Hardy (1960); Morgan (1972, 1981, 1990, 1997)
Classification: Habitat Compulsion
Mnemonic: Wading
Specific Model: Coastal Foraging
Original Proponent(s): Hardy (1960), Morgan (1972, 1981, 1990, 1997)    
Basic Summary: Bipedal wading in coastal shallows led to hominin bipedalism    
Assessment: Popularity: This model was classified under the subcategory, "wading habitat compulsion", and was ranked 7th most popular out of 9 categories  in the texts reviewed here. 14% referred to this idea specifically.
Simple: #6 /42 (72%)
Detailed: #5 / 42 (70%)
Discussion: ‘Was Man More Aquatic in the Past?’ (Hardy 1960)
Perhaps one of the most controversial ideas on bipedal origins was that brought to the debate by Sir Alister Hardy in 1960 and subsequently developed by Elaine Morgan. His idea was that humans had diverged from the great apes mainly through a phase of greater adaptation to moving through water including shallow coastal waters where, it was speculated, bipedalism would have evolved as a behavioural consequence of foraging for food (Hardy 1960.)

Hardy described his foraging scenario this way:
“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 imagine him wading, at first perhaps still crouching almost on all fours groping about in the water, digging for shell fish, but becoming gradually more adept at swimming. Then, in time, I see him becoming more and more of an aquatic animal going farther out from the shore: I see him diving for shell fish, prising out worms, burrowing crabs and bivalves from the sands at the bottom of shallow seas, and breaking open sea-urchins, and then, with increasing skill, capturing fish with his hands”
Hardy (1960:642.)

At the time of publication there were no reported observations of bipedal wading in extant apes and Hardy’s arguments promoting this scenario were purely theoretical and speculative.

Hardy’s argument continued:
“It seems indeed possible that his mastery of the erect posture arose by such toddling but performed in the water, like children at the seaside. Wading about, at first paddling and toddling along the shores in the shallows, hunting for shellfish. Man gradually went farther and farther into deeper water, swimming for a time, but having at intervals to rest - resting with his feet on the bottom and his head out of the surface: in fact, standing erect with the water supporting his weight. He would have to raise his head out of the water to feed: with his hands full of spoil he could do so better standing than floating It seems to me likely that Man learnt to stand erect first in the water and then, as his balance improved, he found he became better equipped for standing up on the shore when he came out, and indeed also for running. He would naturally have to return to the beach to sleep and to get water to drink: actually I imagine him to have spent at least half his time on the land.”
Hardy (1960:644)

Hardy’s contribution to the literature on this subject was relatively small, compared to that of Morgan who, through a series of popular science books, developed and popularised the idea. A summary of her writings on bipedal origins now follows.

Much of her writings take the form of merely criticising the established accounts of bipedal origins. For example Morgan (1972:13) attacks Morris (1967) and Ardrey (1961) for suggesting that bipedalism evolved due to pressure from hunting. In some of her works, however, she gives much more balanced and detailed arguments about how bipedalism is an unusual form of locomotion in mammals, citing a number of disadvantages with it that must have been outweighed for it to have evolved. She wrote a full chapter on the subject in her 1990 book, where she evaluated the wading idea against two others, labelled ‘the savannah theory’ and the ‘neoteny theory’. The former is the ‘traditional’ view that humans evolved due to a change in habitat from woodland to open grassland, the later is a view picked up from Gould (1977) suggesting that many aspects of ape-human divergence may be explained merely by a shift to more infant-like forms in the adult. In the area of bipedalism, Gould noted that all apes are born with a more upright posture and with the foramen magnum anteriorly orientated as in humans. Only in apes, does the foremen magnum gradually migrate dorsally as more quadrupedalism is practiced. Morgan notes that this is an explanation of ‘how’ but not ‘why’ early hominids may have begun to move in more bipedal way (Morgan 1990:64.)

Her 1994 book, ‘Scars of Evolution’, expanded her theorising on bipedalism to two chapters. The first outlines a much fuller list of the costs of human bipedalism, such as problems with all the body’s weight being transferred through the spine, an increased risk of physical damage through tripping up and falling over and a requirement to ‘re-engineer’ the circulation to pump blood to the extremities and then back up to the brain. The second chapter listed explanations for the phenomenon as proposed in the literature. Among the theories of bipedal origins reviewed is one she labels “the water theory”. Using film footage of the proboscis monkey as her primary source of evidence she describes their reasons for adopting bipedalism in stark, simple terms: “Inundation of the habitat is their incentive for bipedalism. For proboscis monkeys crossing a stretch of water a couple of feet deep, walking upright offers only one single advantage, but it an offer they cannot refuse. It enables them to breathe, whereas if they walked on four legs, their heads would be under water.” Morgan (1994:46) The selective advantage of this, she argues, is much more immediate and straightforward than alternative ‘savannah scenarios’ whereas the costs which she described in her previous chapter, would be far fewer. “In the aquatic scenario the position is reversed.” She wrote. “Walking erect in flooded terrain was less an option than a necessity. The behavioural reward - being able to walk and breathe at the same time - was instantly available. And most of the disadvantages of bipedalism were cancelled out. Erect posture imposes no strain on the spine under conditions of head-out immersion in water … In water, walking on two legs incurs no more danger of tripping over and crashing to the ground than walking on four… Water thus seems to be the only element in which bipedalism for the beginner may have been at the same compulsory and relatively free of unwelcome physical consequences” Morgan (1994:47-48.) The rest of the second chapter argues against one of the main criticisms of the idea, namely that primates in general, and apes in particular, are usually averse to moving in water. Her counter-argument, to suggest that “the apes stayed where they were and the sea came in to them” (Morgan 1994:48), was based on geological findings that the Danakil depression became inundated by sea around 4 million years ago and that this could well have isolated, on newly formed islands, groups of early hominids living in high ground forest. She ends by offering the example of Oreopithecus bambolii, an ape some have considered to be a hominid ancestor, as a possible example of convergent evolution. The evidence does indicate that this species was isolated on a Mediterranean island when sea levels rose there, that it has traits indicating a kind of bipedalism and that it inhabited swampy habitats (Azzaroli 1986.)

Morgan published her next book on the 'aquatic ape hypothesis' in 1997 in which no less than four short chapters discuss the problem of bipedal origins.
The first considers possible precursive forms of locomotion in hominid ancestors and in particular the ‘Hylobatian hypothesis’, which suggests that early bipedal hominids were brachiators and so, like many extant brachiators, they would have practiced bipedalism when on the ground. Morgan reports the consensus in the paleoanthropological literature that our ancestors did not evolve from chimp/gorilla-like knuckle-walkers and suggests “they simply climbed down [from the trees] and stood up” (Morgan 1997:42).The next three chapters then attempt to answer the question posed: ‘why?’

In the first, Morgan primarily addresses the ‘Energy efficiency’ model proposed by Rodman & McHenry and concludes that even though humans might well be 45% more efficient at slow walking than chimpanzees this is largely because we are anatomically specialised for bipedalism whereas they are not. As she puts it “the only thing wrong with it is that it has fallen into what Lewin called the ‘teleological trap’” (Morgan 1997:50.)

In the next, Morgan briefly reviews the diversity of views on bipedal origins by summarising six of them. She ends by noting that “it has been argued that with all the wealth of possible explanations to choose from, the last thing we need is yet another hypothesis” Morgan (1997:61), and yet, another hypothesis is exactly what she alludes to in the fourth chapter: ‘The Wading Ape?’ Her first point in the chapter is to remind readers that the paleoenvironment of perhaps the best known early hominid bipeds, at Hadar, was decidedly wet and wooded and clearly prone to flooding.

She wrote
“There must have been times in such areas when Lucy’s ancestors were unwilling to forego the food supplies still visible on the branches of the partly submerged trees. Seeking to exploit them would have placed them in the one situation where an ape, still largely arboreal, would be obligatorily bipedal as soon as it descended to ground level”
(Morgan 1997:63-64.)

Furthermore, in contrast to the energy efficiency model she notes that
“if we postulate that bipedalism arose as a consequence of wading behaviour, we are in no danger of falling into the teological trap. For an anthropoid ape in three feet of water, the motive for walking upright – however clumsily and laboriously – does not lie in some advantage that might accrue to its descendants. It is immediate and individual and, indeed indispensable. The advantage is that it allows the animal to go on breathing, whereas if it walked on four legs its nostrils would be under water”
(Morgan 1997:64.)

The simplicity of this argument ignores the fact that almost all quadrupedal mammals do not attempt to walk quadrupedally with their nostrils under water, but begin to swim. However, in a way, this adds further strength to it: Only apes and other large primates appear to switch from quadrupedal walking to bipedalism before attempting to swim. Morgan finishes her discussion of bipedal origins by giving examples of bipedalism proboscis monkeys (Nasalis larvatus), chimpanzees (Pan troglodytes) and Gorilla, suggesting that it is in the behavioural context of wading where they are most likely to move bipedally.

The main problem with Hardy’s original idea, and Morgan’s early support of it, is the lack of evidence for a coastal phase in early human evolution. In 1960 Hardy could have been forgiven for speculating that such a phase accounted for the, then, perceived ‘gap’ in the fossil record between Proconsul and Australopithecines as coastal sites are notoriously poor at producing fossils. However, since then, increasing evidence has emerged for early bipedal hominids, each one filling in more of the ‘fossil gap’ and each one geographically distant from coastal habitats, thus making Hardy’s coastal foraging idea seem increasingly unlikely. Morgan followed this line in her first books too.

Talking about scenarios as to why apes might have started to move in water in 1990, she suggested that the “sea came in to them” (Morgan 1990:48.) At least this was backed up with some solid geological evidence for inundation in the north east rift valley, very close geographically to the sites most famously associated with Australopithecus afarensis. However, in her last book, Morgan is very clear and persuasive in promoting the inland, wet and wooded paleohabitats of Hadar as equally compelling environments where early hominids could have begun an evolutionary trajectory towards obligate bipedalism. Indeed, it was the overwhelming common sense of her writing in that fourth book that inspired me to return to academia to pursue this line of study.
Strengths: The Hardy/Morgan version of the wading hypothesis has several strengths. It offers a very clear cut selection pressure for bipedalism - keeping the head above the water to allow breathing, it provides a simple explanation for Pan-Homo-Gorilla divergence and it accounts very well for predation. Perhaps most of all, it sets out to explain practically all the physical differences between humans and our great ape cousins.    
Weaknesses: There are also a few weakneses. Most serious, possibly, is the lack of concordance with the fossil record. Positing a coastal phase prior to and around the split between Pan and Homo is not currently well supported. The original paper by Hardy did not offer any examples from extant apes, although Morgan corrected this to a large extent in some of her books by giving examples of bipedal wading in proboscis monkeys. It also lacks explanations for early hominin postcranial anatomical discrepancies.    
1.1 Survival Value 9 (Good) Keeping the head above the water is judged the most clear cut survival value possible. Wading models such as these are the only ones that offer a scnerio that would potentially kill a quadrupedal hominin.    
1.2 Sexual Selection 5 (Fair) This model was judged neutral by this criterion.    
1.3 Not Teleological 7 (Good) Hardy fails to offer strong arguments for his model in this area, other than to suggest that “it seems … likely that Man learnt to stand erect first in the water and then, as his balance improved, he found he became better equipped for standing up on the shore when he came out, and indeed also for running.” Hardy (1960:644) However, Morgan (1990, 1997) makes some excellent arguments against the ‘teological trap’ that many models of bipedalism suffer from. She stresses that bipedal wading, in contrast to the behavioural contexts of most other models, offers a very real and tangible benefit to the ape in no matter what stage of evolution it was on: it helped it keep its head above water.    
2.1 Improved Food Acquisition 8 (Good) Hardy and Morgan make a strong case that the coastal niche would have provided a plentiful supply of food.    
2.2 Accounts for Predation 9 (Good) Coastal niches are comparatively sparsely populated with predators, compared to savannah habitats and so this model was judged 'good' by this criterion.    
2.3 Why Apes are not Bipedal 9 (Good) Hardy’s assumption is that the ancestors of other African great apes did not migrate to coasts. This is one of the clearest cut explanations for the ape-human divergence that has been proposed. Morgan (1997) revises this context somewhat to the wet and wooded habitats of the Afar triangle. However this still provides both a significant geographical barrier for ape/hominid divergence and also a plausible mechanism for the process of hominization to occur in one lineage but not the other.    
2.4 Extant Analogues 7 (Good) Morgan provided good analogues of bipedal wading behaviour in proboscis monkeys.    
2.5 Applies to Both Sexes 9 (Good) This model applies to both sexes.    
3.1 Hominid Anomalies 2 (Poor) Hardy/Morgan did not attempt to use this model to explain the postcranial anatomy of early bipedal hominins such as australopothecines.    
3.2 Fits Paleoecological Record 2 (Poor) When Hardy published his ideas there was a distinct ‘gap’ in the fossil record between putative hominid ancestors Proconsul and Australopithecus. His model may have been plausible in that context but since 1960 a number of fossils have been found which ‘plug the gap’ and which have all made Hardy’s timescale look increasingly implausible. Morgan has not modified her view of the model greatly based on this new fossil evidence. Although Morgan did go some way to updating the location for ape-human divergence, by placing it inland in Hadar, her timescale remains rather ambiguous and somewhat contradictory..    
3.3 Precursor to Strider and knuckle Walker 7 (Good) The model provides a plausible precursor to both modern striding bipedalism and knuckle-walking.    
4.1 Extended Explanatory Power 9 (Good) The so-called 'aquatic ape hypothesis' sets out to explain practically all the physical differences between humans and the other great apes.    
4.2 Complimentary 4 (Fair) This model was judged worse than neutral by this criteria because its timescale made it contradictory to a few other models.    
4.3 Falsifiable or Testable 0 (Poor) Hardy/Morgan made no falsifiable predictions of their idea.    
References Hardy, A. (1960). Was Man More Aquatic in the Past? New Scientist 7:642-645.
Morgan, E. (1972). The Descent of Woman. Souvenir Press (London)
Morgan, E. (1982). The Aquatic Ape. Souvenir Press (London)
Morgan, E. (1990). The Scars of Evolution. Oxford University Press (Oxford)
Morgan, E. (1997). The Aquatic Ape Hypothesis. Souvenir Press (London)