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The aquatic ape hypothesis (AAH), often also referred to as aquatic ape theory (AAT) and waterside hypotheses of human evolution, is the idea that the ancestors of modern humans were more aquatic in the past. 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 from life in the trees to hunt for food such as shell fish on the sea shore and that this explained many characteristics such as man's upright posture. It was not followed up except by Elaine Morgan, a script writer, who objected to the male image of the "mighty hunter" being presented in popular anthropological works by Raymond Dart, Desmond Morris and others. Whilst her 1972 book, The Descent of Woman was very popular with the public, it attracted no attention from scientists, who saw no way of testing assertions about soft body parts and human habits in the distant past.

Although Morgan removed the feminist polemic in several later books, so that it was discussed at a 1987 scientific conference and her 1990 book Scars of Evolution produced several favourable reviews in the scientific press, the thesis received scathing criticism from an anthropologist John Langdon in 1997 who argued that one hypothesis could not explain so many different phenomena. But another anthropologist Philip Tobias, discussing the role of water in human evolution, had declared in 1995 that the normal scientific explanation of human difference from the other apes, dubbed the savannah hypothesis, was disproved by discoveries about the Paleolithic climate in Africa.

In the last thirty years, one aspect of the hypothesis has received growing support within the scientific community: that at some point in the last five million years humans became dependent on aquatic food resources, including essential fatty acids and iodine, that are in short supply on the savannah and that this largely explains the enlargement of the human brain in this period. This is now supported by evidence of fish consumption by early humans up to two million years ago.

The idea remains controversial and is still less popular inside than outside the scientific community.

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 suggested this might have been during the Cretaceous, as he did not follow Charles Darwin in placing man among the apes. 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. As a young academic with a hypothesis belonging to a topic outside his field, and warned by colleagues that he could jeopardize his career if he published such a controversial idea, Hardy delayed reporting the hypothesis for some 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, shell fish, sea-urchins etc., in the shallow waters off the coast."

The idea received some interest after the article was published, notably from the geographer Carl Sauer, but was generally ignored by the scientific community thereafter. In 1967, the hypothesis was briefly mentioned in The Naked Ape, a popular book by the zoologist Desmond Morris, in which can be found the first use of the term "aquatic ape". But Hardy's promised full-scale study never appeared.

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 narrowed the focus exclusively to one activity, hunting, and this was taken up by the screenwriter Robert Ardrey in his 1961 best-seller African Genesis. Another screenwriter Elaine Morgan responded to this bloodthirsty vision 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 sea shore. She took her lead from a section in Desmond Morris's 1967 book The Naked Ape 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 interest in the academic community, she dropped the feminist polemic and wrote a series of books–The Aquatic Ape (1982), The Scars of Evolution (1990), The Descent of the Child (1994) and The Aquatic Ape Hypothesis (1997)–which explored the issues in more detail.

The Hardy/Morgan hypothesis

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.

Morgan's most recent summary of the thesis was in 2011:

Waterside hypotheses of human evolution assert that selection from wading, swimming and diving and procurement of food from aquatic habitats have significantly affected the evolution of the lineage leading to Homo sapiens as distinct from that leading to Pan.

Neither Hardy or Morgan ever envisaged a stage where humans lived at sea, although this quickly became part of the public perception. Also the time period for this dependence has changed significantly over the last 50 years in line with anthropological thought.

The possible consequences of Hardy's hypothesis, discussed by Hardy and Morgan, include:

• Bipedalism: Hardy stated:

It seems to me likely that Man learnt to stand erect first in water and then, as his balance improved, he found he became better equipped for standing up on the shore when he came out, and indeed also for running.

• Loss of body hair: Hardy pointed out that "the loss of hair is characteristic of a number of aquatic mammals, for example, the whales, the Sirenia and the hippopotamus", though he pointed out that the hairs were still there, though so reduced in thickness that they were almost invisible. When swimming in the sun, only the head still needs protection. Morgan compares this with seven other theories for hairlessness starting with parasites.
• Subcutaneous fat: unlike other primates, humans have an extended fat layer, that is seen more markedly in whales and other sea mammals. This was Hardy's original spur to forming the theory, quoting a 1929 book: "The peculiar relation of the skin to the underlying superficial facia is a very real distinction, familiar enough to everyone who has repeatedly skinned both human subjects and any other member of the Primates." Hardy also notes that this contributes to human ability to cope with varying air temperature, which adds to their widespread distribution in different habitats.
• Speech: Humans together with aquatic mammals depend less on smell and touch as means of communication than vocalisation. By the 1980s Morgan focused on the human larynx, which is situated in the throat rather than the nasal cavity, a feature that is shared by some aquatic animals who use it to close off the trachea while diving; it also facilitates taking large breaths of air upon surfacing.
• Eccrine sweating and Tears: Human sweat using a different type of gland than other primates, which predominately use panting for cooling as sweating is wasteful of water for an animal on the savannah, although baboons and patas monkeys (which feed on fruit) do supplement this by sweating. Humans, alone among primates, cry. Tears are often observed in sea birds to get rid of excess salt.
• Sex: Human sexual activity varies in several ways from other primates. Copulation is typically frontal, which is observed in aquatic mammals and manatees, but not apes. This front entry probably causes the loss of orgasm in the female.

Human infants can control their breath without instruction

• Swimming: humans share with aquatic mammals the diving reflex by which the heart slows down when under water reducing the need for oxygen.
• Fat babies: Human babies have far more fat, acquired in the latter stages of pregnancy. This helps in swimming which they can do naturally if exposed early enough, and birthing in water is a possibility that has only recently been rediscovered.
• Tool use: Hardy suggested that Man learnt his tool-making on the shore by using stones to crack open shell-fish, pointing to the middens of mesolithic remains.

Reactions

Popular reaction

Alister Hardy was astonished and mortified in 1960 when the national Sunday papers carried banner headlines "Oxford professor says man a sea ape", causing problems with his Oxford colleagues. As he later said to his ex-pupil Desmond Morris, "Of course I then had to write an article to refute this saying no this is just a guess, a rough hypothesis, this isn't a proven fact. And of course we're not related to dolphins."

Elaine Morgan's book Descent of Woman became an international best-seller, a Book of the Month selection in the United States and was translated into ten languages. Part of this was related to the growing women's liberation movement and she assumed that the total lack of response to her book from the academic community was due to this. "The response I had not foreseen was total silence. But in respect of the aquatic theme that is what I got from them - and with few exceptions still get. That kind of silence is a virtually unbeatable strategy". So she took out the polemics and rewrote the scientific part publishing it as The Aquatic Ape ten years later with the same results from academia, but with continued support from the public.

Academic reaction

From anthropologists

The AAH has received little attention from mainstream paleoanthropologists; it is not accepted as empirically supported by the scholarly community, and has been met with significant skepticism. Some reviewers seem surprised that Morgan had not published in peer reviewed publications.

One conference has been held in Valkenburg, Netherlands in 1987. Its 22 participants included academic proponents and opponents of the theory and several neutral observers headed by the anthropologist Vernon Reynolds of Oxford University. His summary at the end was:

Overall, it will be clear that I do not think it would be correct to designate our early hominid ancestors as 'aquatic'. But at the same time there does seem to be evidence that not only did they take to water from time to time but that the water (and by this I mean inland lakes and rivers) was a habitat that provided enough extra food to count as an agency for selection.

In a widely read 1997 critique, Langdon considered the AAH under the heading of an "umbrella hypothesis" and pointed to the difficulty of ever disproving such a thesis, however popular it was with the public. He suggested that some anthropologists had regarded the ideas as not worth the trouble of a rebuttal. In addition, the AAH mostly concerned developments in soft tissue anatomy and physiology, whilst paleoanthropologists rarely speculated 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.

Langdon objected to Morgan's opposition to the "savannah hypothesis" which he took to be the "collective discipline of paleoanthropology". In 1995, the notable paleoanthropologist Philip Tobias had declared that the savannah hypothesis was dead, because the open conditions did not exist when humanity's precursors stood upright and that therefore the conclusions of the Valkenberg conference were no longer valid. Tobias praised Morgan's book Scars of Evolution as a "remarkable book" though he said that he did not agree with all of it. Bender and Tobias further criticised the idea by pointing out that the coming out of the forest of man's precursors had been an unexamined assumption of evolution since the days of Lamarck, and followed by Darwin, Wallace and Haeckel, well before Dart used it.

Popular support for the AAH has become an embarrassment to some anthropologists who want to explore the effects of water on human evolution without engaging with the AAH, which they consider "emphasizes adaptations to deep water (or at least underwater) conditions". Foley and Lahr suggest that "to flirt with anything watery in paleoanthropology can be misinterpreted", but argue "there is little doubt that throughout our evolution we have made extensive use of terrestrial habitats adjacent to fresh water, since we are, like many other terrestrial mammals, a heavily water-dependent species." But they allege that "under pressure from the mainstream, AAH supporters tended to flee from the core arguments of Hardy and Morgan towards a more generalized emphasis on fishy things."

In a recent book, the Nature editor Henry Gee, whilst admitting the significance of a seafood diet for the development of the brain, 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".

From biologists and physicians

The reaction from biologists was noticeably different from that of the anthropologists, as they used it to generate a number of hypotheses of their own. A 1980 review article in Medical Hypotheses by Stephen Cunnane, a Canadian nutritionist, was followed by papers by Marc Verhaegen, a Belgian doctor, exploring possible links with disease, and one from an ENT specialist in London discussing the exostoses found in the ears of swimmers. But the substantial contribution at this point was by the director of the Institute of Brain Chemistry in London, Michael Crawford, in his 1989 book The Driving Force. This explored the contribution of nutrition to human evolution, and in particular the importance of Omega-3 fatty acids for the development of the brain. "A branch of the line of primitive ancestral apes was forced by competition to leave the trees and feed on the seashore. Searching for oysters, mussels, crabs, crayfish and so on they would have spent much of their time in the water and an upright position would have come naturally." He thus drew attention particularly to the balance of Omega-3 fatty acids derived from algae and plankton on the seashore and Omega-6 acids derived from land seeds which is characteristic of brains, as well as trace elements such as iodine.

Awareness of the possibilities in the medical community led to positive reviews of Scars of Evolution in the British Medical Journal as well as one in Nature.

From philosophers

Daniel Dennett challenged both Elaine Morgan and the scientific establishment in his book "Darwin's Dangerous Idea": He first commented "During the last few years, when I have found myself in the company of distinguished biologists, evolutionary theorists, paleoanthropologists and other experts, I have often asked them to tell me, please, exactly why Elaine Morgan must be wrong about the aquatic theory. I haven’t yet had a reply worth mentioning, aside from those who admit, with a twinkle in their eyes, that they have also wondered the same thing." He followed this up by pointing out that the tales of the establishment, the so-called savannah hypothesis, are no better confirmed than those of Morgan: "What they mainly have going for them, so far as I can see, is that they occupied the high ground in the textbooks before Hardy and Morgan tried to dislodge them. Both sides are indulging in adaptionist Just So stories and since some story or other must be true, we must not conclude we have found the story just because we have come up with a story that seems to fit the facts. To the extent that adaptionists have been less than energetic in seeking further confirmation (or dreaded disconfirmation) of their stories, this is certainly an excess that deserves criticism."

Waterside research on human evolution

In the last twenty years, scientific research on the subject has begun to emerge with the emphasis on the possible exploitation of resources near rivers and lakes as well as the sea coasts. It has also drawn attention to the rapid dispersal of early humans throughout the world on coasts and rivers. This section only covers issues where efforts have been made to test hypotheses. Many of the 'soft tissue' issues have not been explored in this way.

Wading hypotheses of bipedalism

Despite a large number of theories, the reason for human bipedalism has remained elusive. Observation shows that most primates will naturally walk on two feet when wading in deeper water. The water helps them to keep their balance and repeated experience would slowly get over the "bent-knees" handicap. After reviewing 30 different explanations of bipedalism, Niemitz proposes a shore dweller hypothesis of wading, though distancing himself from the AAH. In a multi-factored evaluation, Kuliukas found various wading scenarios at the top of some 40 other models, favouring a river context over coastal. Observations of captive bonobos showed that in waist deep water they are always observed to switch to bipedalism, with similar observations for other apes. He also reports experiments on wading efficiency in various depths of water with knee-bent hips. Darwin's original suggestion that the function of an upright posture was to free the hands for various purposes was discredited when it was shown that bipedalism, some 4-5m years ago, preceded the growth in brain size. Running upright isn't more effective than on all-fours, and walking only becomes efficient when the body is fully straightened. An upright posture is widely assumed to be connected with food procurement, but climbing, in an arboreal habitat, hasn't produced the same effects in other primates and a combination of wading and diving (e.g. reaching for mussels on the bottom) is a more convincing scenario. Aquatic foraging provides a powerful incentive for wading, as does cooling down in an equatorial climate. It would also apply to both sexes, unlike the various hunting hypotheses. A comparative analysis of the shape of the australopithecine pelvis indicates that the species walked upright but with a gait comprising more side-to-side motion than modern human walking, compatible with significant wading.

Fish consumption and brain size

Neanderthal skull (right) compared with modern human

One of the major changes in human biology has been the growth in size of the brain from around 350ml (Ardipithecus) to 1,600ml (Neanderthal) which took place between approximately 4.4m and 0.4m years ago before settling down to 1,300ml in modern humans. Traditionally this has been explained by the increasing meat consumption by hominins (or even a fruit diet to explain reducing teeth), but the same effect was not observed in carnivores on the savannah whose encephalization quotient remained low. The reason is that brain development is essentially dependent on the polysunsaturated fats AA and DHA (or their precursors) which occur in roughly equal proportions, as well as trace elements such as iodine. These are plentiful in the marine environment, where brains originally developed, but are lacking in inland areas (particularly DHA). A series of papers and books have explained these issues and pointed to the availability of rich sources of DHA in catfish and shellfish which were available in the Rift Valley environments such as Lake Turkana. These would be available without the use of tools, apart from wave-rounded stones (which were plentiful along the water's edge) for smashing the shells and led eventually to cave dwelling by the waterside which became the hallmark of early humans. When successive waves of homo left Africa, they followed the coastlines into Europe and Asia, which provided sources of fresh water as well as the benefits of the beachcomber. Dry season access to aquatic habitats was also a necessary condition for adaption to savanna habitats.

What has been lacking has been the paleontological evidence that early humans consumed fish in significant amounts earlier than 40,000 years ago. Part of the problem has been the avoidance of taphonomic bias by researchers: most fossils occur in lacustrine environments and the presence of fish remains is therefore no proof of fish consumption. Fish bones often decompose so that special tests are required to detect them. Also the archaeological record of human fishing and coastal settlement is fundamentally flawed due to postglacial sea level rise. But since the year 2000, this evidence is being steadily uncovered: in East Timor, evidence of deep sea fishing with hooks 42,000 years ago; in Europe the date of the first consumption of fish has been increased to 115,000 and then 250,000 years ago; and in South Africa a coastal colony of anatomically modern humans was crucially dependent on seafood 160,000 years ago. In 2015, a fresh examination of remains collected by Dubois in 1891 during the discovery of homo erectus in Java demonstrated that they consumed freshwater shellfish around half a million years ago, finding also shellfish tools and the earliest human engraving so far discovered. Microscopic analysis of fish food remains extending back to 2m years from the Olduvai gorge has now shown cut marks indicating butchery.

Humans have returned to the norm of brain size seen in small and aquatic mammals whereas other primates and carnivores steadily lost relative brain capacity (though the relationship between brain size and intelligence is more complex). Problems in landlocked communities have been observed ever since, with reports of cretinism in the Alps since the 18th century and widespread goitres in parts of Africa, which is only prevented by the addition of iodine and vitamin A to diets.

Auditory exostosis

A narrowing of the ear canal due to bony growths protruding into the ear is caused by regular exposure to cold water. It is sometimes known as surfer's ear. Auditory exostoses have been seen in fossils of Homo erectus and Neanderthals, which demonstrates frequent swimming, according to the ENT specialist Peter Rhys-Evans. The idea that there is a genetic component has been discredited. A book by G. P. Rightmire reported exotoses in the skulls of Homo erectus, including one from the Lake Ndutu in the Olduvia Gorge. Evidence also has been found in Brazil dating back 5,000 years. This provides evidence that extensive swimming has been a characteristic of many human communities for longer than had been imagined.

Vernix Caseosa

One of the tests of a scientific theory is that it makes predictions that can be fulfilled. Morgan in Descent of the Child drew attention to Vernix caseosa, the cheesy varnish that covers most human babies at birth and was thought to be unique to humans, and suggested that it was a sign of our semi-aquatic past. In 2005, in a radio series called The Scars of Evolution, David Attenborough recounted a search to see whether any other aquatic mammals showed the same phenomenon. He reported that a Canadian researcher Don Bowen had observed this phenomenon in harbour seals. In a second radio series in 2016, The Waterside Ape, Attenborough included a report from Prof. Tom Brenna of Cornell University that an analysis of vernix from California sea lions had shown that it was composed of the same fatty acids as are found in that of humans. The function is to deliver fatty acids to the fetal gut.

The discovery that several aquatic mammals show signs that were thought to be uniquely human supports a waterside hypothesis.

See also

• Endurance running hypothesis
• Hunting hypothesis
• Savanna theory

Bibliography

• Crawford, Michael; Marsh, David (1989). The Driving Force. London: Heinemann.
• Cunnane, Stephen; Stewart, Kathlyn, eds. (2010). Human Brain Evolution: The Influence of Freshwater and Marine Food Resources. Wiley. ISBN 9780470609873.
• Hardy, A (1960). "Was man more aquatic in the past?" (PDF). New Scientist. 7: 642–645. Archived from the original (PDF) on 26 March 2009.. More legible version at PDF
• Langdon, JH (1997). "Umbrella hypotheses and parsimony in human evolution: a critique of the Aquatic Ape Hypothesis". J. Hum. Evol. 33 (4): 479–94. doi:10.1006/jhev.1997.0146. PMID 9361254.
• Morgan, E (1972). The Descent of Woman. London: Souvenir Press. ISBN 9780285639843.
• Morgan, E (1982). The Aquatic Ape. London: Souvenir Press.
• Morgan, E (1990). The Scars of Evolution. London: Souvenir Press. ISBN 9780195094312.
• Morgan, E (1994). The Descent of the Child. London: Souvenir Press.
• Morgan, E (1997). The Aquatic Ape Hypothesis. London: Souvenir Press. ISBN 9780285639812.
• Morgan, E (2008). The Naked Darwinist. London: Souvenir Press. ISBN 9780952562030.
• Roede, Machteld (1991). Aquatic Ape: Fact or Fiction: Proceedings from the Valkenburg Conference. Souvenir Press. ISBN 0-285-63033-4.
• Vaneechoutte, M; Kuliukas, A V; Verhaegen, M (2011). Was Man More Aquatic In The Past? Fifty Years After Alister Hardy - Waterside Hypotheses Of Human Evolution. Bentham Science Publishers. ISBN 978-1-60805-244-8.

Category:Biological hypotheses Category:Human evolution Category:Aquatic mammals