Palaeontologist Riley Black concurred with the pseudoscience label, and described the AAH as a "classic case of picking evidence that fits a preconceived conclusion and ignoring everything else". Physical anthropologist Eugenie Scott has described the aquatic ape hypothesis as an instance of "crank anthropology" akin to other pseudoscientific ideas in anthropology such as alien-human interbreeding and Bigfoot.
In The Accidental Species: Misunderstandings of Human Evolution (2013), Henry Gee remarked on how a seafood diet can aid in the development of the human brain. He nevertheless criticized the AAH because "it's always a problem identifying features [such as body fat and hairlessness] that humans have now and inferring that they must have had some adaptive value in the past." Also "it's notoriously hard to infer habits [such as swimming] from anatomical structures".