Aquatic ape hypothesis

From Wikipedia, the free encyclopedia
Jump to: navigation, search

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 the anthropologist John Langdon in 1997 who argued that one hypothesis could not explain so many different phenomena.[1] 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.[2]

The caves at Pinnacle Point in South Africa show the systematic exploitation of marine shellfish by humans 170,000 years ago.

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.[3]

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

History[edit]

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.[4][5] 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."[5]

The idea received some interest after the article was published, notably from the geographer Carl Sauer,[6] 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".[7] 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.[8] In the 1950s, the anthropologist Raymond Dart narrowed the focus exclusively to one activity, hunting,[9] 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"[10] 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.

Reactions[edit]

Popular[edit]

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.[11] 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."[12]

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.[13] 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".[14] 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 anthropologists[edit]

The AAH has received little attention from mainstream paleoanthropologists; it is not accepted as empirically supported by the scholarly community,[15][16][17] and has been met with significant skepticism.[18] Some reviewers seem surprised that Morgan had not published in peer reviewed publications.[19]

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.[20]

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.[1]

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.[21][22] 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.[23]

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."[24]

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".[25]

From biologists and physicians[edit]

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,[26] was followed by papers by Marc Verhaegen, a Belgian doctor, exploring possible links with disease,[27] and one from an ENT specialist in London discussing the exostoses found in the ears of swimmers.[28] 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.[29] "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."[30] 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 available in seawater such as iodine.[31]

Awareness of the possibilities in the medical community led to positive reviews of Scars of Evolution in the British Medical Journal[32] as well as one in Nature.

Evidence for a waterside context[edit]

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.[33] 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[edit]

Despite many theories, the reason for human bipedalism has remained elusive. Most primates naturally walk on two feet when wading in deeper water. The water helps them to keep their balance, and repeated experience would slowly overcome the "bent-knees" handicap. After reviewing 30 different explanations of bipedalism, Niemitz proposed a shore dweller hypothesis of wading, though distancing himself from the AAH.[34][35] 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.[36] 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, has not produced the same effects in other primates, so 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.[37] 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, compatible with significant wading.[38]

Fish consumption and brain size[edit]

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.[39] The reason is that brain development is essentially 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, where brains originally developed, but are lacking in inland areas (particularly DHA).[40] 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.[41][29][42] 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.[43] Dry season access to aquatic resources was also a necessary condition for adaption to savanna habitats.[44]

Stewart[45] argues that Clarias catfishes provided an early source of dry season nutrition in the African rift valley.

What has been lacking has been the paleontological evidence that early humans consumed fish in significant amounts earlier than 40,000 years ago.[46] 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.[45] Also the archaeological record of human fishing and coastal settlement is fundamentally flawed due to postglacial sea level rise.[47] 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;[48] in Europe the date of the first consumption of fish has been increased to 115,000[49] and then 250,000 years ago;[50] and in South Africa a coastal colony of anatomically modern humans was crucially dependent on seafood 160,000 years ago.[51] 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.[52] Microscopic analysis of fish food remains extending back to 2m years from the Olduvai gorge has now shown cut marks indicating butchery.[53][45]

According to the director of the Institute of Brain Chemistry and Human Nutrition at Imperial College, London,[54] "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".[55] 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).[56] 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 to diets.[57][58] "Without the availability of iodized table salt, non-coastal (inland) habitats do not provide foods rich enough to meet human iodine requirements."[59]

Inside of ear, with exostoses protecting the ear drum

Auditory exostosis[edit]

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.[60][61] 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.[62] A book by G. P. Rightmire reported exotoses in the skulls of Homo erectus, including one from the Lake Ndutu in the Olduvia Gorge.[63] 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.[64]

Vernix caseosa[edit]

Newborn baby partly covered with vernix

One of the tests of a scientific theory is that it makes predictions that can be fulfilled. Morgan's Descent of the Child drew attention to 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.[65] 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.[66] 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.[55] The function is to deliver fatty acids to the fetal gut.[67]

The discovery that several aquatic mammals show signs that were thought to be uniquely human supports a waterside hypothesis.[55]

See also[edit]

Notes[edit]

References[edit]

  1. ^ a b Langdon 1997.
  2. ^ Tobias 1998.
  3. ^ Archer & Braun 2013.
  4. ^ Reeve, Eric. Book review: "The Aquatic Ape: Fact or Fiction?" (PDF). Genetical Research (Cambridge University Press), Volume 59 Issue 01 (February 1992): p. 64.
  5. ^ a b Hardy 1960.
  6. ^ Sauer, Carl O. (1960). "Seashore–Primitive home of man?". Proceedings of the American Philosopical Society. 106 (1): 41–7. JSTOR 985209. 
  7. ^ Morris, Desmond (1967). The Naked Ape. McGraw-Hill. p. 29. ISBN 0-09-948201-0. 
  8. ^ Morgan, Lewis H (1877). Ancient Society. New York: Henry Holt & Co. p. 10. Retrieved 29 October 2016. 
  9. ^ Dart, Raymond A. (1953). "The Predatory Transition from Ape to Man". International Anthropological and Linguistic Review. v. 1 (4). Retrieved 29 October 2016. 
  10. ^ Morgan 1972, p. 11.
  11. ^ Morgan 2008, p. 12.
  12. ^ Attenborough, David (2016). "The Waterside Ape". BBC Radio 4. Retrieved 31 October 2016. 
  13. ^ Morgan 2008, p. 15.
  14. ^ Morgan 2008, p. 17.
  15. ^ Dunsworth, H.M. (2007). Human Origins 101. ABC-CLIO. p. 121. ISBN 978-0-313-33673-7. 
  16. ^ McNeill, D (2000). The Face: A Natural History. Back Bay. pp. 36–37. ISBN 0-316-58812-1. 
  17. ^ Trauth, M. H.; Maslin, M. A.; Deino, A. L.; Junginger, A.; Lesoloyia, M.; Odada, E. O.; Olago, D. O.; Olaka, L. A.; Strecker, M. R.; Tiedemann, R. (2010). "Human evolution in a variable environment: The amplifier lakes of Eastern Africa" (pdf). Quaternary Science Reviews. 29 (23–24): 2981–2988. Bibcode:2010QSRv...29.2981T. doi:10.1016/j.quascirev.2010.07.007. 
  18. ^ Graham, J.M.; Scadding, G.K.; Bull, P.D. (2008). Pediatric ENT. Springer. p. 27. ISBN 3-540-69930-9. 
  19. ^ White, E. (2005). "The Peer Review Process: Benefit or Detriment to Quality Scholarly Journal Publication" (PDF). Totem: the University of Western Ontario Journal of Anthropology. 13 (1): 52–60. 
  20. ^ Reynolds, Vernon (1991). Cold and Watery? Hot and Dusty? Our Ancestral Environment and Our Ancestors Themselves: an Overview. p. 340.  in Roede 1991
  21. ^ Tobias, Philip. Foreword: Evolution, Encephalization, Environment. p. viii.  in Cunnane & Stewart 2010, pp. vii-xii
  22. ^ Tobias, Philip V (1998). "Water and Human Evolution". Dispatches Human Evolution. Retrieved 16 January 2017. 
  23. ^ Bender, Renato; Tobias, Phillip V.; Bender, Nicole (2012). "The Savannah Hypotheses: Origin, Reception and Impact on Paleoanthropology". Hist. Phil. Life Sci. 34: 147–184. 
  24. ^ Foley, Robert; Lahr, Marta Mirazón (2014). "The Role of "the Aquatic" in Human Evolution: Constraining the Aquatic Ape Hypothesis". Evolutionary Anthropology. 23: 56–59. 
  25. ^ Gee, Henry (2013). The Accidental Species: Misunderstandings of Human Evolution. U of Chicago Press. p. 115. Retrieved 6 January 2017. 
  26. ^ Cunnane, Stephen. "The Aquatic Ape Theory reconsidered". Medical Hypotheses. 6 (1). Retrieved 16 January 2017. 
  27. ^ Verhaegen, Marc (1987). "The aquatic ape theory and some common diseases". Medical Hypotheses. v 24: 293–9. 
  28. ^ Rhys Evans 1992.
  29. ^ a b Crawford & Marsh 1989.
  30. ^ Crawford & Marsh 1989, p. 162.
  31. ^ Crawford & Marsh 1989, pp. 184-5.
  32. ^ Charlton, Bruce (5 January 1991). "How the apes lost their fur". British Medical Journal. 302: 58. doi:10.1136/bmj.302.6767.58. 
  33. ^ Stringer, Chris (4 May 2000). "Coasting out of Africa". Nature. 405: 24–27. 
  34. ^ Niemitz, Carsten (2010). "The evolution of the upright posture and gait—a review and a new synthesis". Naturwissenschaften. 97: 241–263. doi:10.1007/s00114-009-0637-3. Retrieved 4 February 2017. 
  35. ^ Niemitz C (2002). "A Theory on the Evolution of the Habitual Orthograde Human Bipedalism – The "Amphibische Generalistentheorie"". Anthropologischer Anzeiger. 60: 3–66. 
  36. ^ Kuliukas, A. V. (2011). "A Wading Component in the Origin of Hominin Bipedalism": 36–66. Retrieved 4 February 2017.  in Vaneechoutte, Kuliukas & Verhaegen 2011
  37. ^ Kuliukas, A. V. (2013). "Wading Hypotheses of the Origin of Human Bipedalism". Human Evolution. 28 (3-4): 213–236. 
  38. ^ Kuliukas, Algis (2016). A Wading component in the Origin of Hominid Bipedality? (Ph. D. Thesis ed.). University of Western Australia. 
  39. ^ Cunnane, Stephen C.; Harbige, Laurence S.; Crawford, Michael A. (1993). "The Importance of Energy and Nutrient Supply in Human Brain Evolution". Nutrition and Health. 9: 219–235. 
  40. ^ Stewart, Kathlyn M. (2010). "The Case For Exploitation Of Wetlands Environments And Foods By Pre-Sapiens Hominins.": 137–171.  in Cunnane & Stewart 2010
  41. ^ Broadhurst, C. Leigh; Wang, Yiqun; Crawford, Michael A.; Cunnane, Stephen C.; et al. (2002). "Brain-specific lipids from marine, lacustrine, or terrestrial food resources: potential impact on early African Homo sapiens". Comparative Biochemistry and Physiology Part B. 131: 653–673. 
  42. ^ Cunnane, Stephen C. (2010). "Human Brain Evolution: A Question of solving key nutritional and metabolic constraints on mammalian brain development": 33–64.  in Cunnane & Stewart 2010
  43. ^ Reyes-Centeno, Hugo; Hubbe, Mark; Hanihara, Tsunehiko; Stringer, Chris; Harvati, Katerina (2015). "Testing modern human out-of-Africa dispersal models and implications for modern human origins". Journal of Human Evolution. 87: 95–106. 
  44. ^ Wrangham, Richard; Cheney, Dorothy; Seyfarth, Robert; Sarmiento, Esteban (2009). "Shallow-water habitats as sources of fallback foods for hominins". American Journal of Physical Anthropology. 140 (4): 630–642. doi:10.1002/ajpa.21122. 
  45. ^ a b c Stewart 2010.
  46. ^ Stringer & Andrews 2005.
  47. ^ Erlandson, Jon M. "Food for Thought: the Role of Coastlines and Aquatic Resources in Human Evolution".  in Cunnane & Stewart 2010, pp. 125–136
  48. ^ Corbyn, Zoë (2011). "Archaeologists land world's oldest fish hook". Nature. doi:10.1038/nature.2011.9461. 
  49. ^ Stringer, Chris; Andrews, Peter (2005). The complete world of human evolution. Thames and Hudson. p. 79. 
  50. ^ Hardy, Bruce L. 1*, Marie-Hélène Moncel (2011). "Neanderthal Use of Fish, Mammals, Birds, Starchy Plants and Wood 125-250,000 Years Ago". PLoS ONE. 6 (1). 
  51. ^ Marean, Curtis W. (1 August 2010). "When the Sea Saved Humanity". Scientific American. PMID 20684373. 
  52. ^ Joordens, Josephine C. A.; d’Errico, Francesco; Wesselingh, Frank P.; Munro, Stephen; et al. (12 February 2015). "Homo erectus at Trinil on Java used shells for tool production and engraving". Nature. 518: 228–231. doi:10.1038/nature13962. 
  53. ^ Archer, Will; Braun, David R. (2013). "Investigating the Signature of Aquatic Resource Use within Pleistocene Hominin Dietary Adaptations". PLoS ONE. doi:10.1371/journal.pone.0069899.s001. 
  54. ^ "Michael Crawford". Imperial College. Retrieved Feb 18, 2017. 
  55. ^ a b c Attenborough 2016.
  56. ^ Crawford & Marsh 1989, p. 159.
  57. ^ Broadhurst et al. 2002, pp. 659-660.
  58. ^ Venturi, Sebastiano and Michel E. Bégin (2010). "Thyroid Hormone, Iodine and Human Brain Development": 112.  in Cunnane & Stewart 2010, pp. 105–124
  59. ^ Cunnane 2010, p. 47.
  60. ^ Rhys Evans, Peter H. (1992). "The parasunal sinuses and other enigmas: an aquatic evolutionary theory". Journal of Laryngology and Otology. 106: 214–225. 
  61. ^ Wong, Brian J.; Cervantes, William; Doyle, Karen Jo; et al. (1999). "Prevalence of External Auditory Canal Exostoses in Surfers". 125 (9). Arch Otolaryngol Head Neck Surg.: 969–72. PMID 10488981. 
  62. ^ Rhys-Evans, P. H.; Cameron, M. (2014). "Surfer's Ear (Aural Exostoses) Provides Hard Evidence of Man's Aquatic Past". Human Evolution. 29 (1/3): 75–90. 
  63. ^ Rightmire, G. Philip (1990). The Evolution of Homo Erectus: Comparative Anatomical Studies of An Extinct Human Species. Cambridge University Press. p. 51. ISBN 0521308801. 
  64. ^ Okumura, Maria Mercedes M.; Boyadjian, Célia H.C.; Eggers, Sabine (2007). "Auditory Exostoses as an Aquatic Activity Marker: A Comparison of Coastal and Inland Skeletal Remains From Tropical and Subtropical Regions of Brazil". American Journal of Physical Anthropology. 132: 558–567. 
  65. ^ Morgan 1994, p. 162.
  66. ^ "The Scars of Evolution – transcript". BBC. 2005. Retrieved 13 January 2017. 
  67. ^ Ran-Ressler, Rinat R.; Brenna, J. Thomas; Nilson; St. Leger, Judy; Wang, Donghao (2014). "California Sea Lions Have Vernix that Delivers Branched Chain Fatty Acids to the Fetal Gut". ISSFAL. 

Bibliography[edit]