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Aquatic ape hypothesis

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The aquatic ape hypothesis (or a common misnomer: aquatic ape theory) is the proposal that wading, swimming, and diving for food had a large evolutionary effect on the ancestors of humans and is in part responsible for the split between the common ancestors of humans and other great apes.

The hypothesis is in contradiction to the more established hypothesis that the environment of evolutionary adaptiveness for hominids was the savannas of the Rift ValleyWikipedia and the more recent hypotheses that the environment was forests or even that it rapidly fluctuated. The hypothesis is largely considered to be pseudoscience.


The hypothesis that the morphological divergence of hominids was dictated by an aquatic environment was first formulated in 1923 by the German physician Max WestenhöferWikipedia[1][2] and British marine biologist Sir Alister Hardy.Wikipedia[3] Hardy was inspired after returning from an Antarctic expedition where he noticed the subcutaneous blubber fat layers of whales and seals and saw parallels to humans.[4] He was also impressed by the human "exceptional ability" to swim. Fearing it would jeopardize his scientific career, Hardy did not publish his ideas until 1960.

Elaine Morgan (1920–2013) was a Welsh writer and the chief proponent of the aquatic ape hypothesis. Morgan took up the fight in 1972 when she discussed the aquatic ape hypothesis in her book The Descent of Woman.[5] Morgan was the primary proponent of the hypothesis, and culminated her argument in 1997 with the publication of The Aquatic Ape Hypothesis.[6][7] Her critics accused her of having used "sloppy and unscientific writing techniques" and maintain that she was guilty of quote mining.[8] She was described as being more of a popularizer of ideas than a real scientist. Regardless, she was awarded an honorary Doctor of Letters by Glamorgan University in December 2006.[9]

The hypothesis[edit]

The major divergence between the great apes and hominids can be placed somewhere between 5-7 million years ago (mya) based on the fossil record. During this time significant differences in anatomy developed including:

  • Bipedalism, which the theory claims was assisted by the supporting effects of water.[10]
  • Hairless skin, with the exception of the head which still needed to be shielded from the sun. Meanwhile primates such as baboons and vervet monkeys which live on the savanna have neither lost their hair nor developed an upright posture.[6]
  • Increased subcutaneous fat[11]
  • Greatly expanded brain size, which was promoted by the protein-rich fish diet.
  • A hooded nose, which prevents water from entering the nostrils.[12]
  • Greasy skin with an abundance of sebaceous glands, which can be interpreted as a waterproofing device.[13]
  • Expressive faces, since communicating through body language is difficult when wading in deep water or swimming but communicating through facial expression is still possible.[6]

Elaine Morgan, the primary proponent of this hypothesis, claimed that these traits are common in aquatic mammals. She claimed that these demonstrate convergent evolution of mammals living in an aquatic environment. The aquatic stage would have been about 5 mya until about 2.5 mya when the grassland expansion begun.

Objections to the hypothesis[edit]


There are several problems with this idea. The first is that convergent evolution predicts adaptations serving similar function, not necessarily similar structure. A platypus bill looks like a duck bill because it solves the precise same problem (sucking bugs out of mud); but the wings of a bat, a bird, and a bumblebee are products of convergent evolution in solving the problem of flight, but are structurally very different. Morgan's convergent evolution adaptations focus on structure.

The second problem is that evidence provided for the hypothesis is equally well accounted for by savanna-based adaptations without needing to posit an aquatic phase of human development.

  • Loss of body hair: lower parasite load and maintenance through sexual selection. Furthermore, many aquatic mammals have actually kept their body hair.[14] Several other savanna species have also lost much of their hair including elephants, rhinoceroses, and naked mole rats. Although both elephants[15] and rhinoceroses[16] are theorised to have evolved from aquatic ancestors so they may not be the best counter-examples—yet the only modern rhinoceros that spends much of its time in the water is the hairy rhinoceros.
  • Diet: the fatty acids for the brain were present in sufficient quantities on the savanna.
  • Diving reflex: terrestrial mammals show this too; there has been insufficient study of other apes to use this as evidence that humans are special in this regard.
  • Body fat: The quantities seen in present-day humans accord with those seen in domesticated mammals, i.e. we're quite well fed compared with wild dumb beasts.
  • Bipedalism: the hypothesis compares humans to quadrupeds, but we went from quadrupedal locomotion to brachiation; bipedalism follows quite readily from that.
  • Descended larynx: speech. The human larynx is not shaped like that of aquatic mammals, and descended larynxes are also seen in deer as well as other animals.[17]
  • Nose shape: again, speech. Speech was rather important in human development, oddly enough.
  • Sebaceous glands: not actually found in aquatic mammals. Appear to be sexually dimorphic (highly active in adolescent human males, scent receptors highly active in adolescent human females).
  • Swimming: humans really aren't that good at swimming. Dogs and cats do about as well.

A third major problem is there are actual characteristics indicative of aquatic mammals which humans notably lack. Aquatic mammals are testicond and have internal testes to insulate the gonads; humans are not testicond. Aquatic mammals also store large amounts of oxygen in the blood rather than the lungs, a trait also lacked by humans.

The Aquatic Ape Hypothesis cannot easily explain why these features were maintained after our ancestors supposedly left the water and moved to savannas. [18]

Furthermore, there's good evidence that many of the traits claimed to fall under the umbrella of the aquatic ape hypothesis evolved at radically different points in human evolutionary history. Fossils from 4.4 mya display bipedalism, while still possessing small brains long after, and not evolving sparse body hair until even later still.

One of the largest problems with the hypothesis is that since the 1960s, rather than improving and gathering evidence, the hypothesis has become more nebulous and vague. Rather than some specific aquatic phase, modern aquatic ape hypothesis supporters cite anything from fresh water millions of years ago, to salt water habitation more recently, to several different aquatic phases or even a general proximity to water to a greater degree than other apes. Incidentally, other apes and even some monkeys sometimes gather food from water and may stand bipedally to do this.[19][note 1]

There are also anti-science objections lodged against the creation of the hypothesis because Morgan had the idea first and then simply found differences between humans and other apes and composed ad hoc reasons associated with water. One could cherry pick data for many such pet theories without any merit behind them, whilst making them sound good on paper.


The aquatic ape hypothesis has mostly been ignored by palaeoanthropologists, and its strongest reception has been in popular literature and magazines. Very little research has been published in scientific journals directly supportive or critical of the hypothesis.[20] Morgan blamed the poor reception to the idea on people's perception of herself personally, since she had no advanced degree.

Supporters of the hypothesis claim that this lukewarm reception resulted from the fact that Elaine Morgan was not a member of the palaeoanthropological establishment. Detractors maintain that the lack of convincing evidence may have played a role.

Modern aquatic primates[edit]

Japanese macaques keeping warm in Jigokudani hot springs
  • Japanese macaque (Macaca fuscata) — since they live in a cold climate, during the winter, they frequent certain hot springs to keep warm.
  • Certain bonobos spend a certain amount of time in water, either in the shallows or crossing it.
  • Chimpanzees swim and walk bipedally in water.[21][22] Apparently the chimps use a kind of breaststroke.[23]
  • Orangutans have been known to spend time in water and swim.
  • Some monkeys in Thailand have also been filmed diving into water.[24] The Proboscis monkey loves swimming too.[25]

And, of course, Homo sapiens. Certain humans live in deserts etc, but some humans, especially those in the Indian Ocean islands, spend a lot of time in the sea, pearl diving, etc. Others are keen swimmers across distances of sea. While many humans are not currently "aquatic", a notable minority are.

See also[edit]

External links[edit]


  1. The last suggestion could make sense because evolving humans being more intelligent than other apes would better find ways of getting to food in any lake, river, stream, coastal environment where they happened to be. Perhaps there was no specific aquatic phase; instead there could have been evolving pre-humans/humans making use of water when there happened to be water-based resources in their area, but they remained able to manage in times of drought — after all, that is how modern humans behave. This in itself could perhaps have enabled us to evolve some limited adaptations to water. Theoretically there could have been a limited aquatic phase and the readiness of evolving hominids to use water opportunistically after this phase was sufficient to maintain some aquatic adaptations.


  1. About an Aquatic Stage in Man's Evolution with references to Max Westenhöfer and initial bipedalism
  2. Title page, excerpts from "Der Eigenweg des Menschen", 1942
  3. Cambridge University Press: The Aquatic Ape: Fact or Fiction?
  4. PDF: The New Scientist: Was Man More Aquatic in the Past? by Hardy, 1960
  5. Elaine Morgan, The Descent of Woman: The Classic Study of Evolution. Souvenir Press; Fourth Edition, 1 February 2001, ISBN 0285627007.
  6. 6.0 6.1 6.2 Elaine Morgan, The Aquatic Ape Hypothesis. Souvenir Press; Second Edition, 1 June 2017. ISBN 0285643614.
  7. Vaneechoutte, M. 2000. 'Report of the Symposium ‘Water and Human Evolution’. Human Evolution 15(3) 243-251.
  8. Critique of Morgan
  9. Glamorgan Honours Wales' Finest
  10. A Theory on the Evolution of the Habitual Orthograde Human Bipedalism — The "Amphibisce Generalistheorie": Niemitz, C
  11. Was man more aquatic in the past? (NewScientist): Hardy, A.
  12. Evidence for the unique function of docosahexanoic acid (DHA) during the evolution of the modern hominid brain (Lipids): Crawford, M et al
  13. Kingdon, Jonathan. (2003) Lowly Origin Princeton University Press, 242
  14. Pond, Caroline M. 1991 "Adipose Tissue in Human Evolution", pp. 193-220. The Aquatic Ape: Fact or Fiction? Edited by Machteld Roede, Jan Wind, John M. Patrick and Vernon Reynolds. Souvenir Press: London.
  15. aquatic elephant evolution
  16. aquatic rhinoceroses evolution
  17. W. T. Fitch and D. Reby, The descended larynx is not uniquely human. Proc Biol Sci. 2001 Aug 22;268(1477):1669-75. doi: 10.1098/rspb.2001.1704. PMID: 11506679; PMCID: PMC1088793.
  18. Why anthropologists don’t accept the Aquatic Ape Theory., 25 January 2005.
  19. Carsten Niemitz, The evolution of the upright posture and gait--a review and a new synthesis. Naturwissenschaften. 2010 Mar;97(3):241-63. doi: 10.1007/s00114-009-0637-3. Epub 2010 Feb 3. PMID: 20127307; PMCID: PMC2819487.
  20. Why don't anthropologists mention the AAT/H much?
  21. Marc Lallanilla, Who Knew? Apes Can Swim and Dive. Live Science, 20 August 2013.
  22. Swimming and diving behavior in apes. Stefano Di Criscio, YouTube.
  23. First documented report of swimming and diving in apes. Wits University via Science Daily, 4 August 2013.
  24. Cliff diving monkeys. TransumOrg, YouTube.
  25. Proboscis Monkey Swimming. MrSelamat Ethio, YouTube.