Allan Krill
Edited 12/09/21

(This seems to be the first scientific publication of AAT, and the first to use the term 'aquatic ape theory'. I'm surprised that it is not better known. Allan)

S.C. Cunnane. 
Clinical Research Institute, 110 Pine Avenue West, Montreal, Canada H2W lR7 

Medical Hypotheses 6, 49-58, 1980


Hardy's Aquatic Ape Theory (AAT) proposes that man progressed phylogenetically to the two-legged hairless creature that he is today via a semi-aquatic diversion which probably began during the Pliocene or perhaps as early as the Miocene era. It revolutionizes the human evolutionary story and in the process, challenges the classical anthropoid theory which has been the dominant theory of evolution since the time of Darwin. Possible reasons for the existance of many of man's previously unexplained characteristics (bipedalism, hairlessness, subcutaneous fat, bradycardia and others) is resolved without the proposal of any new or unreasonable hypotheses. Yet teh AAT has been largely ignored. Morris and Morgan have supported the theory in the face of considerable criticism. This paper is a review of the theory and a collection of some of the opposing views presented by contemporary orthodox evolutionists. 


Hardy's Aquatic Ape Theory (1) attempts to account for the absence of a fossil record between Proconsul and Australopithecus a period during which the world climate changed drastically from the mild Miocene to the hot, dry Pliocene epoch. Ape-like forms present at the time must have been under tremendous evolutionary pressure, so it would have been quite reasonable if the road to survival was temporarily diverted to a sea or shore-based life. Hardy based part of his arguments for man's aquatic past on the fact that as animals slowly terrestrialized, rapid proliferation resulted in many animals being forced to search the shores and shallow waters for food. Inevitably, some of them including modern-day water snakes, crocodiles, turtles, whales, dolphins, porpoises, dugongs, manatees, seals (partially), polar bears, otters, water voles, water shrews, duck-billed platypuses, penguins, and many extinct species, notably the great ichthyosaurs and plesiosaurs, returned to a water environment permanently or semi-permanently. Others, such as the pig, hippopotamus, and elephant have, like man, reterrestrialized but retained a number of the characteristics they developed while living in or near the water.  

Hardy acknowledged that Hominidae (.early man and his ancestors) and Pongidae (anthropoid apes) both had an arboreal ancestor. However, the crucial point which for the most point is entirely overlooked, is that part of this ancestral stock could have been forced "by competition from life in the trees to feed on the seashores to hunt for food: shell fish, sea urchins, etc., in the shallow waters off the coast" (2). He assumed that this would occur as naturally and successfully in early man as it did in the other groups cited. Adaptation to a sea or shore-based life probably started with wading and progressed to swimming and possibly diving for crabs, shellfish and other food sources on the sea bottom. 


The theory clarifies the existance of a number of man's features which are inadequately explained by other modern theories: 

1. Humans have a remarkable ability to swim. Their complete dominance over other terrestrial mammals in learning how to swim on and below the surface and their subtle flexibility in the water are prime examples. 

2. Humans have lost most of their body hair, a loss which is characteristic of aquatic mammals. Fur has been maintained in semi-aquatic mammals (polar bears, seals, beavers) that live in temperate or cold climates for the occasions during which the animal is on land. 

3. The retention of head hair is likely due to its vital function as a protection against the suns rays. Two possible reasons for hair loss in aquatic mammals are: the subsequent reduction of resistance during swimming, and once wet, the loss of its original function of keeping the body warm by acting as a poor heat conductor. 

4. The hair tracts on the human body differ considerably from those on apes. Particularly different are those on the back which in man are all directed towards the midline. This is the same direction as water would pass in going around the body while swimming. Thus, before their complete loss, hair tracts would have become organised into patterns of least resistance to water flow. 

5. The presence of subcutaneous fat notably distinguishs man from the other primates. This was the key characteristic which initiated Hardy's hypothesis. Subcutaneous fat is also found in whales, seals and penguins. It appears to function in replacing the hair lost by the warm-blooded aquatic mammals. Hardy noted that the presence of sweat glands in man (where they are more numerous than in most mammals), would allow him to retain the subcutaneous fat eyen in a tropical environment and permit excessive heat loss when necessary. 

6. Humans have retained primitive unspecialized hands while the modern apes have specialized their hands and feet for swinging and hanging. The chimpanzees have specialized in knucklewalking. The latter two groups have arms longer than legs which is opposite to what is found in humans. An explanation is that man may have left the trees considerably earlier than the chimpanzees, and used his feet for walking and hands for feeding. He probably began toddling in shallow water (as do the Japanese monkeys which are trained to feed in the sea). Once in the water, he would have found that much of the body weight was supported and balance was easier to maintain, Having these advantages, progress to efficient walking on land would have been considerably quickened by having taken the diversion through the water. Three advantages become apparent if man evolved via a sea-based stage: he would have quickly gained his balance for bipedal locomotion, he would have had a good food supply, and he would have had a quick escape route from carnivorous predators. 

7. In close relation to the mastery of efficient bipedalism was the retention of the curiously primitive human hand, especially the fingertips, are extremely sensitive. Human hands, especially the finThis development might be explained by the early use of the hands for groping on the seafloor and distinguishing between rocks and shellfish which were probably the primary source of food. Just as the California sea otter does today, humans probably used pebbles to crack open the shellfish. It would have been very simple to learn to use primitive tools on the seashore where by trial and error, the problem of opening their hardshelled seafood could be approached. The progression from the use of seashore pebbles as tools to the efficient use of flints as weapons would then have been a natural, simple step. At this point, probably with the ability to make and control fire, to reinhabit the land. humans would have been prepared 

8. Hardy's concluding point pertained to the relatively sudden appearance of man's permanent fossil record during the Pleistocene. If he did have an aquatic phase this would satisfactorily account for the absence of fossils prior to this period. 


Morris is the only known zoologist to have seriously considered the merits of the AAT and evaluated them objectively. in the Naked Ape (3) but appeared skeptical. He initially referred to the AAT At that time he remained with the orthodox view of man's evolution. Subsequently, he has reversed his position (4), and suggested that although the evidence is still largely speculative, too many of man's characteristics fit an 'aquatic mold' to all be coincidental. He supported Hardy on all the major points. Referring to the function of the human nose and buttocks as postulated by other authors, he was doubtful of an aquatic origin being necessarily involved. The outstanding points mentioned which add significantly to the AAT are the development in man of complex verbal speech and the presence of the physiological mechanism known as bradycardia. Along with the decline in the sense of smell in man, these characteristics are discussed at greater length elsewhere in this paper. He concluded that it remains up to the palaeontologists to settle the controversy unequivocally but the balance of the accumulated evidence is in favour of an aquatic phase in man's evolution. 


Morgan (5) has added a number of useful points which also strengthen the AAT. Implicit to Morgan's argument is her contention that the climate of the Pliocene was much more arid and devastating than is generally suggested by most authors. The climate was severe enough that on the entire African continent no prehuman Pliocene fossil has ever been found. This contrasts considerably with the mention of savanna, grassland, and forest islands described by classical evolutionists. Morgan's other points include: 

1. Most early tools are generally considered to have been fashioned from pebbles. Because wave and sand action are required to round them, pebbles are rarely formed anywhere but on the seashore. It is very reasonable therefor, that tool-crafting may have begun on the seashore. 

2. A number of diving mammals such as the seal, beaver, coypu, and whale have a physiological mechanism known as bradycardia (the diving reflex) which acts to slow heart rate and reduce oxygen consumption by tissues other than the heart and brain during a dive. This mechanism allows the animal to stay submerged longer than would otherwise be possible. Terrestrial vertebrates with the distinct exception of man do not possess this feature (6). In man, submersion of the face alone, particularly in infants, dramatically e'licits the reduction of heart rate and respiration. 

3. Morgan suggested that the retention of head hair was due to the need of a free-floating baby to hang onto something particularly when it came time to suckle from the breast. The development of thicker hair during pregnancy adds weight to this idea. The sex-linked loss of hair during balding in the male could be attributed to lack of need. 

4. With the proposed aquatic adaptation and resulting loss of fur, there would have been nothing for a baby to grasp onto while suckling. Larger breasts in the female and nipples which were located lower would thus become advantageous in the baby's feeding. This feature would have easily arisen because subcutaneous fat was slowly accumulating in most of the rest of the torso. The fat, which would have increased the size of the breasts had the advantage of protecting the fragile sub-tissue, preventing cooling of the milk, and storing nutrients. The only other non-human female with breasts comparable to the human female's is the aquatic group of sea cows. 

5. The observation by Basler (7) that about 7% of all schoolchildren have webbing between their second and third toes, and in a few between all the toes, is suggestive of a vestigial aquatic function. Besides humans only the elephant amoung land mammals has interphalangeal webbing. It, too, is thought to have had an ancestral aquatic phase evolving parallel to humans. The thumb-forefinger webbing in man presumeably never developed further because it was more valuable for it to remain prehensile. 

6. The shape of the human nose contrasts considerably with that of the Catarrhine monkeys (narrow partition between the nostrils) and the Platyrrhine monkeys (nostrils further apart). The development of the cartilaginous bridge over the nostrils may have helped prevent salt water from entering the nose during swimming and diving. However, as Morris noted (4), the human nose is rather inefficient for this purpose. 

7. Many of the human expressions - anger, yawning, defiance, smiling, grining, trembling and teeth-baring may be correlated with the emotions. This is also true in other primates. However, one expression - frowning, is different and peculiar only to humans. Darwin explained this unique feature as having arisen to protect against the over-engorgement of the eyes with blood during screaming. Alternatively, the significantly increased reflection of the sun off the water as compared to the dim light of the forests, would induce frowning as a reflex, protective measure. 

8. The fact that humans are the only primates capable of producing tears suggests that this physiological adaptation parallels that found in marine birds, crocodiles and sea snakes. Thus, it is quite possible that as in other weeping mammals, birds, and reptiles, man developed this trait as a maritime primate. 

9. Alone amoung the primates, humans appear to have developed extensive verbal communication in favor of the sense of smell. As in the present day aquatic mammals speech appears to have taken over the sense of smell which is the primary sense of communication and perception of the lower mammals, reptiles and amphibians. 

10. Early birds and primates both had the problem of living above the ground where winds would blow scents away before they could be usefully interpreted. Both these groups exchanged their sense of smell for improved vision. As a result only the birds and primates amoung the higher chordates have developed colour vision. 

With reference to these last two points, if orthodox theory was correct, i.e. that early humans decended directly to the plains, their olfactory sense would have logically improved, not become inferior, as it has. The sense of smell is retained in lower primates, only for perception of highly specific details of the environment. In humans even this function of smell has been increasingly rejected for the more accurate and efficient visual and verbal communication. Furthermore, the sense of smell is virtually useless near water which would also help explain the decline of this function. 

It seems likely that during the birth of verbal communication in the primates, the use of vision played a primary role. On land visual and olfactory senses have proven adequate for virtually all communication required by any of the animal groups. However, with the intervention of a dramatic environmental change, verbal communication would have rapidly become an important feature in the behavioral repertoire and as such would have become integrated into the natural selection process. The result was that speech, as the truly diverse means of communication, played a very important role in moulding the most intelligent animal to be. 

With the advent of the Pleistocene age the earth's climate presumeably became more hospitable. It was at this time that humans would have begun moving inland to river and lake side settlements. Use of flintstone instead of the now unavailable pebbles, settlement in areas where there were caves (such as are often found near the seaside) and covering the cave floors with furs and straws would all have been natural steps for man during this transition period. Bones would have again begun appearing in fossils. "And we came back sea-changed and different: upright, bare-skinned, omnivorous, tool-using, in the first stages of recovering from the biological emergency, and in the first stage of true verbal communication" (8). 


Up to this point the arguments advocating the AAT, as described by Hardy, Morris, and Morgan have been presented. What follows is a consideration of the opposing arguments. First of all it should be noted that the literature contains scanty reference to Hardy or the AAT. Virtually none of man's features suggested by Hardy to indicate an aquatic evolutionary history are even mentioned by modern-day evolutionists. The discussion that is found is centered on bipedalism, tool-making ability and the loss of hair. Features such as bradycardia, hair tracts, tear secretion and the lack of Pliocene fossils are not described. With the aquatic theory as a comparison, one realises that generally inadequate explanations for the development of bipedalism and nakedness are given elsewhere. However, since we have become used to the idea that man became a great plains hunter by descent from the trees, most of us find it hard to accept that man might have achieved his uniqueness via another perhaps more modest route, especially the sea. 

Evolutionists have not failed to mention the known facts, i.e. that human ancestors were arboreal, that they are now bipedal and terrestrial, or that there is a large gap in the fossil record, but generally speaking they have failed to suggest explanations for the existance of these phenomena logically. For instance, LeGros Clark, who was aware of the 'Pliocene gap' in fossil evidence mentioned that "Nor have any artificially fabricated implements been convincingly shown to have been of earlier date" (9). Shultz, in Howell's book (lo), noted the major human distinctions as a species: early, rapid acquisition of erect posture, later, gradual increase in cranial capacity and recently increased life expectancy. Leakey (11) mentioned that he did not think that there was a "true anthropoid ape" bridging the gap between the Hominids and Pongids. The vital questions - was there parallel evolution of man and the apes? or, why did man come to the ground in the first place? remain undiscussed. 

Morgan suggested that the Pliocene climate was too arid to maintain an evolving animal group for very long. Early man probably would not have been able to stay on in this extreme climate. In effect, she suggested that the Pliocene might have been a 10 million year period of drought. This opinion is not respected by too many other authors. Rather, descriptions such as deforestation and reduction in rainfall causing new ecological changes (12), and an environment ranging from dry grassland to open, wooded savanna (13) are found. Based on this difference of opinion, discrepancies in explanations have followed. Poirier (13) suggested that desert or semi-arid conditions had set in but he felt that 'forest islands' must have remained. Climatic studies of this time do not support either side in particular but this is obviously an important point. 

The gap in the hominid fossil record is classically explained in a variety of ways. As an example, Delfgaauw (14) referred to Teilhard de Chardin's 'law of the missing peduncles' - that in evolutionary terms, there is always a disappearance of every beginning of a new animal group. When, as a result of a mutation, a new species of creatures appears at first its numbers are very small. The chance of one of them being preserved as a fossil is consequently very remote. Only when the species is numerous and widely distributed is there a possibility of uncovering a fossil speciman. Therefore, according to Delfgaauw, it is for this reason that early fossils of man have never been found. The weakness here is that mans tentative beginning must have taken 10 million years, considerably longer than he has taken to become fully established. 

Direct mention of the AAT by some sources has occurred. Its popularity has varied from bad to worse. Napier introduced some scathing comments with the remark that the AAT was "splendid but somewhat speculative". He went on to describe the theory as the "aquatic origin of man", adding that "Sir Alister, unwittingly , was credited as the founder of a new theory of human evolution". He continued with, "(the theory) would, at the same time, have favored retention of head hair to keep the sun from burning a hole in his head" (15). Napier noted that the AAT would require humans learning to swim, (nowhere mentioned by Hardy), which would not have been difficult judging by the ease with which they do it today. "Neither, of course, does the 'aquatic ape' theory explain the retention of hair in certain parts of the body" (16). Hardy does have a possible explanation for the existance of axillary hair, described in a more recent publication (17). Napier concluded that "no doubt e.. a fishing society could have been an important factor in the life of early man" (18). 

Poirier mentioned that there were a number of theories of human evolution, including Tarsoid, Brachiator, Serological, "and finally, for diversity's sake, the aquatic theory" (19). The other theories receive good discussion, wheras Hardy's name is not even mentioned in association with the aquatic theory. "A final suggestion that we mention is not, at least at this stage, to be taken as a serious possibility. This highly ingenious (and unlikely) theory _.. what is the evidence in support of this theory? None of importance that I know of . . . the aquatic theory is merely an oddity" (20). In a more recent publication, Poirier (21) maintained his earlier view, without revising the wording. "A final suggestion to be mentioned is not, at least at this stage, to be taken as a serious possibility . . . this highly ingenious (and unlikely) idea . . . is merely an oddity (22). 

Straus, in reference to T.H. Huxley described him as the "godfather, if not the father, of the anthropoid theory of man's origin . . . he was a master of English prose, and his statements carried, and in most quarters still carry a tremendous weight . . . his concept . . . remains the orthodox one . . . In fact, in one form or another, this anthropoid ape theory has been so often and so continuously exposited and propagandized that it has become almost a fundemental tenet of biological and particularly, anthropological belief, a sort of canon or article of faith" (23). Such strong opinions, which in this case appear to be based more on the qualities of the man (Huxley) than on his theory, are quite common in the anthropological literature. 

LeGros Clark (24) observed that aquatic vertebrates initially acquired terrestrial locomotory and air breathing mechanisms in order to maintain their aquatic mode of life. He reasoned that during times of drought these mechanisms would assist in escaping overland from dried up water bodies to those which were not so. He saw this as being analagous to the Hominids abandoning arboreal life during a much later period and becoming mobile on the grasslands specifically in order to seek out other habitable forest areas. However, for this to have occurred, he assumed that a very specific type of climate must have existed during the dry Pliocene period. Furthermore, this does not explain why man is not arboreal now. 

In the use of rocks as weapons it has been argued that humans learned to throw them in much the same way as chimpanzees do. This is an example of the facts being misconstrued to fit the theory. What is fact is that caged chimpanzees do learn to throw objects when irritated. What is also fact is that free-ranging chimpanzees do not throw rocks as a means of displaying aggression. Thus it is only while caged that chimpanzees have the artificial opportunity to practice and be rewarded in the development of this highly complicated, unnatural skill. Early humans, whether on the grasslands (where, incidently, one rarely finds rocks) or on the seashore where rocks and pebbles are plentiful, probably would not have had the time to accurately throw a rock at a predator as an instantaneous defensive move. They would have had the time to run into the water where most predators do not go. 

Montagu observed that man frequently gathered fish and tortoises from the water. He noted that "Great quantities of the remains of tortoises, catfish, relatively easy to catch and aquatic birds were found .., indicating that at this stage these early men had not yet progressed to the gathering and killing of the juveniles of larger animals" (25). Alternatively, if living near water, these animals and fish would have been man's natural prey. 

Napier (26), in discussing body hair, stated that pubic, chest and facial hair denoted sexual maturity. Also, differences in the amount present conveyed information about masculinity or femininity. He continued, "The hairlessness of Homo Sapiens was claimed by Charles Darwin to be a cooling device and this still seems to be the most likely explnation" (27). He suggested that the cooling effect of sweating "was the critical factor in the selection of hairlessness in early man-the-hunter" (28). However, the subcutaneous fat man possesses serves exactly the opposite function. Thus, without sweat glands, man might as well have retained his hair. 

Classical evolutionists have often referred to sex-linked characterization. As Napier explained, the localization of hair on the front of the body "is in accord with current views of the significance of the face-to-face copulatory position which appears to biologically ancient in man" (29). This, he felt, was supported by the fact that the sexually-signalling organs; the lips, breasts, genitalia, and many errogenous zones are on the front of the body. Why then was it adaptively significant for man to start copulating face-to-face when all the other mammals have retained the dorso-ventral method throughout their evolution? 

Plibeam (30) recognised that the human female was unique among the primates in her possession of prominant breasts. He suggested that their presence indicated permanent sexual maturity. In addition he maintained that the female reproductive cycle changed from being cyclical to continous as a result of the need to remain continuously receptive to the male in order to strengthen the pair-bond. The development of polyestrousness or continuous fertility is poorly understood at best, so the mention of the pair-bond is really only a blanket. 


Morgan suggested an aquatic phase for some other animals whose evolutionary development has always been one of conjecture, She referred in detail to the elephant and hippopotamus; the former on the basis of its immense size, hairlessness, trunk, intelligence, longevity, tusks, and salty tears, and the latter on the basis of i.ts large size, hairlessness, inadquate legs (for terrestrial locomotion only), subcutaneous fat and snout. 

A couple of other authors have discussed these two animals as well and made some interesting comparisons between them and aquatic mammals. LeBarre (31) mentioned the elephant in connection with the whale, porpoise, and dolphin, noting that they are all bigger than their terrestrial counterparts. He observed that the elepheant was unlike most mammals but similar to man with respect to the long dependency of the young on the parents, and to its longevity. It is significant that he came this far towards mantioning the possibility of a common aquatic phase in the ancestry of elephants and aquatic mammals but did not discuss any of the features which would have more positively suggested this idea. Bouliere (32) noted that the elephant was polyestrous, a condition approaching the continuous receptivity of the human female. He also noted that the longevity of the hippopotamus is surpassed only by that of the elephant and man. 


The similarities between present-day humans and aquatic mammals (bradycardia, subcutaneous fat, hairlessness, interdigital webbing, poor sense of smell, and generally high intelligence) are too close to exclude a more proximal relationship than is presently accepted by current anthropological theory. There is insufficient evidence at this time to call the aquatic theory more than an hypothesis. Its main virtue is that the existance of so many of man's anatomical and physiological features are put into perspective without any contradictory suggestions concerning his phylogeny. It may be difficult, if not impossible to unequivocally establish the theory, but that is not so much the point; if we are interested in learning more about our evolutionary niche the aquatic ape theory is a valuable step towards that goal. 


1. Hardy A. Was Man More Aquatic in the Past? The New Scientist 7: 642, 1960. 
2. Hardy A. p. 642 in Was Man More Aquatic in the Past? The New Scientist 7: 642, 1960. 
3. Morris D. The Naked Ape. Jonathan Cape, London, 1967. 
4. Morris D. Man-Watching. Jonathan Cape, London, 1967. 
5. Morgan E. The Descent of Woman. Bantam, New York, 1973. 
6. Andersen HT. Physiological Adaptations in Diving Vertebrates. Physiological Reviews 46: 212, 1966. 
7. Morgan E. p. 36 in The Descent of Woman. Bantam, New York, 1973. 
8. Morgan E. p. 160 in The Descent of Woman. Bantam, New York, 1973. 
9. LeGros Clark WE. p. 175 in The Fossil Evidence for Human Evolution. University of Chicago Press, Chicago, 1967. 
10. Howells WW. Ideas on Human Evolution. Harvard University Press, Cambridge, 1962. 
11. Leakey LSB. The Progress and Evolution of Man in Africa. Oxford University Press, New York, 1961. 
12. Montagu A. The Human Revolution. Bantam, New York, 1965. 
13. Poirier FE. Fossil Man. An Evolutionary Journey, CV Mosby, St.Louis, 1965. 
14. Delfgaauw B. Evolution. The Theory of Teilhard de Chardin. Harper and Row, New York, 1965. 
15. Napier J. p. 146 in The Roots of Mankind. Smithsonian Institution Press, Washington, 1970. 
16. Napier J. p. 147 in The Roots of Mankind. Smithsonian Institution Press, Washington, 1970. 
17. Hardy A. Was There a Homo Aquaticus? Zenith 15: 4, 1977. 
18. Napier J. p. 147 in The Roots of Mankind. Smithsonian Institution Press, Washington, 1970. 
19. Poirier FE. p. 69 in Fossil Man. An Evolutionary Journey. CV Mosby, St. Louis, 1965. 
20. Poirier FE. p. 80 in Fossil Man. An Evolutionary Journey. CV Mosby, St. Louis, 1965. 
21. Poirier FE. Fossil Evidence. The Human Evolutionary Journey. 2nd ed. CV Mosby, St. Louis, 1977.
22. Poirier FE. p. 310 in Fossil Evidence. The Human Evolutionary Journey. 2nd ed. CV Mosby, St. Louis, 1977. 
23. Howells WW. .p. 73 in Ideas on Human Evolution. Harvard University Press, Cambridge, 1962. 
24. LeGros Clark WE. p. 186 in The Fossil Evidence for Human Evolution. University of Chicago Press, Chicago, 1967. 
25. Montagu A. p. 45 in The Human Revolution. Bantam, New York, 1965. 
26. Napier J. The Roots of Mankind. Smithsonian Institution Press, Washington, 1970. 
27. Napier J. p. 145 in The Roots of Mankind. Smithsonian Institution Press, Washington, 1970. 
28. Napier J. p. 145 in The Roots of Mankind. Smithsonian Institution Press, Washington, 1970. 
29. Napier J. p. 146 in The Roots of Mankind. Smithsonian Institution Press, Washington, 1970. 
30. Pilbeam D. The Ascent of Man. An Introduction to Human Evolution. Mcmillan, New York, 1972. 
31. LeBarre W. The Human Animal. University of Chicago Press, Chicago, 1968. 
32. Bouliere F. The Natural History of Mamals, AA Knopf, New York, 1967. 58

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