Aquatic ape hypothesis
Encyclopedia
The aquatic ape hypothesis (AAH) is an alternative explanation of some characteristics of human evolution
which hypothesizes that the common ancestors
of modern humans spent a period of time adapting to life in a partially aquatic environment
. The hypothesis is based on differences between humans and other great apes, and apparent similarities between humans and some aquatic mammals. First proposed in 1942 and expanded in 1960, its greatest proponent has been the writer Elaine Morgan
, who has spent more than forty years discussing the AAH.
While it is uncontroversial that both H. neanderthalensis
and early H. sapiens were better suited to aquatic environments than other great apes, and there have been conjectures suggesting protohumans underwent some adaptations due to interaction with water, the sort of radical specialization posited by the AAH has not been accepted within the scientific community as a valid explanation for human divergence from related primates. It has been criticized for possessing a variety of theoretical problems, for lacking evidentiary support, and for there being alternative explanations for many of the observations suggested to support the hypothesis. Morgan has also suggested that her status as an academic outsider has hindered acceptance of the hypothesis.
in proximity to water with the statement "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."
In 1930 marine biologist Alister Hardy
hypothesized that humans may have had ancestors more aquatic than previously imagined. Because it was outside his field and he was aware of the controversy it would cause, Hardy delayed reporting his hypothesis. 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, not expecting any attention, but it was reported in a national newspaper. This generated immediate controversy in the field of paleoanthropology
. Consequently Hardy published the hypothesis in an article in New Scientist
on 17 March 1960. He defined his idea:
The idea received some interest after the article was published, but was generally ignored by the scientific community
thereafter. In 1967, the hypothesis was briefly mentioned in The Naked Ape
, a book by Desmond Morris
in which can be found the first use of the term "aquatic ape". Writer Elaine Morgan
read about the idea in Morris' book and was struck by its potential explanatory power, becoming its main promoter and publishing six books over the next 40 years. The context of initial presentations of the idea (a popular work and a political text) prevented the AAH from garnering serious interest or an exploration of its scientific merit.
Despite maintaining some popular and scientific interest over several decades, the aquatic ape hypothesis has not been accepted by a large majority of researchers within the field of paleoanthropology
. A small but active number of promoters working outside of mainstream paleoanthropology, non-anthropologists and the occasional professional still cite and bring attention to the AAH, but it has never been completely discredited to its adherents nor fully explored by researchers.
, brackish
or saline water
s (though there has been disagreement and modification of the theory regarding the salinity of the purported watery environment) and suggests comparisons with other aquatic or semiaquatic species with similar characteristics. Some observations include:
The timelines hypothesized for a period of adjusting to aquatic living vary from the Miocene
about 6 million years ago, to nearly 2 million years ago in the late Pliocene
or early Pleistocene
. It is also theorized that the semi-aquatic phase occurred when protohumans migrated along the southern Asian coastline during a previous ice age when sea level
s were considerably lower; this is also proffered as a reason why human fossils are not found in aquatic habitats, as those regions were inundated when the polar ice caps melted.
to support its claims. It is also described as lacking parsimony, despite purporting to be a simple theory uniting many of the unique anatomical features of humans.
Though describing the hypothesis as plausible, Henry Gee
went on to criticize it for being untestable, as most of the evolutionary adaptations described by Morgan would not have fossilized. Gee also stated that, while purely aquatic mammals such as whales show strong skeletal evidence of adaptation to water, humans and human fossils lack such adaptations; that there are many hypothetical and equally plausible scenarios explaining the unique characteristics of human adaptation without involving an aquatic phase of evolution; and that proponents are basing arguments about past adaptations on present physiology, when humans are not significantly aquatic. There is ultimately only circumstantial evidence
to suggest, and no solid evidence to support the AAH. ScienceBlogs
author Greg Laden has described the AAH as a "human evolution theory of everything
" that attempts to explain all anatomical and physiological features of humans and is correct in some areas only by chance. Laden also states that the AAH was proposed when knowledge of human evolutionary history was unclear, while more recent research has found that many human traits have emerged at different times over millions of years, rather than simultaneously due to a single evolutionary pressure.
. However, this idea has been called a caricature of the actual environments in which protohumans are thought to have evolved, and presents a false dichotomy
, as more recent theories propose a tree or forest-based habitat providing the driving forces for adaptation, and a straw man
of the actual theories and arguments used in the study of paleoanthropology. The belief that wading into shallow water would help proto-humans avoid dry-land predation discounts the risks presented by aquatic animals such as crocodile
s and hippopotamus
es that present a current risk to Africans living near bodies of water, and that protohumans lacked the fangs, claws or size to defend themselves from these threats.
The susceptibility of humans to waterborne parasites
have been suggested as evidence against the AAH, though the presence of certain parasites that appear to co-exist with humans has also been presented as evidence for the AAH.
Generally the evidence provided for the AAH is equally well accounted for by land-based adaptations without needing to posit an aquatic phase of human development. In addition, the AAH is contradictory in several places; the AAH theorizes humans developed some unique skin features due to adaptation to water, but other features emerged after leaving the habitat, and the specialization that is hypothesized for an aquatic life are uneven, with humans lacking many truly specialized features of aquatic species (such as head shape, repositioned nostrils and streamlining of the body). Parallels made by proponents of the AAH between humans and the proboscis monkey
, which shows mainly behavioral adaptations to a water-based habitat, contradicts any claims of anatomical evidence for the hypothesis. Many species of modern primates demonstrate some sort of aquatic behaviors (such as swimming, wading or diving) and use of aquatic environments (for thermoregulation
, display behavior, range, diet and predation) but many do not display the traits posited by AAH, suggesting the traits listed above facilitate aquatic behavior rather than evolving as a result of it.
and has been met with significant skepticism. The AAH is thought by some anthropologists to be accepted readily by popular audiences, students and non-specialist scholars because of its simplicity. In 1987 a symposium was held in Valkenburg
, the Netherlands, titled "Aquatic Ape: Fact or fiction?", which published its proceedings in 1991. The chief editor summarized the results of the symposium as failing to support the idea that human ancestors were aquatic, but there is also some evidence that they may have swum and fed in inland lakes and rivers, with the result that modern humans can enjoy brief periods of time spent in the water. The results of the conference were reported in the anthropological press as having rejected the hypothesis. A review of Morgan's book The Scars of Evolution stated that it did not address the central questions of anthropology – how the human and chimpanzee
gene lines diverged – which was why it was ignored by the scholarly community. The review also stated that Morgan ignored the fossil record and skirted the absence of evidence that australopithecine
underwent any adaptations to water, making the hypothesis impossible to validate from fossils.
Morgan has claimed the AAH was rejected for a variety of reasons unrelated to its explanatory power: old academics were protecting their careers, sexism on the part of male researchers, and her status as a non-academic intruding on academic debates. Despite modifications to the hypothesis and occasional forays into scientific conferences, the AAH has neither been accepted as a mainstream theory nor managed to venture a genuine challenge to orthodox theories of human evolution. However, anthropologist Colin Groves
has stated that Morgan's theories are sophisticated enough that they should be taken seriously as a possible explanation for bipedalism.
Morgan's critics have claimed that the appeal of AAH can be explained in several ways:
Human evolution
Human evolution refers to the evolutionary history of the genus Homo, including the emergence of Homo sapiens as a distinct species and as a unique category of hominids and mammals...
which hypothesizes that the common ancestors
Common descent
In evolutionary biology, a group of organisms share common descent if they have a common ancestor. There is strong quantitative support for the theory that all living organisms on Earth are descended from a common ancestor....
of modern humans spent a period of time adapting to life in a partially aquatic environment
Aquatic adaptation
Several animal groups have undergone aquatic adaptation, going from being purely terrestrial animals to living at least part of the time in water. The adaptations in early speciation tend to develop as the animal ventures into water in order to find available food. As successive generations spend...
. The hypothesis is based on differences between humans and other great apes, and apparent similarities between humans and some aquatic mammals. First proposed in 1942 and expanded in 1960, its greatest proponent has been the writer Elaine Morgan
Elaine Morgan (writer)
Elaine Morgan OBE is a Welsh writer for television and also the author of several books on evolutionary anthropology, especially the aquatic ape hypothesis: The Descent of Woman, The Aquatic Ape, The Scars of Evolution, The Descent of the Child, The Aquatic Ape Hypothesis, and The Naked Darwinist...
, who has spent more than forty years discussing the AAH.
While it is uncontroversial that both H. neanderthalensis
Neanderthal
The Neanderthal is an extinct member of the Homo genus known from Pleistocene specimens found in Europe and parts of western and central Asia...
and early H. sapiens were better suited to aquatic environments than other great apes, and there have been conjectures suggesting protohumans underwent some adaptations due to interaction with water, the sort of radical specialization posited by the AAH has not been accepted within the scientific community as a valid explanation for human divergence from related primates. It has been criticized for possessing a variety of theoretical problems, for lacking evidentiary support, and for there being alternative explanations for many of the observations suggested to support the hypothesis. Morgan has also suggested that her status as an academic outsider has hindered acceptance of the hypothesis.
History
In a 1942 book, the German pathologist Max Westenhöfer published the idea of humans evolvingEvolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
in proximity to water with the statement "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."
In 1930 marine biologist Alister Hardy
Alister Hardy
Sir Alister Clavering Hardy, FRS was an English marine biologist, expert on zooplankton and marine ecosystems...
hypothesized that humans may have had ancestors more aquatic than previously imagined. Because it was outside his field and he was aware of the controversy it would cause, Hardy delayed reporting his hypothesis. 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, not expecting any attention, but it was reported in a national newspaper. This generated immediate controversy in the field of paleoanthropology
Paleoanthropology
Paleoanthropology, which combines the disciplines of paleontology and physical anthropology, is the study of ancient humans as found in fossil hominid evidence such as petrifacted bones and footprints.-19th century:...
. Consequently Hardy published the hypothesis in an article in New Scientist
New Scientist
New Scientist is a weekly non-peer-reviewed English-language international science magazine, which since 1996 has also run a website, covering recent developments in science and technology for a general audience. Founded in 1956, it is published by Reed Business Information Ltd, a subsidiary of...
on 17 March 1960. He 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.
The idea received some interest after the article was published, but was generally ignored by the scientific community
Scientific community
The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...
thereafter. In 1967, the hypothesis was briefly mentioned in The Naked Ape
The Naked Ape
The Naked Ape: A Zoologist's Study of the Human Animal is a 1967 book by zoologist and anthropologist Desmond Morris which looks at humans as a species and compares them to other animals...
, a book by Desmond Morris
Desmond Morris
Desmond John Morris, born 24 January 1928 in Purton, north Wiltshire, is a British zoologist and ethologist, as well as a popular anthropologist. He is also known as a painter, television presenter and popular author.-Life:...
in which can be found the first use of the term "aquatic ape". Writer Elaine Morgan
Elaine Morgan (writer)
Elaine Morgan OBE is a Welsh writer for television and also the author of several books on evolutionary anthropology, especially the aquatic ape hypothesis: The Descent of Woman, The Aquatic Ape, The Scars of Evolution, The Descent of the Child, The Aquatic Ape Hypothesis, and The Naked Darwinist...
read about the idea in Morris' book and was struck by its potential explanatory power, becoming its main promoter and publishing six books over the next 40 years. The context of initial presentations of the idea (a popular work and a political text) prevented the AAH from garnering serious interest or an exploration of its scientific merit.
Despite maintaining some popular and scientific interest over several decades, the aquatic ape hypothesis has not been accepted by a large majority of researchers within the field of paleoanthropology
Paleoanthropology
Paleoanthropology, which combines the disciplines of paleontology and physical anthropology, is the study of ancient humans as found in fossil hominid evidence such as petrifacted bones and footprints.-19th century:...
. A small but active number of promoters working outside of mainstream paleoanthropology, non-anthropologists and the occasional professional still cite and bring attention to the AAH, but it has never been completely discredited to its adherents nor fully explored by researchers.
The hypothesis
The AAH suggests that many of the features that distinguish humans from their nearest evolutionary relatives can be explained through a period of aquatic adaptation in which protohumans spent time wading, swimming and feeding on the shores of freshFresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...
, brackish
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...
or saline water
Saline water
Saline water is a general term for water that contains a significant concentration of dissolved salts . The concentration is usually expressed in parts per million of salt....
s (though there has been disagreement and modification of the theory regarding the salinity of the purported watery environment) and suggests comparisons with other aquatic or semiaquatic species with similar characteristics. Some observations include:
- Bipedalism out of water causes considerable problems for the back, knees and organs, while water would support the joints and torso and permit breathing
- Humans are relatively hairless compared to great apes, similar to the hairlessness of land-dwelling rhinocerosRhinocerosRhinoceros , also known as rhino, is a group of five extant species of odd-toed ungulates in the family Rhinocerotidae. Two of these species are native to Africa and three to southern Asia....
and elephantElephantElephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
, which both have aquatic ancestors; what body hair humans do have also follows water flow-lines - Increased subcutaneous fat for insulation, especially in human infants
- A descended larynx
- A hooded noseHuman noseThe visible part of the human nose is the protruding part of the face that bears the nostrils. The shape of the nose is determined by the ethmoid bone and the nasal septum, which consists mostly of cartilage and which separates the nostrils...
, muscular nostril aperture control and the philtrumPhiltrumThe philtrum , is a medial cleft common to many mammals, extending from the nose to the upper lip, and, together with a glandular rhinarium and slit-like nostrils, is believed to constitute the primitive condition for mammals in general...
preventing water from entering the nostrils - Extensive coverage of the skin by sebaceous glandSebaceous glandThe sebaceous glands are microscopic glands in the skin that secrete an oily/waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals...
s - The requirement of the human brain for certain nutrients, including iodineIodineIodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
and some essential fatty acidEssential fatty acidEssential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them...
s which are most easily found and absorbed in seafood - Voluntary breath control which allows diving and swimming, and a more streamlined shape compared to other apes
- The mammalian diving reflexMammalian diving reflexThe mammalian diving reflex is a reflex in mammals which optimizes respiration to allow staying underwater for extended periods of time. It is exhibited strongly in aquatic mammals , but exists in a weaker version in other mammals, including humans. Diving birds, such as penguins, have a similar...
, which occurs when the head is immersed in cold water - Vestigial webbing between the fingers
- The waxy coatingVernix caseosaVernix caseosa, also known as vernix, is the waxy or cheese-like white substance found coating the skin of newborn human babies.-Composition:...
found on newborns - Certain morphological adaptations within the kidneyKidneyThe kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
The timelines hypothesized for a period of adjusting to aquatic living vary from the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
about 6 million years ago, to nearly 2 million years ago in the late Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
or early Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
. It is also theorized that the semi-aquatic phase occurred when protohumans migrated along the southern Asian coastline during a previous ice age when sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
s were considerably lower; this is also proffered as a reason why human fossils are not found in aquatic habitats, as those regions were inundated when the polar ice caps melted.
Criticisms
Several theoretical problems have been found with the AAH, and some claims made by the AAH have been challenged as having explanations aside from a period of aquatic adaptation. Review of the individual claims used as evidence for the AAH generally does not support the hypothesis overall, and most of these traits have an explanation within conventional theories of human evolution. Other authors have suggested that wading and other interactions with watery environments may have provided a less extreme but still present role in human evolution.Theoretical considerations
The AAH has been criticized for containing multiple inconsistencies and lacking evidence from the fossil recordFossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
to support its claims. It is also described as lacking parsimony, despite purporting to be a simple theory uniting many of the unique anatomical features of humans.
Though describing the hypothesis as plausible, Henry Gee
Henry Gee
Dr Henry Gee is a British paleontologist, and evolutionary biologist. He is a senior editor of Nature, the scientific journal....
went on to criticize it for being untestable, as most of the evolutionary adaptations described by Morgan would not have fossilized. Gee also stated that, while purely aquatic mammals such as whales show strong skeletal evidence of adaptation to water, humans and human fossils lack such adaptations; that there are many hypothetical and equally plausible scenarios explaining the unique characteristics of human adaptation without involving an aquatic phase of evolution; and that proponents are basing arguments about past adaptations on present physiology, when humans are not significantly aquatic. There is ultimately only circumstantial evidence
Circumstantial evidence
Circumstantial evidence is evidence in which an inference is required to connect it to a conclusion of fact, like a fingerprint at the scene of a crime...
to suggest, and no solid evidence to support the AAH. ScienceBlogs
ScienceBlogs
ScienceBlogs is an invitation-only blog network and virtual community. It was created by Seed Media Group in 2006 to enhance the public understanding of science. , ScienceBlogs hosted 75 blogs dedicated to various fields of research. Each blog has its own theme, specialty, and author and is not...
author Greg Laden has described the AAH as a "human evolution theory of everything
Theory of everything
A theory of everything is a putative theory of theoretical physics that fully explains and links together all known physical phenomena, and predicts the outcome of any experiment that could be carried out in principle....
" that attempts to explain all anatomical and physiological features of humans and is correct in some areas only by chance. Laden also states that the AAH was proposed when knowledge of human evolutionary history was unclear, while more recent research has found that many human traits have emerged at different times over millions of years, rather than simultaneously due to a single evolutionary pressure.
Habitat
Morgan presented the AAH as an alternative to the "savanna model", which uses very vague descriptive statements portraying protohumans as moving out from forested environments and into a hot dry savannaSavanna
A savanna, or savannah, is a grassland ecosystem characterized by the trees being sufficiently small or widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of C4 grasses.Some...
. However, this idea has been called a caricature of the actual environments in which protohumans are thought to have evolved, and presents a false dichotomy
False dilemma
A false dilemma is a type of logical fallacy that involves a situation in which only two alternatives are considered, when in fact there are additional options...
, as more recent theories propose a tree or forest-based habitat providing the driving forces for adaptation, and a straw man
Straw man
A straw man is a component of an argument and is an informal fallacy based on misrepresentation of an opponent's position, twisting his words or by means of [false] assumptions...
of the actual theories and arguments used in the study of paleoanthropology. The belief that wading into shallow water would help proto-humans avoid dry-land predation discounts the risks presented by aquatic animals such as crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...
s and hippopotamus
Hippopotamus
The hippopotamus , or hippo, from the ancient Greek for "river horse" , is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae After the elephant and rhinoceros, the hippopotamus is the third largest land mammal and the heaviest...
es that present a current risk to Africans living near bodies of water, and that protohumans lacked the fangs, claws or size to defend themselves from these threats.
The susceptibility of humans to waterborne parasites
Waterborne diseases
Waterborne diseases are caused by pathogenic microorganisms which are directly transmitted when contaminated fresh water is consumed. Contaminated fresh water, used in the preparation of food, can be the source of foodborne disease through consumption of the same microorganisms...
have been suggested as evidence against the AAH, though the presence of certain parasites that appear to co-exist with humans has also been presented as evidence for the AAH.
Anatomical and physiological claims
- Hairlessness – Most aquatic mammals that are comparably sized to humans are not hairless, but have dense, insulating fur and swim very well, with fatty layers beneath the skin. Aquatic mammals do not vary greatly in their body hair, while humans do. Hairless skin is also only an advantage for fully aquatic mammals that dive, swim quickly or migrate long distances such as whales and dolphins, and only appears and is an advantage for extremely large aquatic mammals who would overheat with large amounts of body hair, who are fully aquatic and have evolved as an aquatic species for millions of years. The loss of body hair is also explainable through a lower parasite loadParasite loadParasite load is a measure of the number and virulence of the parasites that a host organism harbours. Quantitative parasitology deals with measures to quantify parasite loads in samples of hosts and to make statistical comparisons of parasitism across host samples.In evolutionary biology, parasite...
, and maintenance through sexual selectionSexual selectionSexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...
. Furthermore, while shaving human swimmers to eliminate the little body hair that remains results in a minor decrease in drag, this cannot be extrapolated to a beneficial effect of loss of a full coat of fur, which has been shown to have superior drag reduction ability. While relative hairlessness and hair direction is cited as an adaptation to swimming and diving, there is no evidence of similar skeletal or soft tissue adaptations that are expected to accompany such adaptations. - Breath control – The position, evolutionary timing of changes, and size of the nerve openings in the vertebrae suggest that breath control in humans improved because of the increased complexity and use of speech rather than an aquatic phase of evolution. In addition, breath control is thought to be preceded by bipedalism, which frees the muscles around the upper torso from locomotion and allows breathing rates to occur independent of locomotion. Voluntary speech is thought to be a sufficient evolutionary pressure to explain breath control, independent of other explanations. The vocalizations of dolphins and other aquatic species are not thought to be comparable to humans. In addition, certain birds have speech and breath control comparable to humans, without a phase of aquatic adaptation.
- Diet – a broad terrestrial diet would ensure sufficient access to required essential fatty acids without a high consumption of seafood and the "best" fats found in fish are from cold water fish that did not occupy the same coastal environments as humans. In addition, the requirements of these fats are very minimal, with no evidence that extra fats would result in an evolutionary pressure towards a larger brain. Humans without access to shoreline foods also develop normal brains.
- Diving reflex – the mammalian diving reflexMammalian diving reflexThe mammalian diving reflex is a reflex in mammals which optimizes respiration to allow staying underwater for extended periods of time. It is exhibited strongly in aquatic mammals , but exists in a weaker version in other mammals, including humans. Diving birds, such as penguins, have a similar...
is exhibited by terrestrial mammals as well as aquatic ones, and humans have not been compared to other living hominoids; there is not enough information on for this reflex for it to be used to support the AAH. - Body fat – the subcutaneous fat distribution in humans is more similar to a domesticated animal than an aquatic one, and is nearly identical to that of other primates. The subcutaneous fat of aquatic mammals and humans also seems to serve different uses – it forms the streamlined shape of seals, while in humans it is used for sexual selectionSexual selectionSexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...
. In addition, the distribution of fat and blood vessels allows for improved thermoregulationThermoregulationThermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
, as hot blood from the body can bypass the fat to radiate heat through the skin. - Bipedalism – the disadvantages cited for bipedalism within the AAH are often the result of comparing humans to medium, terrestrial quadrupeds, but the evolution of humans from ape ancestors never included a period of quadrupedal locomotion. Instead, human evolution features mainly brachiationBrachiationBrachiation is a form of arboreal locomotion in which primates swing from tree limb to tree limb using only their arms.- Brachiators :...
, suspension and climbing as the primary method of transportation, with a gradual increase in bipedal locomotion over time. In addition, the elongated lower limbs of humans, which is explained as improving swimming speeds, appears only after the evolution of the HomoHomo (genus)Homo is the genus that includes modern humans and species closely related to them. The genus is estimated to be about 2.3 to 2.4 million years old, evolving from australopithecine ancestors with the appearance of Homo habilis....
genus. - Descended larynx – the human larynx is not shaped like the larynxes of aquatic animals; it forms and descends as an infant begins to speak, making it easier to aspirate waterPulmonary aspirationPulmonary aspiration is the entry of material from the oropharynx or gastrointestinal tract into the larynx and lower respiratory tract...
and drown. Additionally, a descended larynx is not unique to aquatic animals, and permanently or temporarily descended larynxes are seen in dogs, pigs, goats, monkeys, big catsPantheraPanthera is a genus of the family Felidae , which contains four well-known living species: the tiger, the lion, the jaguar, and the leopard. The genus comprises about half of the Pantherinae subfamily, the big cats...
, deer, and young chimps. Mainstream anthropology explain the descended larynx as an adaptation to improve vocalizations by increasing the number of pronounceable vowels and improving the ability of humans to control their speech. - Nose shape – the shape of the human nose is extremely variable within the species, and believed to be related to climatic adaptations and the warming and moistening of air before it enters the respiratory tract, not to prevent water entry while swimming. In addition, the muscles surrounding the nose show no evidence of having been previously more developed, but are part of a complex of muscles that are specially developed in humans to show emotion and aid in communication.
- Interdigital webbing – Morgan's claims for syndactylismSyndactylySyndactyly is a condition wherein two or more digits are fused together. It occurs normally in some mammals, such as the siamang and kangaroo, but is an unusual condition in humans.-Classification:...
, the presence of webbing between the fingers, were based on the purported "rareness" of birth defects "adding" features normally thought absent from an evolutionary order. Interdigital webbing is not the "addition" of new tissue, it results from the failure to eliminate skin cells connecting the fingers, a process common to all tetrapods. - Sebaceous gland – many aquatic animals have rudimentary or no sebaceous glands. In humans, sebaceous glands become active during puberty, with men having far more than women, while women have much better scent receptors. This suggests the glands are sexually dimorphic for sexual selection rather than waterproofing. In seals that use sebaceous glands for waterproofing, the glands are active from birth and are secreted by hard, keratinKeratinKeratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
ized skin that is very different from human skin. - Swimming – modern humans are inefficient swimmers, with shapes that are not well suited to rapid travel through water. Swimming is also a learned trait, and though newborns are able to propel themselves inefficiently through water, they are unable to lift their faces to breathe.
Generally the evidence provided for the AAH is equally well accounted for by land-based adaptations without needing to posit an aquatic phase of human development. In addition, the AAH is contradictory in several places; the AAH theorizes humans developed some unique skin features due to adaptation to water, but other features emerged after leaving the habitat, and the specialization that is hypothesized for an aquatic life are uneven, with humans lacking many truly specialized features of aquatic species (such as head shape, repositioned nostrils and streamlining of the body). Parallels made by proponents of the AAH between humans and the proboscis monkey
Proboscis Monkey
The proboscis monkey or long-nosed monkey, known as the bekantan in Malay, is a reddish-brown arboreal Old World monkey that is endemic to the south-east Asian island of Borneo...
, which shows mainly behavioral adaptations to a water-based habitat, contradicts any claims of anatomical evidence for the hypothesis. Many species of modern primates demonstrate some sort of aquatic behaviors (such as swimming, wading or diving) and use of aquatic environments (for thermoregulation
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
, display behavior, range, diet and predation) but many do not display the traits posited by AAH, suggesting the traits listed above facilitate aquatic behavior rather than evolving as a result of it.
Reception
The AAH has received little serious scrutiny from mainstream paleoanthropologistsPaleoanthropology
Paleoanthropology, which combines the disciplines of paleontology and physical anthropology, is the study of ancient humans as found in fossil hominid evidence such as petrifacted bones and footprints.-19th century:...
and has been met with significant skepticism. The AAH is thought by some anthropologists to be accepted readily by popular audiences, students and non-specialist scholars because of its simplicity. In 1987 a symposium was held in Valkenburg
Valkenburg aan de Geul
Valkenburg aan de Geul is a municipality in the southeastern Netherlands.-History:Siege and conquest were characteristic of the history of Valkenburg. Each event is withheld, followed by subsequent restorations. This most definitely holds for the castle perched atop of a hill in the middle of the...
, the Netherlands, titled "Aquatic Ape: Fact or fiction?", which published its proceedings in 1991. The chief editor summarized the results of the symposium as failing to support the idea that human ancestors were aquatic, but there is also some evidence that they may have swum and fed in inland lakes and rivers, with the result that modern humans can enjoy brief periods of time spent in the water. The results of the conference were reported in the anthropological press as having rejected the hypothesis. A review of Morgan's book The Scars of Evolution stated that it did not address the central questions of anthropology – how the human and chimpanzee
Chimpanzee
Chimpanzee, sometimes colloquially chimp, is the common name for the two extant species of ape in the genus Pan. The Congo River forms the boundary between the native habitat of the two species:...
gene lines diverged – which was why it was ignored by the scholarly community. The review also stated that Morgan ignored the fossil record and skirted the absence of evidence that australopithecine
Australopithecine
The term australopithecine refers generally to any species in the related genera Australopithecus or Paranthropus. These species occurred in the Plio-Pleistocene era, and were bipedal and dentally similar to humans, but with a brain size not much larger than modern apes, lacking the...
underwent any adaptations to water, making the hypothesis impossible to validate from fossils.
Morgan has claimed the AAH was rejected for a variety of reasons unrelated to its explanatory power: old academics were protecting their careers, sexism on the part of male researchers, and her status as a non-academic intruding on academic debates. Despite modifications to the hypothesis and occasional forays into scientific conferences, the AAH has neither been accepted as a mainstream theory nor managed to venture a genuine challenge to orthodox theories of human evolution. However, anthropologist Colin Groves
Colin Groves
Colin Peter Groves is Professor of Biological Anthropology at the Australian National University in Canberra, Australia.Born in England on 24 June 1942, Colin Groves completed a Bachelor of Science at University College London in 1963, and a Doctor of Philosophy at the Royal Free Hospital School of...
has stated that Morgan's theories are sophisticated enough that they should be taken seriously as a possible explanation for bipedalism.
Morgan's critics have claimed that the appeal of AAH can be explained in several ways:
- The hypothesis appears to offer absolute answers, while orthodox science is qualified and reserved, a situation which has great appeal to students and the public
- Unusual ideas challenge the authority of science and scientists, which appeals to anti-establishmentAnti-establishmentAn anti-establishment view or belief is one which stands in opposition to the conventional social, political, and economic principles of a society. The term was first used in the modern sense in 1958, by the British magazine New Statesman to refer to its political and social agenda...
sentiments - The AAH as developed by Morgan has a strong feministFeminismFeminism is a collection of movements aimed at defining, establishing, and defending equal political, economic, and social rights and equal opportunities for women. Its concepts overlap with those of women's rights...
component, which particularly appeals to a specific, feminist audience - The AAH can be explained simply and easily, lacking the myriad details and complicated theorizing involved in dealing with primary sources and materials
- The AAH uses negative arguments, pointing to the flaws and gaps in conventional theories; though the criticisms of mainstream science and theories can be legitimate, the flaws in one theory do not automatically prove a proposed alternative is true
- The consensus views of conventional anthropology are complicated, require specialized knowledge and qualified answers, and the investment of considerable time to understand.
See also
- Endurance running hypothesisEndurance running hypothesisThe endurance running hypothesis is the theory that the evolution of certain human characteristics can be explained as adaptations to long-distance running.-Persistence hunting:...
- Steller's sea ape
External links
- Presentation by Elaine Morgan at TEDTED (conference)TED is a global set of conferences owned by the private non-profit Sapling Foundation, formed to disseminate "ideas worth spreading"....
July, 2009; Comment on ScienceBlogsScienceBlogsScienceBlogs is an invitation-only blog network and virtual community. It was created by Seed Media Group in 2006 to enhance the public understanding of science. , ScienceBlogs hosted 75 blogs dedicated to various fields of research. Each blog has its own theme, specialty, and author and is not...
by paleoanthropologist Greg Laden - Scuttling the Aquatic Ape Hypothesis by Brian Switek
- Aquatic ape theory: Sink or Swim? – website critical of the AAH