Aquatic ape hypothesis

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. 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 even 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. 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 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.

Hardy's hypothesis bears on some of the following topics:

Bipedalism: Hardy stated:

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.

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.

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.

Popular

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 1972 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.

From scientists

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, at 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 thing, however popular it was with the public. He observed that some anthropologists had regarded the idea 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. Anatomy lecturer Bruce Charlton gave Morgan's book Scars of Evolution an enthusiastic review in the British Medical Journal in 1991, calling it "exceptionally well written" and "a good piece of science".

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."

Anthropologist John D. Hawks has written that it is fair to categorize the AAH as pseudoscience because of social factors that inform it, particularly the personality-led nature of the hypothesis and the unscientific approach of its adherents.

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 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".

Books written by others

In their 1989 book The Driving Force: Food, Evolution and The Future, biologists Michael Crawford and David Marsh explored the contribution of nutrition to human evolution, and in particular claimed that Omega-3 fatty acids were vital 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." Reviewing the book for the New Scientist, biologists Caroline Pond and Dick Colby were highly critical, saying that the work provided "no significant new information that would be of interest to biologists" and that its style was "speculative, theoretical and in many places so imprecise as to be misleading."

Efforts made to test hypotheses

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 and bipedalism

After reviewing 30 different explanations of bipedalism, Niemitz proposed 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. He noted that captive bonobos always switch to bipedalism in waist deep water, as do other apes, and reported 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. Walking becomes efficient when the body is fully straightened. An upright posture is widely assumed to be connected with food procurement. Aquatic foraging happens in the context wading and wading cools animals in a hot equatorial climate. A comparative analysis of the shape of the australopithecine pelvis indicates that the species walked upright but with more side-to-side motion than modern human walking.

Nutrients and brain size

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. Increasing meat consumption by hominins (or even a fruit diet to explain reducing teeth) is associated with this growth, but the same effect was not observed in carnivores on the savannah whose encephalization quotient remained low. Brain development is dependent on the polyunsaturated 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 but are lacking in some 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 resources 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 hominin fossils occur in marginal 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.

According to the director of the Institute of Brain Chemistry and Human Nutrition at Imperial College, London, "the evolution of a large brain on the savannahs of Africa was impossible. The only way it could have happened was with the resources of the marine food-web which initiated the growth and development of the brain in the first place". Crawford and Marsh argue that the norm of brain size seen in small and aquatic mammals is similar to humans and they further opine that other primates and carnivores had lost relative brain capacity (though the relationship between brain size and intelligence is not isomorphic). Problems in landlocked communities have been observed 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 to diets. "Without the availability of iodized table salt, non-coastal (inland) habitats do not provide foods rich enough to meet human iodine requirements."

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

Morgan's Descent of the Child mentions the vernix caseosa, the cheesy varnish that covers most human babies at birth. This was thought to be unique to humans, and Morgan suggested that it was a sign of our semi-aquatic past. In 2005, in a radio series called The Scars of Evolution, David Attenborough described a search to see whether any other aquatic mammals showed the same phenomenon. He reported that the 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 Tom Brenna of Cornell University that vernix from California sea lions 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 was claimed by Attenborough to support a waterside hypothesis.