Water monkey theory

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The water monkey theory (also: water theory , water monkey hypothesis ) is a series of partly speculative hypotheses according to which the ancestors of anatomically modern humans ( Homo sapiens ) are said to have undergone a partly aquatic or amphibious phase in the course of the incarnation . This hypothesis could not prevail in specialist circles.

introduction

The proponents of the aquatic monkey theory are of the opinion that early pre-humans stayed for long periods of time and persistently on and in bodies of water and on shore regions . As a result, some special evolutionary adaptations developed to this habitat, which are characteristic of anatomically modern humans. After this “aquatic phase”, the hominini returned to life exclusively on land.

Anatomical and behavioral characteristics that are used to support this theory are in particular:

historical overview

The first water monkey theory: Westenhöfer's Aquatile Hypothesis

Some of the main arguments of the water monkey theory were put forward as early as 1923 by the Berlin pathologist Max Westenhöfer (1871–1957); a summary of his ideas can be read in his book Der Eigenweg des Menschen, published in 1942 . He believed that an aquatic phase had occurred in the course of human tribal history , and demonstrated this with anatomical comparisons. He ruled out a descent or close relationship of humans to great apes and instead saw humans as direct (because they are just as unspecialized and live in damp) descendants of amphibians and salamanders.

Hardy's “Aquatic Ape Theory” and the further development of this theoretical model

Presumably independently of Westenhöfer, the marine biologist Alister Hardy first thought about this concept around 1930. He read a publication describing the peculiarities of the human subcutaneous fat. Unlike most mammals, this is so firmly attached to the skin that it is lifted when the skin is pulled. Hardy, a marine biologist, associated it with the conditions in whales and considered that humans may have had an aquatic phase in their prehistory. Over the years he gathered more evidence, but hesitated to publish it. It was not until March 1960 that Hardy published his thoughts in the article Was man more aquatic in the past in the popular science journal New Scientist . Hardy explicitly referred to his hypotheses in this article as "speculation"; he has not published a book on the subject.

His hypotheses were taken up ten years later by the British journalist Elaine Morgan and further developed in popular science and in connection with feminist views. Morgan published several works on the subject. Other supporters of the Aquatic Ape Theory include the Belgian general practitioner Marc Verhaegen, the Swedish biologist and scuba diver Erika Schagatay, the IT expert Algis Kuliukas, who lives in Australia, and the Swiss sports scientist Renato Bender and the Swiss Doctor Nicole Bender-Oser, who maintain a joint website on the water monkey theory.

In 1987 a symposium on this hypothesis was held in Valkenburg ( Netherlands ), at which supporters and opponents exchanged their views. The second symposium took place in 1999 in Gent (Belgium) under the title "Water and Human Evolution".

Arguments of the proponents of the water monkey theory

In general, all hypotheses to explain the specific characteristics of humans in the course of evolution are subject to one problem: The arguments relate primarily to comparisons with recent anatomical structures and with bone fossils. For most of the characteristics relevant to evolutionary biology, however, it would be necessary to preserve the soft tissue of the fossils in order to provide evidence. In addition, fossils have shown that the waters near hominini sites “were teeming with hungry crocodiles and aggressive hippos . Our small, defenseless ancestors would not have had a chance in a confrontation with such animals. ”It was also not possible to derive verifiable predictions from the water monkey theory that could have contributed to its further underpinning.

Subcutaneous fatty tissue

Humans are the only primate and, in addition to the aquatic whales, seals and manatees, are the only land-living mammals to have a pronounced subcutaneous fatty tissue (layer of fat) that also has a heat-insulating effect . This gave Hardy the first impetus for his hypothesis. Subcutaneous fat insulates the body better in water than wet hair. However, other scientists see this layer of fat - especially in connection with hairlessness and the sweat glands  - as part of a complicated thermoregulatory system. The subcutaneous fatty tissue should therefore be classified as compensation for the inadequate insulation caused by the lack of hair. Another explanation for this phenomenon is that the fat layer serves as a food reserve and in particular covers the increased energy requirements of the brain when there is a lack of food.

The difference in the proportion of adipose tissue in the body tissue of human infants (comparatively high proportion of fat) compared to great ape infants, who are rather thin, is particularly pronounced. According to the aquatic monkey hypothesis, this protected infants from cooling down in the water when they went into the water with their mothers. However, this hypothesis does not explain the rather poor subcutaneous fat tissue of men compared to the sexes. In addition, the average density of the body of human infants is significantly lower than that of other land mammals, so they have more buoyancy. Another explanatory approach sees this feature as an energy reserve for the infant.

The unusual fat distribution in humans compared to other primates is also cited as an argument in favor of staying in the water regularly. While in other primates the fatty tissue is distributed on the body in such a way that the head, neck and abdomen are well insulated and heat is mainly given off via the (hind) legs, in humans the heat exchange is carried out via the face, neck, shoulders and the upper thorax . The lower half of the body, on the other hand, is well insulated by the fatty tissue on the lower abdomen, buttocks and legs. Representatives of water and bank hypotheses of human evolution interpret this fact as an adaptation to regular wading in the water.

There are also differences in the characteristics of the tissue from person to person. The Icelandic fisherman Guðlaugur Friðþórsson survived for about six hours in the 5 degree cold Atlantic, thanks to a seldom thick subcutaneous fat.

Diving reflex

Diving reflex in babies

A key argument for the hypothesis is the presence of a diving reflex in humans: if an infant is immersed in water, it will not swallow water. Infants are able to hold their breath reflexively until they are about ten months old, and they learn to swim quickly; this will u. a. used in baby swimming courses. The diving reflex slows down the heartbeat while diving and ensures that the brain is supplied with more blood .

Against the interpretation of the diving reflex in terms of the aquatic monkey theory, the objection is that such a reflex can be observed in many land-living mammals and that it is therefore probably an original characteristic of mammals, even those to which no "aquatic phase" is ascribed.

Webbed feet

Most people have a flat area of ​​skin, especially between the fingers and sometimes between the toes, which can be interpreted as a rudiment of webbed feet. Chimpanzees and other great apes should not display this trait. In some people there is an almost complete development of such "webbed feet" ( atavism ). Morgan also interprets these skin coverings as "webbed skins" that were acquired during the aquatic phase and may have been partially reduced again. Langdon counters this by saying that these "webbed skins" are fully developed in fetuses of all primates and are reduced before birth. In humans, the reduction of the “webbed feet” is incomplete because humans are intrinsically neoten , which means that typical characteristics of the youthful stages are retained into adulthood. Possibly, however, this is only a consequence of the shortened pregnancy and the associated bringing forward the birth, which allows passage of the birth canal despite the tripling of the later brain volume and the associated increase in head circumference.

The upright walk

The upright gait and the restructuring of the basin are offered as further evidence for the water monkey hypothesis. If apes are forced to go into the water, then they are directed generally go on and on its hind legs. If people have been in and near the water for a long time and have moved swimmingly, then they have to adapt to the water in a streamlined manner. That explains the tilting of the pelvis and the shifting of the legs under the body.

By paleoanthropologists several hypotheses to the emergence of upright walking are discussed in the ancestors of anatomically modern humans that do not require reference to an "aquatic phase" (see main article).

The hairline

Human body hair has a streamlined pattern that corresponds to the direction of the surrounding water when swimming forward. This could have been an intermediate phase of adaptation before the skin was lost. However, this phenomenon can also be explained by rainwater running off faster when walking upright. Perhaps for the same reason, other land-dwelling mammals (such as dogs) have a very similar pattern in their hairline.

Nudity

The sparse hair of humans is also cited as an argument for the water monkey hypothesis. It is pointed out that hairlessness in water offers less flow resistance than fur. In addition, the function of the fur for protection against UV rays in amphibious lifestyle is less important, except on the head. Another thesis points to a selection of "heavily hairy" water monkeys due to the cold problem with wet fur. So it is not so much the efficient swimming adaptation that has taken place, but the general adaptation to shallow water areas.

Several hypotheses about the loss of hair in the ancestors of anatomically modern humans are discussed by paleoanthropologists, who do without reference to an "aquatic phase" (see main article).

Sense of smell

Another argument is the reduced sense of smell in humans. According to Morgan, the sense of smell is stunted because it has little meaning in water. The perception of smells in water is very possible, but only with appropriately adapted olfactory organs, such as with sharks and other fish. However, primates' sense of smell is primarily adapted to the transmission of scents through the air. Morgan concludes that the sense of smell has diminished because it was no longer useful in water. As a counter-argument it is mentioned that the hypothetical aquatic monkey must have lived in the water almost all the time so that a reduction in the sense of smell does not represent a selection disadvantage. However, due to the very incomplete adaptation of the aquatic monkey to the water, this is unlikely. Morgan also fails to take into account that all dry-nosed monkeys , a subordinate of the primates that also include humans, have a poorly developed sense of smell, while mammals that are strongly attached to water, such as otters, beavers, water shrews or even seals, have a very good sense of smell.

Nutritional needs

The proponents of the aquatic ape theory also interpret the nutrient needs of humans as an indication of a water-bound way of life. Some nutrients that are important for the development of the brain such as DHA , EPA , iodine and taurine are only available in sufficient quantities in water.

A study published in 2019 found that bonobos in the Congolese Salonga National Park meet their iodine needs by consuming aquatic plants. Some of the aquatic plants examined have iodine levels that are almost as high as in seaweed . Terrestrial plants in the same habitat, on the other hand, did not have a high iodine content. The authors of the study see this as a possible explanation of how people away from the coast could have met their iodine requirements.

The objection is made that the consumption of meat can also provide the nutrients mentioned in sufficient quantities.

Tear fluid and sweat

However, the salinity of human tear fluid is taken as evidence of a marine episode of our ancestors . With an average salinity of 3.5%, this is in the range of sea ​​water . This concentration is typical of marine mammals. Terrestrial mammals, on the other hand, have i. d. As a rule, significantly less salts in their tear fluid (exception: the elephant , for which a descent from marine ancestors is suggested).

As an indication of marine ancestors, the "wasteful" high salt content of human sweat - compared to other mammals - is interpreted. For example, it could have been used to eliminate superfluous salts that were ingested through food.

Parasites

Practically all parasites that are dependent on humans for their life cycle and whose occurrence is bound to water (e.g. Plasmodium vivax , Plasmodium ovale , Plasmodium falciparum , Schistosoma haematobium , Dracunculus medinensis , Brugia timori , Onchocera volvulus , Wuchereria bancrofti ) come from Africa - that is, from that part of the world where hominization began. According to some authors, the most plausible explanation for the inevitable binding of a large number of water-bound parasites to humans is the assumption of a long coevolution, which would presumably presuppose an early, intensive contact with the water.

Fossil finds

As a further indication, reference is made to findings from many early hominid sites, which prove that the remaining bones were embedded in aquatic sediments (rivers, lakes). This applies to

Only one site ( Laetoli ) shows no aquatic sediments, but volcanic tuffs.

Later findings of Australopithecus africanus (2 million years ago), however, are often not in an aquatic context.

When interpreting these findings, however, it must be taken into account that in the sediments of rivers and lakes there is a significantly higher probability of fossilization of organic matter (e.g. bones) than if the bones are on the surface of the earth - especially in the vicinity of water points. stay where they are and be trampled on by herd animals. The discovery of hominid fossils in aquatic deposits is therefore no support for the aquatic monkey theory.

In fossil Neanderthals, auditory canal exostoses have been found with remarkable frequency . Corresponding changes in the auditory canal were found in around half of the fossil Neanderthals. The frequency of this disease, also known as surfer's ear , indicates regular exposure to (cool) water. Further evidence for this theory are finds of tools made from mussels, which could possibly only be collected by diving.

Kuliuka's wading monkey model

A female gorilla crossing a body of water

In his master's thesis in 2001, the London anthropologist Algis Kuliukas examined the aquatic monkey hypothesis against the background of current research results on hominid fossils and behavioral research. He modified and specified the model to a "wading ape model" to explain the two-legged locomotion of humans. At the same time, he tried to cite criteria for verifiability: if the wading monkey model applies, recent great apes would also have to wade when they are encouraged to go into the water. If, on the other hand, they step into the water on four feet, the model would be refuted.

In fact, lowland gorillas living in swampy terrain are known to display two-legged wading when entering the water. It is also known from the literature that this behavior also occurs in orangutans , chimpanzees and bonobos .

Subsequent studies on bonobos in a wildlife park near Brussels showed that these great apes (genetically most closely related to humans) only walked upright to 2 percent on land. Once they were partially in the water, the rate rose to 50 percent. They almost always used their arms to keep their balance. In bonobos that were completely in the water, 92 percent of the observed gait was upright, almost always without arm support.

In order to maintain the correct historical perspective, it is important to recognize that Kuliukas' theses are nothing new in the water monkey discussion. As an example, the following statement is from an article on the evolution of bipedalism of humans to mention that in 1997 the Anthropological Gazette was published:

“The advantages of walking upright can be understood through the versatility of this mode of locomotion in a semi-aquatic way of life. The bipedic of the early hominids cannot be described as an ideal adaptation to an isolated mode of locomotion, because the human biped covers a wide spectrum of locomotor demands such as diving, swimming, wading , climbing trees and rocks and terrestrial locomotion. "

Furthermore, it seems questionable to make the confirmation or refutation of the water theory dependent on a single behavioral characteristic (wading in great apes). The most important aspect of this theory is based on the consideration of various human characteristics, which are interpreted as convergences to the mosaic of characteristics of other living beings. And finally, even before Kuliukas' theses were formulated, it was known that primates (including great apes) often wade in shallow water, so that the order commonly used in science, "make hypotheses - check hypotheses", was not followed here. Kuliukas nevertheless deserves recognition in the water theory debate, among other things for his attempt to provide a unified definition of water theory.

Other "aquatic" primates

In connection with the sometimes vehement controversy over the water monkey hypothesis, the question arises whether the postulated adaptation of human ancestors to water is a unique process in the group of primates.

Indeed, there are at least three examples of an independent secondary transition of monkeys to a semi-amphibious way of life:

  • the proboscis monkey ( Nasalis larvatus ), which lives in the rainforests of the lowlands and the mangrove swamps of Borneo . These animals belong to the so-called slim monkeys and are characterized by good swimming and diving abilities and a large nose. In females this resembles the human nose, in males it is extremely large ( sexual dimorphism ).
  • the crab monkey ( Macaca fascicularis ), which occurs in Southeast Asia from Myanmar to Thailand , Indonesia to the Philippines . Long-tailed macaques belong to the baboon-like family . They live in forests, preferably near water, also on the seashore. These animals swim and dive frequently. Their favorite food is crabs, which they dig up and wash on the beach. You dive with your eyes open. The washing of the food (also fruits are washed) is not considered an inherited, but culturally transmitted behavior.
Japanese macaques in a hot spring
  • the Japanese macaque ( Macaca fuscata ), which also belongs to the baboon-like family. He lives on the Japanese islands and likes to bathe in hot springs, especially in winter. A macaque population on the island of Kōjima has been under scientific observation since 1948. The female Imo from this population, who invented the washing of food in 1953, became particularly well known. This behavior has since established itself through tradition . Later, the behavior of washing food in the sea and adding salt to it also established itself. Since then, marine life has established itself surprisingly quickly in this group of macaques, although Japanese macaques generally avoid the sea. Members of this population since then developed swimming, diving, and the use of seaweed as food. In addition, these monkeys began to use their hands to carry the food and to walk longer distances (up to 30 m) on two legs. In the early 1980s, the Kōjima macaques began eating raw fish.

What all three examples have in common is that although these species are still primarily land dwellers or tree dwellers, they have also at least partially developed the water habitat. Basically, the blueprint of primates is also suitable for developing a secondary aquatic way of life.

The example of the Japanese macaques from Kōjima shows that when discussing models of hominization, not only the classic evolutionary mechanisms ( mutation / selection ) have to be taken into account. Rather, new behaviors can arise in monkeys through discovery, learning and passing on and - regardless of inheritance - be passed on over generations ( memes ). Such new behaviors can - as the Japanese macaques show - lead to changed living conditions including a change in habitat and a change in the ecological niche and thus have an effect on the evolutionary processes.

This can happen surprisingly quickly, in the case of the Japanese macaques within barely 50 years. External ecological factors (climatic changes, geological changes, etc.) do not necessarily have to have had an impact; rather, new food preferences and behaviors could have emerged, which then changed the way of life and the habitat of human ancestors. This would create different environmental and thus selection conditions, which would now favor the implementation of genetically determined adaptations.

literature

items

  • Renato Bender, Marc Verhaegen, Nicole Oser: The acquisition of a human bipede from the perspective of the Aquatic Ape Theory . In: Anthropologischer Anzeiger. 55 (1), 1997, 1-14, abstract
  • Renato Bender, Nicole Oser: praying mantises, moles and people . Unipress (reports on research and science at the University of Bern, edited by the press office) 95, 1997, pp. 20–26, full text ( Memento from January 28, 2006 in the Internet Archive )
  • Alister Hardy: What more aquatic in the past. In: New Scientist. March 17, 1960, pp. 642–645, full text (PDF)
  • John H. Langdon: Umbrella hypotheses and parsimony in human evolution: a critique of the Aquatic Ape Hypothesis. In: Journal of Human Evolution. Volume 33, No. 4, 1997, pp. 479-494, doi: 10.1006 / jhev.1997.0146

Monographs

  • Renato Bender: The evolutionary basis of human swimming, diving and wading: Convergence research in the terrestrialization hypotheses and in the aquatic ape theory . Diploma thesis at the Institute for Sport and Sport Science, University of Bern, 1999.
  • Nicole Bender-Oser: The Aquatile Hypothesis on the Origin of Man: Max Westenhöfer's Theory and its Significance for Anthropology . Inaugural dissertation to obtain a doctorate in human medicine from the Medical Faculty of the University of Bern, 2004. (a detailed work on the history of the aquatic hypothesis)
  • Carsten Niemitz : The secret of walking upright: our evolution was different . Beck, Munich 2004, ISBN 978-3-406-51606-1 .
  • Elaine Morgan: Children of the Ocean. The human came from the sea (German edition of The Aquatic Ape: A Theory of Human Evolution . Goldmann Verlag, 1989, ISBN 978-3-442-11435-1 )
  • Elaine Morgan: The Myth of the Weak Sex: How Women Became What They Are . Goldmann, Munich 1990, ISBN 3-442-11457-8 .
  • Elaine Morgan: The Aquatic Ape: A Theory of Human Evolution.
  • Elaine Morgan: The Scars of Evolution: What Our Bodies Tell us about Human Evolution.
  • Elaine Morgan: The Aquatic Ape Hypothesis: The Most Credible Theory of Human Evolution.
  • Max Westenhöfer: Man's own path: presented on the basis of comparative morphological studies of species formation and human development . Mannststaedt, Berlin 1942

Web links

Individual evidence

  1. ^ A b John H. Langdon: Umbrella hypotheses and parsimony in human evolution: a critique of the Aquatic Ape Hypothesis. In: Journal of Human Evolution. Volume 33, No. 4, 1997, pp. 479-494, doi: 10.1006 / jhev.1997.0146
  2. ↑ Stephen Ornes: Whatever Happened To ... the Aquatic Ape Hypothesis? discovermagazine.com of September 5, 2007. Here, too, it says: "the aquatic ape hypothesis never got much support from the scientific community."
  3. ↑ HM Dunsworth: Human Origins 101 . Greenwood Press, Westport 2007, Science 101 Series, ISBN 978-0-313-33673-7 , p. 121 .
  4. ↑ Bender-Oser, 2004, p. 129
  5. ^ Alister Hardy: What one more aquatic in the past. In: New Scientist. March 17, 1960, pp. 642–645, full text (PDF) ( Memento from October 19, 2016 in the Internet Archive )
  6. ^ William F. Williams (Ed.): Encyclopedia of Pseudoscience. Taylor & Francis, Hoboken 2013, ISBN 978-1-135-95522-9 , pp. 169 f.
  7. ↑ Marc Verhaegen and the water monkey theory
  8. ↑ Erika Schagatay, Publications
  9. ↑ Algis Kuliukas: Curriculum Vitae 2014.
  10. ↑ aquatic-hypothesis.com
  11. ↑ Nina Jablonski : Why the Aquatic Ape Theory Doesn 'Hold Water. In: Scientific American. Special issue: The Story of Us. Fall 2016, p. 55
  12. ^ Carsten Niemitz: The evolution of the upright posture and gait — a review and a new synthesis . In: Natural Sciences . tape 97 , no. 3 , March 1, 2010, ISSN  1432-1904 , p. 241–263 , doi : 10.1007 / s00114-009-0637-3 , PMID 20127307 , PMC 2819487 (free full text).
  13. ↑ Alva Gehrmann: Natural phenomenon: The secret of the seal man . In: FAZ.NET . ISSN  0174-4909 ( Online [accessed April 28, 2020]).
  14. ↑ Desmond Morris: The Man We Live With. Chapter: "Behavior in the water"
  15. ^ P. Waugh: WAT. University of Oxford
  16. ^ Diet of Homo ancestors. Retrieved April 28, 2020 .
  17. ↑ Bonobos are specifically looking for plants with a high iodine content - Wissenschaft aktuell. Retrieved April 28, 2020 .
  18. ↑ Gottfried Hohmann, Sylvia Ortmann, Thomas Remer, Barbara Fruth: Fishing for iodine: what aquatic foraging by bonobos tells us about human evolution . In: BMC Zoology . tape 4 , no. 1 , July 2, 2019, ISSN  2056-3132 , p. 5 , doi : 10.1186 / s40850-019-0043-z .
  19. ↑ H. & J. Aspöck Walochnik: The parasites of man from the perspective of co-evolution . S. 222-223 ( online [PDF]).
  20. ↑ Erik Trinkaus, Mathilde Samsel, Sébastien Villotte: External auditory exostoses among western Eurasian late Middle and Late Pleistocene humans . In: PLOS ONE . tape 14 , no. 8 , August 14, 2019, ISSN  1932-6203 , p. e0220464 , doi : 10.1371 / journal.pone.0220464 , PMID 31412053 , PMC 6693685 (free full text).
  21. ↑ Paola Villa, Sylvain Soriano, Luca Pollarolo, Carlo Smriglio, Mario Gaeta: Neandertals on the beach: Use of marine resources at Grotta dei Moscerini (Latium, Italy) . In: PLOS ONE . tape 15 , no. 1 , January 15, 2020, ISSN  1932-6203 , p. e0226690 , doi : 10.1371 / journal.pone.0226690 , PMID 31940356 , PMC 6961883 (free full text).
  22. ↑ Bender, Verhaegen, Oser, 1997, p. 1. Also: Bender, 1999, p. 140ff.
  23. ↑ Bibliography on this in Bender, 1999, p. 109ff.
  24. ↑ Proboscis Monkey (Nasalis larvatus).
  25. ↑ Macaca fascicularis - long-tailed macaque.