Aquatic ape hypothesis

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The aquatic ape hypothesis (AAH), sometimes referred to as the aquatic ape theory, asserts that wading, swimming and diving for food exerted a strong evolutionary effect on the ancestors of the genus Homo, and that this is in part responsible for the split between the common ancestors of humans and other great apes. The AAH attempts to explain the large number of physical differences between humans and other apes in terms of the environment, methods of feeding and types of food of early hominids living in coastal and river regions.

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[edit] Hypotheses

As compared to the great apes, their nearest living relatives, humans exhibit many significant differences in anatomy and physiology, including bipedalism,[1] almost hairless skin like some marine mammals,[2] hair growth patterns following water flow-lines,[3] increased subcutaneous fat for insulation,[4][5] descended larynx,[3][6] vernix caseosa,[3] a hooded nose and the philtrum preventing water from entering the nostrils [3], voluntary breath control like marine mammals and birds,[3][7] and greasy skin with an abundance of sebaceous glands, which can be interpreted as a waterproofing device.[8] It has also been suggested that the abundance of docosahexaenoic acid in seafood would have been helpful in the development of a large brain.[9]

There are several variants on the broad theme that early or proto-humans lived in close proximity to water, gathering much of their food in or near shallow bodies of water and developing and adapting new modes of locomotion in order to move and gather food (possibly including wading,[1] swimming,[10] and diving[4]). Proponents have disagreed on the relative importance of fresh water[11] versus coastal salt- or brackish-water[12] habitats. Although the earliest proponents argued for an early (Miocene, about 6 million years ago) timescale,[4] most now favour the view that the critical period of close association with waterside habitats was much later, Pleistocene or possibly late Pliocene (i.e., less than 2 million years ago).[13][14] Possibly it happened when our ancestral Homo population spread along the South Asian coasts (so-called Out of Africa 1) where during the Ice Ages the lowered sea levels exposed large areas of the continental shelves; shell and crayfish were easily procurable by a dextrous, tool-using, thick-enameled, omnivorous primate and contained poly-unsaturated fatty acids such as DHA that were essential to brain growth. This may explain why this seaside phase (100-120 metres below sea level now) did not leave many traces in the fossil and archaeological record. From the coasts their descendants might have trekked into the continents along lakes and rivers.[15]

[edit] History

Sometime prior to 546 BC, the Milesian philosopher Anaximander proposed that mankind had sprung from an aquatic species of animal. He thought that the extended infancy of humans could not have originally permitted survival as a land-based species. This idea was based on elemental forces of mutation rather than natural selection.

The German biologist Max Westenhöfer was perhaps the first to publish the idea in an evolutionary context, writing in 1942 that "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."[16]

The similarity of the subcutaneous fat in aquatic birds and larger aquatic mammals to the fat in humans had already been noticed by marine biologist, Sir Alister Hardy in 1930, while reading Frederic Wood Jones' Man's Place among the Mammals, which included the question of why humans, unlike all other land mammals, had fat attached to their skin. Hardy realised that this trait sounded like the blubber of marine mammals, and began to suspect that humans had ancestors more aquatic than previously imagined. Because it was outside his field and aware of the controversy it would cause, Hardy delayed reporting his theory. After he had become a respected academic, Hardy finally voiced his thoughts in a speech to the British Sub-Aqua Club in Brighton on 5 March 1960.

News of Hardy's speech generated immediate controversy in the field of paleoanthropology, and Hardy followed up by publishing two articles in the scientific magazine New Scientist[4]. In the article of 17 March 1960[17] Hardy defined his idea: "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 1960:642) Despite receiving some positive feedback in the Letters pages of New Scientist in the weeks that followed, and strong backing from a professor of geography,[18] the idea was largely ignored by the scientific community.

In 1967, the hypothesis was positively reviewed in The Naked Ape, a book by Desmond Morris in which can be found the first use of the term "aquatic ape" (Morris 1967:29).[19] Writer Elaine Morgan read about the idea in Morris' book and was struck by its potential explanatory power. She developed and promoted it over the next thirty years, publishing six books on the subject.[20][2][21][22][23][24] Several other proponents have published work in favour of the aquatic ape hypothesis during this time including the physician Marc Verhaegen,[13] neurochemists Michael Crawford[9] and Stephen Cunnane,[12] and ecologist Derek Ellis.[11]

[edit] Academic reception

The hypothesis and its variations have been largely ignored by mainstream paleoanthropology, although occasional papers have criticised certain aspects of it.[25][26][27][28][29] It has been suggested, for example, that because a broad terrestrial diet would ensure sufficient access to docosahexaenoic acid, there was no requirement for high consumption of seafood and accordingly no reason to posit an aquatic phase in human evolution for dietary reasons.[30]

In 1991 a symposium was held in Valkenburg, Holland, titled "Aquatic Ape: Fact or fiction?", which published its proceedings.[31] The chief editor, Vernon Reynolds, rejected the strong version of the hypothesis, but accepted a weaker form, summarizing that "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 the 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. As a result, we humans today have the ability to learn to swim without too much difficulty, to dive, and to enjoy occasional recourse to the water."[32]

Despite the conciliatory wording of the summary, and the fact that half of the submitted papers were in favour of the hypothesis, it was reported in the anthropological press that the hypothesis had been rejected.[27]

However there has since been some acceptance. In 2004 Colin Groves, Professor of Biological Anthropology at the Australian National University in Canberra, Australia with co-author David W. Cameron stated that

...nor can we exclude the Aquatic Ape Hypothesis (AAH). Elaine Morgan has long argued that many aspects of human anatomy are best explained as a legacy of a semiaquatic phase in the proto-human trajectory, and this includes upright posture to cope with increased water depth as our ancestors foraged farther and further from the lake or seashore. At first, this idea was simply ignored as grotesque, and perhaps as unworthy of discussion because proposed by an amateur. But Morgan's latest arguments have reached a sophistication that simply demands to be taken seriously (Morgan 1990, 1997). And although the authors shy away from more speculative reconstructions in favour of phylogenetic scenarios, we insist that the AAH take its place in the battery of possible functional scenarios for hominin divergence.[33]

[edit] See also

Evolutionary biology portal

[edit] References

  1. ^ a b Niemitz, C (2002). "A Theory on the Evolution of the Habitual Orthograde Human Bipedalism - The "Amphibisce Generalistheorie"". Anthropologischer Anzeiger 60: 3–66. 
  2. ^ a b Morgan, Elaine (1982). The Aquatic Ape. Stein & Day Pub. ISBN 0-285-62509-8. 
  3. ^ a b c d e Morgan, Elaine (1997). The Aquatic Ape Hypothesis. Souvenir Press. ISBN 0-285-63518-2. 
  4. ^ a b c d Hardy, A. (1960). "Was man more aquatic in the past". New Scientist 7: 642–645. 
  5. ^ Pawlowski, Boguslaw (1998). "Why are human newborns so big and fat?". Human Evolution 13: N1. 
  6. ^ Crelin, Edmund S (1987). The Human Vocal Tract: Anatomy, Function, Development, and Evolution. New York: Vantage Press. ISBN 0 533 06967 X. 
  7. ^ Jim Moore's "AAT Sink or Swim?" Web Site - Accessed 29 Oct 2008
  8. ^ Kingdon, Jonathan. (2003) Lowly Origin Princeton University Press, 242
  9. ^ a b Crawford, M et al (2000). "Evidence for the unique function of docosahexanoic acid (DHA) during the evolution of the modern hominid brain". Lipids 34: S39–S47. 
  10. ^ Patrick, John (1991). Human Respiratory Adaptations for Swimming and Diving. Souvenir Press. ISBN 0-285-63033 4. 
  11. ^ a b Ellis DV (1993). "Wetlands or aquatic ape? Availability of food resources". Nutrition and health 9 (3): 205–17. PMID 8183488. 
  12. ^ a b Cunnane SC, Plourde M, Stewart K, Crawford MA (2007). "Docosahexaenoic acid and shore-based diets in hominin encephalization: a rebuttal". Am. J. Hum. Biol. 19 (4): 578–81. doi:10.1002/ajhb.20673. PMID 17546620. 
  13. ^ a b Verhaegen, M.; Puech, P.F.; Munro, S. (2002). "Aquarboreal ancestors?" (pdf). Trends in Ecology & Evolution 17 (5): 212–217. doi:10.1016/S0169-5347(02)02490-4. http://allserv.rug.ac.be/~mvaneech/OP%20Verhaegen%20final%20styled.doc.pdf. Retrieved on 2007-10-29. 
  14. ^ Verhaegen M, Munro S, Vaneechoutte M, Bender R, Oser N (2007). "The original econiche of the genus Homo: Open Plain or Waterside?". SI Muñoz ed. Ecology Research Progress. Nova NY http://users.ugent.be/%7Emvaneech/Verhaegen%20et%20al.%202007.%20Econiche%20of%20Homo.pdf: 155–186. 
  15. ^ Verhaegen M & Munro S (2002). "The continental shelf hypothesis". Nutrition & Health 16: 25–28. 
  16. ^ Westenhöfer, M. (1942). Der Eigenweg des Menschen. Mannstaedt & Co. 
  17. ^ Scanned image of New Scientist article of 17 March 1960
  18. ^ Sauer, C O. (1960). "Seashore - Primitive home of man?". Proceedings of the American Philosopical Society 106 (1): 41–47. 
  19. ^ Morris, Desmond (1967). The Naked Ape. McGraw-Hill. ISBN 0 09 948201 0. 
  20. ^ Morgan, Elaine (1972). The Descent of Woman. Souvenir Press. ISBN 0 285 62700 7. 
  21. ^ Morgan, Elaine (1990). The Scars of Evolution. Souvenir Press. ISBN 0-285-62996-4. 
  22. ^ Morgan, Elaine (1994). The Descent of the child. Souvenir Press. ISBN 0-285-63377-5. 
  23. ^ Morgan, Elaine (1997). The Aquatic Ape Hypothesis. Penguin. 
  24. ^ Morgan, Elaine (2008). The Naked Darwinist. Eildon Press. ISBN 0-9525620-30. 
  25. ^ MacLarnon, A.M.; Hewitt, G.P. (1999). "The evolution of human speech: The role of enhanced breathing control". American Journal of Physical Anthropology 109 (3): 341–363. doi:10.1002/(SICI)1096-8644(199907)109:3<341::AID-AJPA5>3.3.CO;2-U. 
  26. ^ Lowenstein, J.M.; Zihlman, A.L. (1980). "The Wading Ape-A Watered-Down Version of Human Evolution". Oceans 17: 3–6. 
  27. ^ a b 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. 
  28. ^ Pagel, Mark; Bodmer,Walter (2003). "A naked ape would have fewer parasites". Proceedings of the Royal Society B: Biological Sciences 270 (0, 07 Aug 2003): S117. doi:10.1098/rsbl.2003.0041.. 
  29. ^ Jablonski, N (2006). Skin: a natural history. University of California Press. ISBN 0520242815. 
  30. ^ Carlson BA, Kingston JD (2007). "Docosahexaenoic acid biosynthesis and dietary contingency: Encephalization without aquatic constraint". Am. J. Hum. Biol. 19 (4): 585–588. doi:10.1002/ajhb.20683. PMID 17546613. 
  31. ^ Roede, Machteld (1991). Aquatic Ape: Fact of Fiction: Proceedings from the Valkenburg Conference. Souvenir Press. ISBN 0 285 63033 4. 
  32. ^ Reynolds, Vernon (1991). Cold and Watery? Hot and Dusty? Our Ancestral Environment and Our Ancestors Themselves: an Overview (in Roede et al 1991). Souvenir Press. pp. 340. ISBN 0 285 63033 4. 
  33. ^ Groves, Colin (with David W.Cameron) (2004). Bones, Stones and Molecules. Elsevier Academic Press. pp. 400. ISBN 0 121 56933 0. 

[edit] External links

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