LANGDON’S CRITIQUE OF THE SO-CALLED “AQUATIC APE HYPOTHESIS”:
IT’S FINAL REFUTATION, OR JUST ANOTHER MISUNDERSTANDING?
Algis V. Kuliukas M.Sc.
Anatomy & Human Biology/ Human Movement Sciences,
University of Western Australia,
35 Stirling Highway,
Crawley WA 6009
Australia
AKuliukas@anhb.uwa.edu.au
Abstract
There has still been no challenge to Langdon’s 1997 critique of the Aquatic Ape Hypothesis (AAH) despite its having a number of
weaknesses. Langdon’s summary of “anatomical evidence for the AAH” seems to have been directed against a somewhat exaggerated
interpretation of Alister Hardy’s (1960) hypothesis that humans were merely “more aquatic in the past” as most of the critique was based on
false comparisons with truly aquatic mammals. Even on this basis, eleven out of twenty-six traits were considered to be “possible aquatic
adaptations” or “consistent with the AAH.”
The treatment of these traits seems to have been rather superficial. For example, Langdon all but ignored the one serious scientific
investigation into the plausibility of the AAH in the literature, Roede et al (1991). Like Langdon’s critique, that study also concluded,
marginally, against the AAH, but clearly it did so only because of evaluating an extreme interpretation of the hypothesis (the likelihood of
there being an ‘aquatic ape’) rather than a mild one (if water had merely acted as an agency of selection in our evolution more than in our ape
cousins.)
It is argued that the mild form of the hypothesis has, in fact, not yet been refuted. Instead, what appears to have happenedis that individuals
have been left to interpret certain ambiguities in arguments put forward by proponents of the hypothesis in their own way and then reject, or
accept it on that basis. Seven years on, significant new evidence has emerged and other AAH-based models have been published which
demand that the debate be reopened and that the AAH attract more serious consideration than it has hitherto received.
In an attempt to add clarity, and in response to recent pleas by Philip Tobias (2002) for a greater emphasis upon the role of water to be in
discussions on human evolution, a simple, unambiguous definition of a mild form of the AAH is here proposed.
Introduction
“Overall, it will be clear that I do not think it would be correct to designate our early hominid1 [hominin] ancestors
as ‘aquatic’. But at the same time there does seem to be evidence that not only did they take to the water from time
to time but that the water (and by this I mean inland lakes and rivers) was a habitat that provided enough extra
food to count as an agency for selection.” Vernon Reynolds (in Cold and Watery? Hot and Dusty? Our Ancestral
Environment and Our Ancestors Themselves: An Overview. In Roede et al (1991:340).
That paragraph, taken from the concluding editorial section of the Valkenberg symposium (Roede et al 1991),
which specifically considered the so-called “Aquatic Ape Hypothesis” (AAH), signals a clear message that the
author believed that the hypothesis, although probably wrong in its extreme (and, perhaps, most commonly
interpreted) form, does deserve consideration in some revised, moderate reconstruction.
That moving through water might have acted as an agent of selection in human evolution has, however, remained
more the target of ridicule than research in the field of paleoanthropology. This state of affairs has remained to this
Throughout this paper the terms ‘hominin’ and ‘hominid’ are used specifically as defined by Cameron (2004:5). ‘Hominin’
refers to humans and their unequivocal ancestors. ‘Hominid’ refers to any great ape (chimpanzee, gorilla or orang-utan),
human or their immediate ancestors. If the term ‘hominin’ is used, the reader should infer that this is referring to an ancestor of
Homo sapiens that is not also an ancestor of any extant ape. If the term ‘hominid’ is used, no such distinction is being inferred.
It could be the ancestor of any ape or human. If the terms are used inside citations, they are repeated without alteration, but the
assumed meaning using the above definition is inserted if deemed necessary.
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day, at least in part, because of the critique of the AAH by Langdon (1997) the only paper published in a
paleoanthropological journal that considered, and rejected it.
Langdon (1997:480) justified his critique by arguing that “the aquatic ape hypothesis continues to be encountered
by puzzled students who wonder why mainstream paleoanthropologists overlook it. If only because of this last
audience, it should not be ignored.”
Langdon makes a good point. Students and lay people who hear about the theory for the first time tend to be open
to it. “That makes sense” is a common reaction. Indeed, bearing this in mind, the whisperingly negative reaction to
the AAH from probably the great majority of professional paleoanthropologists is, perhaps, as interesting as the
hypothesis itself. It has been the partial subject of at least two Ph.D. theses to the knowledge of the author (Neilsen
2003, Williams in progress) and warranted Graham Richards to write a whole chapter on the subject entitled “The
Refutation that Never Was: The Reception of the Aquatic Ape Theory, 1972-1987” (Richards 1991) although
Langdon makes no mention of this angle on the subject in his critique. Whatever the reasons for the lack of serious
attention afforded the AAH by paleoanthropologists in the past, be they some kind of “perceived ‘outsidership’ of
Elaine Morgan”, as argued by Richards (1991:124), or simply bad timing, arguing for the importance of water in
1960 when the general thinking of the consensus was more focused on aridity, Langdon was right to address the
issue.
The interest by new students and the interested lay public in the AAH is as real today as it was in 1997. Indeed it
has remained by far the most popular (if also rather controversial) topic of discussion on internet newsgroups (e.g.
see science.anthropology.paleo on http://groups.google.com/groups) about paleoanthropology for years. However,
a student of human evolution familiar with the literature today might be forgiven for concluding that Langdon’s
critique was the last word on the subject, its final refutation, as no reply has been published since. Indeed, this
might also explain why so few (if any) prospective Ph.D. students have chosen AAH-related subject areas in which
to conduct their research and why, in fact, most students have probably been persuaded not to waste their time
looking into it.
It is with that audience in mind that this counter-critique has been written: Weaknesses in Langdon’s paper deserve
to be challenged; Pro-AAH arguments not covered should be heard, and an altered version of the AAH, modified to
reflect Langdon’s and others’ criticisms, should be aired for scientific scrutiny. It also aims to respond to a recent,
plea from Phillip V. Tobias “to re-examine these claims, much as Langdon (1997) has done” (Tobias 2002:16).
Tobias has been a lone voice in the field of paleoanthropology, in the past few years, calling for his peers to
reconsider the role that water has played in human evolution (e.g. Tobias 1998a).
This paper mirrors the structure of Langdon’s original publication. It critiques his arguments, and outlines
additional AAH-related ideas. It ends by suggesting, for the first time, a simple and unambiguous definition of the
hypothesis that can be rigorously tested.
The ‘aquatic ape hypothesis’ (AAH)… Then
Langdon introduced the hypothesis thus: “The AAH in its present form was first articulated by Alister Hardy in
1960 in an issue of New Scientist magazine featuring the relationship of man and the sea, past present and future.”
Although the phrase ‘in its present form’ is probably out of date six years on, it is true that most proponents of
some kind of AAH take Hardy’s (1960) paper as their starting point. It should be noted however, that the AAH, like
any model of human evolution, is under constant revision in response to criticisms and as new evidence emerges.
Therefore its present form today is not the same as the one Langdon dismissed in 1997. Some of those newer forms
will be discussed later. It should also be noted that Hardy’s ideas are not the only (or indeed the first) to be
articulated in the literature. As we shall see later, there are several AAH variants, each one differing in the proposed
timescale, aquatic habitat and human traits suggested as evidence.
One small but important point about Hardy’s original paper, overlooked by Langdon, was its rather modest title:
'Was man more aquatic in the past?' (my emphasis). Here lies a clue to probably the most common
misunderstanding of the hypothesis. On first hearing the term ‘aquatic ape hypothesis’, reviewers could be forgiven
for understanding that this was an hypothesis which actually postulated that humans evolved from a truly aquatic
ape, in the sense that seals are aquatic mammals. A series of publications (Hardy 1960, Sauer 1960, Morgan 1972,
1982, 1990, 1994, 1998, Cunnane 1980, Ellis 1986, 1991, 1993, 1995, Crawford & Marsh 1989, Verhaegen 1990,
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1993, 1994, Knight 1991, Evans 1992, Wescott 1995, Verhaegen et al 2002, 2001, Kuliukas 2002) never made
such an extreme claim.
At most, some of them have argued that that a move into more littoral habitats shaped a distinct phase of human
evolution, in a similar way to that which, it is postulated, must have happened in the very earliest stages of the
evolution of such aquatic mammals as members of Cetacea, Sirenia and Pinnipidae. That argument, based on
comparative biology, notes that almost every mammalian order contains at least one or two genera or species which
appear to have taken advantage of, at some time in their evolution, more aquatic habitats. It further draws upon
comparative anatomy to see where human traits, which seem to be rather unique in the primates, such as nakedness
and increased sub-cutaneous adipocity, have analogues in Mammalia and identifies aquatic mammals as the best
qualifying taxa (See, e.g. Hardy 1960:642; Morgan 1982:25.)
It is possible, and even likely, that some of these arguments have simply been misunderstood to be arguing for
greater levels of aquatic adaptation than was originally suggested. But it must be noted that both Hardy and Morgan
also made statements which should have made it clear that they were not arguing for anything more than, at most, a
semi-aquatic, or littoral, stage in human evolution. Hardy, for example, wrote: “It may be objected that children
have to be taught to swim; but the same is true of young otters, and I should regard them as more aquatic than Man
has been” Hardy (1960:643.) Even Morgan’s much maligned earliest work ‘Descent of Woman’ contains this
graphical depiction of her thinking on early humans: “At the highest point of their period of aquatic adaptation the
ancestral hominids [hominins], though never as fully marine as the dolphins or sirenians, would probably have been
capable of crossing wide stretches of water under their own steam; and without postulating that at such an early
stage of their evolution they became boat builders, it is highly possible that they would have been aware of some of
the uses of a floating log” Morgan (1972:133.) Crossing stretches of water on logs is not the usual image one has in
mind for mermaids.
It would appear that it was exactly how these early ideas were personally interpreted that determined how well they
were received. If one interpreted them as meaning that it was proposed than humans went through some kind of
‘primate seal’ or ‘merman’ phase, it was rejected. If one interpreted them as merely arguing that man went through
a phase where our ancestors did a lot more swimming and diving than he does today (or more than our ape cousins
do), it is difficult to see what the fuss was all about.
It is argued here that although Langdon and most paleoanthropologists in the time since 1960 have taken the former
view, perhaps we should at least consider the later, more modest, interpretation too. Ideally, we should attempt to
arrive at some kind of definition, so that whatever analysis follows is not based upon personal interpretations of
what one thinks the AAH ought to be, but on a simple and unambiguous statement of what it actually is.
So, assuming a more moderate form of the AAH, the key part to understand in Hardy’s title and his thesis must be
the word ‘more’. If so, the meaning of the AAH would then merely be the hypothesis that human evolution
underwent a phase or phases where our ancestors were merely more aquatic than humans are today and also, by
implication, more aquatic than our ape cousins’ ancestors were, and whose extant survivors are today.
Langdon did no justice to the hypothesis by avoiding all of this complexity, ignoring the clear message in the title
of Hardy’s thesis, and merely defining it’s meaning as “having observed a number of anatomical parallels between
distinctively human traits and marine animals, he [Hardy] proposed that the human lineage had been shaped
evolutionarily by a temporary phase of adaptation to a littoral habitat” (Langdon 1997:480).
Although Langdon began his paper by referring to Hardy’s original2 paper, almost all of it subsequently appraises
the work of a single proponent of that theory, Elaine Morgan. Morgan is certainly the most prolific proponent of the
hypothesis but she is not the only one. It should also be noted that Langdon’s critique was written too late to take
into account Morgan’s latest, and arguably best, work, ‘The Aquatic Ape Hypothesis’ (Morgan 1997), which
addressed a number of the weaknesses Langdon referred to.
Although Hardy’s 1960 article in New Scientist is the most widely attributed original AAH source and is certainly the first
reference to it in an English language scientific journal, the first published work which irrefutably makes a claim that human
ancestry was greatly influenced by water was that of Max Westenhöffer (1942) – Der eigenweg des menschen.
2
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Anatomical evidence for the AAH
About half of Langdon’s critique detailed anatomical traits drawn from modern human anatomy which proponents
of some kind of AAH have suggested as evidence of a more aquatic past. Twenty-six such traits were given equal,
and rather short, treatment. This could be perceived as being rather unfair as Morgan wrote six chapters on just
three of them in her latest book Morgan (1997)). He placed the traits into six categories: Primary evidence –
possible aquatic adaptations; Parallelisms inadequately explained by the aquatic hypothesis; Traits consistent with
the AAH; Primitive traits; Hypothetical reconstructions of past events; and Secondary developments. Langdon
(1997:Table 1:488).
It should be noted that even Langdon categorised 4 traits as “possible aquatic adaptations” (voluntary-breath
holding, enlarged pharynx, thermoregulatory strategy and absence of salt hunger) and 7 as “consistent with the
AAH” (bipedalism, speech, protruding nose, paranasal sinuses, long scalp hair, sebaceous gland distribution, and
apocrine gland distribution) (Langdon 1997:488).
However, throughout the table, and the review generally, Langdon repeatedly appears to be critiquing an extreme
interpretation of the hypothesis. His one line rebuttal “not typical of aquatic animals” was used several times, as if
the AAH was arguing that human ancestors had been aquatic.
Bipedalism
In the first paragraph, Langdon chose to pick out but one piece of reasoning in favour of a wading origin for
bipedalism, the one proposed by Morgan (1990:24-35) that common human lower-back problems, increased risk of
herniation and vascular problems such as fainting and varicose veins associated with bipedalism would have been
reduced in water. In the second paragraph this argument was refuted on the grounds that “authors who wish to
recite the many disadvantages of bipedalism commonly do so by comparing humans to medium-sized terrestrial
quadrupedal mammals” (Langdon 1997:481). No such authors were cited but it was implied that this was Morgan’s
reasoning. Morgan, in fact, only compared humans to apes. Even if one assumes that she meant a medium-sized
terrestrial, knuckle-walking ancestor, this is not a remarkable position to hold as many other prominent
paleoanthropologists (e.g. Rodman & McHenry 1980) also advocate such models.
Langdon then went on to suggest that climbing and suspensory specialisation and the resulting increased use of
bipedal posture and gait in hominins is a more likely explanation of bipedal origins. He misrepresents Morgan by
arguing (Langdon 1997:481) that she “wrongly dismisses these specialisations on the grounds that brachiation is
irrelevant”, when actually, she was merely making the point that, in terms of the associated problems with the
lower back, human bipedality was the opposite of brachiation. She wrote “in fact, as far as the spine is concerned,
brachiating is at the opposite end of the spectrum to bipedalism. For the ape, the weight of the body and legs tends
to stretch the spine and minimise pressure on the disks of cartilage between the vertebrae” Morgan (1990:27.)
His concluding comment on this, “the climbing/suspensory complex both removes our ancestry from conventional
terrestrial quadrupedalism and helps to bridge the gap towards human bipedalism” (Langdon 1997:481), merely
backs the brachiationist model of bipedal origins, one of many. As there are more than twelve other such models
(see Rose, 1991, for a review) and very little consensus exists in the field about them, Langdon’s argument hardly
acts as a strong rebuttal to the aquatic argument for bipedal origins.
In 1997 there was very little data in the literature about ape behaviour in water but even from a theoretical point of
view it is difficult to conceive of any naturally occurring environment where an ape would be free to move in any
direction it chose, but be forced to do so bipedally, other than in waist-deep water.
Since Langdon’s paper, several pieces of data have emerged indicating that extant great apes do, indeed, move
bipedally in water (Karlowski 1996, Doran & McNeilage 1998, Tutin et al. 2001, Parnell & Buchanan-Smith 2001,
Kuliukas 2002) as well as a theoretical paper backing a wading model by the German anthropologist Niemitz
(2002). The wading or wading-climbing hypothesis therefore might appear to be more plausible today than it has
ever been and Langdon’s critique of it should not be regarded as having any significant power of rebuttal at all.
Langdon categorised bipedality in his table as ‘Traits consistent with the AAH’ (Langdon 1997:488) but dismissed
it as “not typical of aquatic animals”. This is just one example of several false comparisons he made on the basis of
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an extreme interpretation of the AAH, and ignores the phylogenetic fact that humans evolved from great apes,
which are very typically, and rather uniquely, bipedal in waist deep water.
The matter of bipedal origins is clearly a complex subject and any proposed model would require far more than a
couple of paragraphs to start to discredit it.
It is not the intention here to line up all of the twenty six traits listed by Langdon again for re-evaluation. Suffice it
to suggest that most of them received an even more perfunctory consideration than did the case of bipedalism.
Although Langdon chose to give each of them apparently equal weighting and list them out, almost as if to make
fun of them, a proponent of the AAH would probably have chosen to emphasise two or three which seem to have
most explanatory power. So with that approach in mind, in addition to bipedalism two others will be given specific
attention now.
Reduction of Body Hair
‘Reduction of body hair’ is discussed in three sentences (Langdon 1997:483) by arguing that although it can be
explained similarly in both terrestrial and aquatic mammals, the aquatic model is not strongly favoured over the
terrestrial one. Again, this is hardly an adequate portrayal of one of the most powerful of the AAH arguments, nor
is it any kind of serious rebuttal.
Morris’ (1967) ‘The Naked Ape’ made the point very well, when it began: “There are one hundred and ninety-three
living species of monkeys and apes. One hundred and ninety-two of them are covered with hair. The exception is a
naked ape self-named Homo sapiens” (Morris 1967:5.) This very odd mammalian characteristic deserves a more
thorough analysis than Langdon chose to give it.
Of perhaps eleven separate evolutionary events of the loss of hair in mammals, at least four may be attributable to
aquatic factors: Those in Cetacea, Sirenia, Hippopotimidae and at least one species of Pinnipedia. Two might be
attributed to large body size: In Elephantidae and Rhinocerotidae. Three may be attributed to subterranean
burrowing: The Naked Mole Rat (Heterocephalus glaber) and members of Xenarthra (Armadillos) and Pholidota
(Pangolins). Leaving just two other instances: Some pigs like the babirusa (Suidae) and Homo sapiens. It is likely
that climate is a contributing factor as virtually all terrestrial naked mammals are tropical.
Discounting large size (on the scale of a rhinoceros or above) and a burrowing ancestry as explanations for human
nakedness, and even ignoring any possibility that pig, elephant (although see Gaeth et al. 1999) and rhinoceros
ancestry may have also been more aquatic in the past, this comparative evidence does suggest that some kind of an
aquatic explanation could be the most likely causative factor for nakedness in humans. This view is supported by
further evidence that in competitive swimmers shaving body hair does significantly improve swimming efficiency
and/or speed through drag reduction (Sharp et al 1988, Sharp & Costill 1989) or through undetermined means
(Kruger et al. 2000).
Alternative explanations have been put forward that were not mentioned by Langdon, for example sexual selection
(e.g. Darwin 1879) and parasite reduction (e.g. Pagel & Bodmer 2003). Sexual selection does at least offer a
reasonable case as to why only humans out of all of the primates would have become naked. As Richard Dawkins,
so eloquently puts it: “Sexual selection produces quirky, whimsical evolution that runs away in apparently arbitrary
directions, feeding on itself to produce wild flights of evolutionary fancy.” Dawkins (2004:223). But, as Dawkins
notes himself, sexual selection is also usually associated with increased sexual dimorphism. In some (e.g. IndoEuropean) human groups there is a clear disparity between male and female body hair, but it does not appear to be
a particularly strong universal human characteristic. Most men have little more body hair than most women.
The parasite reduction hypothesis might be a better explanation, in that it covers both males and females, but any
gain in explanatory strength there, is lost in that it fails to adequately explain why only humans out of all the
primates, and indeed almost all mammals, have adopted this strategy.
In that regard, a link to bipedalism has been offered to make the distinction clearer. Wheeler (1984, 1991, 1992)
argued that the origin of bipedalism was linked to the origin of human nakedness as an adaptation to improve
thermoregulation through evaporative sweat cooling. This would also appear logical, except that evidence from the
analysis of genes involved in melanocytes now seem to indicate that nakedness arose relatively recently, perhaps as
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late as 1.2 Ma (Jablonski 2004) and recent fossil findings (Senut et al. 2001) imply that bipedalism may have
evolved as early as 6 mya, long before nakedness.
Nakedness as an aid to sweat cooling could make some sense, although several mammals, e.g. Equidae, are known
to sweat without being naked and others, e.g. Elephantidae, are naked without sweating. But even this, rather
tenuous, association is only plausible in the context of a habitat that is proximal to reliable sources of fresh water.
In this regard, Langdon’s argument (1997:483) that aquatic explanations for nakedness may not be stronger than
terrestrial ones, misses the point. It is at the juncture between land and water where sweat cooling makes most
sense: There is therefore no contradiction with a moderate form of the AAH. Indeed the best possible way of rapid
cooling, as witnessed by Hippopotomidae, is simply to go for a dip. In this sense, ‘dip-sweat’ cooling could be
justifiably claimed, by proponents of the AAH, to be an aquatic adaptation.
As with the case for bipedalism, the complexity of the arguments for and against a human trait being seen as some
kind of aquatic adaptation was given short shrift in Langdon’s critique and therefore it can hardly be taken as any
valid refutation of the argument.
Subcutaneous fat
Similarly, the unusual amount of subcutaneous fat in humans, especially infant humans, the trait Morgan considers
the most powerful piece of evidence in favour of a more aquatic past (personal comment 2000), receives just four
sentences of discussion.
Langdon (1997:483) explains it thus: “The fat-and-sweat strategy of thermoregulation may be adaptive for a
species that is more concerned about shedding internally generated heat. Insulative fat, rather than hair, permits the
bloodstream to bypass it as needed, taking hot blood from the core of the body to the surface to be radiated or lost
through evaporation.”
If this were true one would expect the “fat-and-sweat-strategy” to be found in other tropical terrestrial mammals
concerned with shedding internally generated heat, when it is clearly not. It would seem to be a very energetically
expensive method for any mammal, especially ones living in drier, more open habitats.
As with the argument for hair loss, Langdon’s argument does not contradict the water-side explanation at all and
does not explain why humans should, unusually, have this requirement more than any other primate. Together with
sweat cooling, it is in a water-side habitat where a mammal is likely to gain most from this kind of arrangement.
The extra buoyancy that a healthy layer of subcutaneous fat gives to people only adds further advantage to the
thermoregulatory benefit Langdon describes.
The specific issue of high human infant adipocity, which begins to accumulate in the last trimester of pregnancy
and accelerates in the last few weeks before birth (Bennet & Brown 1999:982), and explanations for it such as
acting as an energy buffer during the critical period of brain growth (see, e.g. Correia et al 2004), were not
mentioned by Langdon, leaving the impression that his rebuttal of this argument too was rather perfunctory and
unsatisfactory.
Both the reduced body hair trait and the subcutaneous fat were categorised as ‘secondary developments’ (Langdon
1997:Table 1:488), ‘secondary to thermoregulatory strategy’. It could be argued that such a ‘fat-and-sweat’
thermoregulatory strategy works best in water-side habitats and that, therefore, this was as much a vote of support
for the mild form of the AAH as it was a counter-argument against the extreme version.
Other Traits
There were twenty-three other human traits listed in the critique.
Some, such as ‘Breath-holding and speech’, ‘Enlarged pharynx’, ‘Nose’, ‘Respiratory valves’ and ‘Paranasal
sinuses’ could all be grouped under ‘respiratory modifications’ and the AAH argument for all of them could be
summed up as ‘adaptations for swimming and diving’.
Langdon’s counter-explanations for this group of traits are quite diverse. For example, the enlarged pharynx is
explained by speech (Langdon 1997:482), the nose and paranasal sinuses by climate (Langdon 1997:482), and “the
origin of voluntary control of human breathing is to be found in bipedalism” (Langdon 1997:481.)
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These explanations are not impossible but Langdon does not provide any argument as to why the non-AAH
explanations are better than those invoking some selection from increased swimming and diving in human ancestry,
or how several different explanations can be more parsimonious than a single common one.
The other traits listed were ‘diving reflex’, ‘direction of hair follicles’, ‘sexual dimorphism of scalp hair’, ‘activity
of sebaceous glands’, ‘paucity of apocrine glands’, eccrine sweating’, ‘absence of “salt hunger”’, ‘vaginal depth’,
‘hymen’, ‘frontal sex’, ‘loss of oestrus’, breasts’, ‘tears’, ‘large brains’, ‘webbed digits’, ‘neoteny’ and ‘tool use’.
For each, Langdon used the same technique: Describe the aquatic argument in one or two sentences and then
dismiss it just as quickly. Considering that Morgan had written five books on the subject, each usually with a whole
chapter dedicated to a cluster of such traits, Langdon’s attempted rebuttal could be seen as being rather simplistic.
The latest, and arguably the best, of those books (Morgan 1997), as mentioned earlier, was published too late to be
included in Langdon’s critique. Several of the criticisms Langdon made of arguments in favour of an aquatic
explanation for these traits were addressed in this work.
For example, a few were retracted: For instance the claim that “the employment of eccrine glands over the entire
body for evaporative cooling is unique to humans” (Langdon 1997:484) and that it was adaptive to salt excretion
was openly withdrawn (Morgan 1997:116-117) after the publication of evidence showing eccrine sweat cooling in
patas monkey (Erythrocebus patas) (Mahoney 1980, Elizondro 1988).
Others were enhanced: The aquatic explanation for the descended larynx was treated with a full chapter (Morgan
1997:123-136) and Langdon’s claim that Morgan “all but ignores” observations between the relationship between
the pharynx and speech can be countered by the fact that Morgan wrote a whole chapter on this too (Morgan 1997:
137-148).
Overall, Langdon’s presentation of the list of traits may leave someone sceptical of the hypothesis shaking their
head in disbelief at the diversity of the claims made in support of this idea.
But behind the parody lies a serious point: If hominins had become adapted to a water-side habitat then isn’t this
exactly what one would predict? That a whole cluster of relatively small human traits would be indicative of a more
aquatic past? It should also be remembered that even Langdon considered eleven out of the twenty-six traits, the
most important eleven from an AAH proponent’s point of view, either “possible aquatic adaptations” or “consistent
with the AAH” Langdon (1997:488.)
Perhaps a more serious approach would have been to look at the broad generality of the AAH claim: that humans
show indications of past adaptation to the waterside which our ape cousins lack. This should, if true, translate into
features which result in better locomotion (wading, swimming, diving) through water and a greater physiological
dependence on it.
Although apes do appear to wade bipedally rather successfully, there is little evidence that they are as strong
swimmers or divers as humans. Physically, they are not as buoyant as humans (Angus 1971) and zoos have
traditionally used moats to keep great apes inside their enclosures. Whereas the river Congo has, apparently, been a
successful enough barrier preventing chimpanzees and gorillas co-habiting with bonobos in significant numbers for
at least two million years (Gagneux et al. 1999), far larger bodies of water have not constrained human expansion
(Morwood et al. 1998.) To the knowledge of the author there is only one piece of anecdotal evidence in the
literature of a single male chimpanzee reportedly swimming at Conkuoati, Republic of Congo for a matter of a few
metres (Attenborough 2002:297) whereas there are many such reports of chimpanzees being very reluctant to move
into water and even drowning as a result of doing so (see, e.g. Angus 1971).
Perhaps, then, one of the clearest indications that human ancestors had a more aquatic past than our ape cousins is
the marked disparity between the swimming abilities of humans and our nearest cousins. Indeed it is difficult to
imagine any other comparison of the relative abilities of two species in any given media, where such a clear
differential in abilities there, would not automatically lead a biologist to the conclusion that the discrepancy was
explained by natural selection. This difference was, however, overlooked in Langdon’s critique.
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General critique of the evidence
Having categorised the twenty-six traits into the six groupings described earlier, Langdon does go on to make some
rather strong counter arguments to the AAH. To begin with he outlines ‘two inconsistencies’ which undermine the
hypothesis.
“The first is the contradictory evidence regarding marine or fresh-water habitat” (Langdon 1997:488.) Langdon
correctly recognises the discrepancy in arguments that invoke marine habitats, e.g. lack of ‘salt hunger’ and copious
salt loss through sweating and those that invoke fresh water habitats, e.g. human dependence on fresh water and
infant intolerance to salt.
This is a good counter argument and requires a sophisticated response. As Langdon argues later himself, some
explanations may require more work to understand than others and just because an explanation is not simple it does
not make it wrong. One possible solution to this objection within the AAH framework is outlined in the last section
of this paper.
Langdon’s second problem, regarding “the extent of the specialization for aquatic life experienced by our
ancestors” (Langdon 1997:489), is easier to deflect. He alludes to the very issue of the problem of interpretation of
the hypothesis discussed earlier by arguing that “the greater the hypothesized specialisation, the more improbable
the rapid return to land.” Moreover, that many other traits which might reasonably be expected to be present if had
become adapted to an aquatic way of life (such as streamlining of the torso and repositioning of the nostrils) are not
present in humans. But this assumes that the AAH is proposing a singular, distinct aquatic ‘phase’ followed by the
“return to the land”. If one simply modifies this part of the model to suggest, instead, that our ancestors always
lived in waterside habitats, (or that our ancestors were subject to a greater number of ‘more aquatic’ pieces in a
mosaic of evolutionary steps than were the apes) this objection of Langdon’s could be removed.
Time, place and the fossil record
Langdon states “whatever difficulties emerge, the AAH is unlikely ever to be disproven on the basis of comparative
anatomy. One body of data that potentially can disprove it is the fossil record” and that “the problems of
reconciling it [the AAH] to the fossil record have increased over the years” (Langdon 1997:489).
This view would, again, appear to be based upon the premise that the AAH is arguing for a singular and ‘full-on’
‘aquatic phase’. These are aspects of the hypothesis, it is true, which both Hardy and Morgan both explicitly did
suggest but which, as we shall see shortly, is not actually necessary for some variations on the AAH. Indeed, even
if they got this part of the model wrong, it does not mean that the whole hypothesis must be rejected.
Langdon correctly criticises Morgan for claiming that “Australopithecus was the ape that returned to the land”
(Morgan 1982:116) as this view (that the putative aquatic ‘phase’ had preceded Australopithecus) would imply that
all the traits used to support it in humans would also still be present in australopithecines in greater degrees, and he
makes a good case that this would appear to be very unlikely.
He states “the fossil record might appear less problematic if the evolution of aquatic adaptations were understood to
continue through to the early stages of genus Homo, at least to 2.0 million years ago” but argues that even then, the
association of later hominid [hominin] fossil sites with “water, on lake shores, streams and river channels, or caves”
(Langdon 1997:490) is probably merely due to taphonomic factors.
The taphonomy argument is one that is often used to contradict assertions that the fossil record, if anything,
promotes the view that human evolution was influenced by water more than apes (after all, fossils of thousands of
individual hominins, i.e. specifically human ancestors, have been found in depositional substrates, but absolutely
none are currently specifically attributed to Pan or Gorilla ancestors.) But even this argument can be seen as some
kind of special pleading. Consider just two examples: The paleoecology of the area around the Hadar site, where
AL 288-1 (“Lucy”) was discovered, was clearly dominated by lakes, streams and swamp wetlands for some 1.4
million years (Johanson & Edey 1981:129); Similarly, the paleo-ecology of the site of WT 15000 (‘Nariakotome
Boy’) appears to have been a flood plain wetland habitat that was up to 60km wide according to Feibel & Brown
(1993:37.)
8
If we ignore those factors, or assume that the AAH was proposing a purely coastal habitat, then it could be argued
that Langdon does make a good case for dismissing the AAH on the grounds of fossil evidence if the AAH is taken
as the hypothesis that human ancestors went through a singular and distinct aquatic phase before the origin of the
genus Homo. But, as with the ‘improbability of a return to land’ argument just covered, this objection can easily be
met with a simple substitution of the model’s assumed singular, more aquatic ‘phase’ with a generally water-side
habitat and/or a greater number of ‘more aquatic’ pieces in a mosaic of evolutionary steps in human evolution than
the apes.
Moreover, much of the evidence emerging since the time of Langdon’s paper has added weight to the notion that
many early hominins (and some hominids which are not unequivocally placed as ancestral to Homo) did actually
specifically live in wetter habitats than we might have assumed. According to Reed (1997:289) “reconstructed
habitats show that Australopithecus species existed in fairly wooded, well-watered regions.” WoldeGabriel et al.
(2001) showed “that these earliest hominids derive from relatively wet and wooded environments.” None of the
latest fossil findings of Sahelanthropus tchadensis, Orrorin tugenensis, Kenyanthropus platyops, Ardipithecus
ramidus and Australopithecus anamensis contradict this water-side model for early hominids. Indeed the TorosMenalla site where Sahelanthropus tchadensis was found, was actually inside the maximum extent of the Holocene
‘Mega Lake Chad’ and contained a significantly high percentage of aquatic and semi-aquatic fauna (Vignaud et al
2003.)
As Langdon himself concedes (Langdon 1997:490), later Homo fossil sites are almost always associated with
water. Although this might be due to taphonomic bias and many of these sites have significant faunal assemblages
from more open grassland species this hardly amounts to a refutation that water could have acted as an agent of
selection in late human evolution. Fossil sites of gallery forest habitats, prone as they are to both flooding and
desiccation, are likely to be comprised of faunal mixtures of aquatic, arboreal and open grassland species. Such
mixtures do appear to be typical of hominin site assemblages. (see, e.g. Vignaud et al 2002; Frost & Delson 2002;
Harris & Leakey 1993). The presence of equuid fossils at such sites is no more indicative of a predisposition to life
on the open plains, as the presence of a crocodilian is to life in the water.
Stringer & McKie (1997) and other proponents of a recent Out of Africa exodus have argued that coastal migration
routes have played a significant part in the evolution of fully modern Homo sapiens, thus clearly placing them in a
more aquatic habitat than those typically associated with the great apes. That those people relied on coastal
foraging is clearly evidenced by unequivocal evidence of shell middens. (e.g. Walter et al 2000). Finally, one of the
most significant and possibly the earliest (at between 154 and 160 kya) modern Homo sapiens finds has recently,
unambiguously placed them not only next to water sources but also reliant on aquatic food sources when they noted
that “associated faunal remains indicate repeated, systematic butchery of hippopotamus carcasses” (Clark et al.
2003:748).
Langdon’s concluding remarks on the fossil record, that “subsequent years have made the fossil record much more
complete and less compatible with the aquatic hypothesis” would, therefore, seem out of date and potentially quite
misleading.
Umbrella hypotheses and the problem of parsimony
In his final section, Langdon takes a more general line against hypotheses which attempt to explain a whole group
of features in one fell swoop.
Langdon’s first point ‘False comparisons’ criticises Morgan for holding up the aquatic ape hypothesis against a
competing “savannah theory” which, he claims, is “a straw man” created by her for that purpose. He states: “The
savannah hypothesis that Morgan criticizes turns out to be a straw man”, arguing that many in the field “are now
discarding the savannah setting for hominid divergence” (Langdon 1997:490). This may be correct but it is clearly
equally true that many paleoanthropologists have published work (e.g. Rodman & McHenry 1980, Lovejoy 1981,
Wheeler 1984, 1991, 1992, Vrba 1985, Hunt 1994) before Langdon’s critique, and before Morgan’s latest books,
which are very much based on the model that aridity and a greater adaptation to more open and grassy habitats was
a significant driver of hominin evolution. Indeed Tobias is quite open about agreeing with Morgan on this point. He
wrote “Until recently, the evolution of early hominids [hominins] in the savannah has been a strongly held,
prevailing hypothesis” (Tobias 2002:15) and “the competing [with the AAH] hypothesis is no longer tenable since I
9
presented much evidence against it in my Daryll Forde Lecture at University College London in 1995” (Tobias
2002:16).
Even though it appears to be the case that since Langdon’s critique fewer papers have been published arguing
explicitly for a savannah setting for hominin evolution than before, the general consensus still appears to be that it
was the gradual aridification of Africa since the Miocene that was the main ecological factor that drove the process
of hominization. (See, e.g., Leonard 2003, Oppenheimer 2004:1-14; Stanford 2003:138; Wynn 2004:116.) Indeed it
is difficult to think a single text on human evolution that does not allude to ‘more open habitats’ (if not the term
savannah directly) somewhere, as a major factor in the story of human evolution. As Morgan eloquently put it: “It
has been repeatedly asserted (for example on the internet) that there was never such a thing as the ‘savannah
theory'’ that it was simply a straw man constructed by Elaine Morgan for the pleasure of knocking it down again,
and that no reputable scientist can be shown ever to have used the phrase ‘savannah theory’. The last part of that
statement is true. I would no more have expected them to use that phrase that I would expect a Creationist to refer
to ‘the God theory’- their faith in it was too strong for that.” Morgan (1997:14).
Morgan’s point about the ‘savannah theory’ is simply that humans are so substantially different from our ape
cousins, considering how closely related we are, “that something must have happenedto our ancestors which did
not happen to the ancestors of the other apes” (Morgan 1997:13) and that the savannah therefore at least offers a
radical enough change in habitat to potentially explain those differences`. Langdon’s counter-argument, that it was
not savannah but “a woodland or mosaic setting” (Langdon 1997:490) posits human evolution to have occurred in a
habitat so similar to that of extant chimpanzees and gorillas that it is no longer clear how such a divergence in
physical traits could have resulted.
However, whether the savannah theory is ‘dead’ or not, anyone accusing the AAH of using ‘straw man’ arguments
should be very careful not to be found guilty of doing the same thing themselves in trying to discredit it. By only
emphasising comparisons with fully aquatic marine mammals and avoiding areas of discussion which invoke
human ancestors as being merely more exposed to water as an agent of selection than our ape cousins Langdon, and
other ‘aquasceptics,’ are open to accusations of using the same straw man tactics themselves. The use of such
strategies on either side can only act to polarise the debate and not bring us any closer to finding a solution to the
problem.
Langdon’s next point, headed ‘Parsimony’, attempts to refute the AAH’s claim to greater parsimony in explaining a
cluster of human traits in one go. He provides four reasons for this:
Firstly, he argues that the AAH explains certain human traits “without predicting them”. Specifically, he questioned
why “with such diverse examples of seals, otters, manatees, and porpoises before us, one must explain why
observed human traits and not others were selected.” (This point was actually almost the same as his third that we
“should consider not only observed phenomena, but also unobserved possibilities”) This point demonstrates, once
again, that Langdon is taking for granted the extreme (rather than the mild) form of hypothesis. More aquatic does
not mean “aquatic”. His first section was entitled ‘false comparisons’ and yet here, in his second, he starts by
making a fundamental false comparison himself.
Answering that criticism, and taking the AAH’s basic assumption, that hominin ancestors lived in water-side
habitats more than did the ancestors of apes, one could make three broad predictions: That more hominin fossils
would be found in riverine/lacustrine/coastal deposits than ape fossils; That humans would be better able to move
through water (wade, swim and dive) than apes are and have a set of traits which helped in that regard; And, that
humans would be more physiologically dependent on water than apes. Those predictions need testing thoroughly
but would appear, at first glance, to hold true.
His second argument is less clear. He appears to argue that because explanations for individual traits are not free
from conjecture, then grouping them under an umbrella together with other explanations does not make them more
parsimonious. This seems to contradict the definition of the word ‘parsimony’. Of course there is a great deal of
conjecture about each and every trait but if, for example, all twenty-six Langdon listed could be explained by one
single hypothesis – an adaptation to water-side life, then that must be a more parsimonious solution than invoking
twenty-six separate explanations.
Finally, his fourth reason is a logical one: That postulating hominins moved from a terrestrial to a marine habitat
and then back again is less parsimonious than “the assumption that a lineage that was terrestrial in the Middle
Miocene and terrestrial in the Middle Pliocene was terrestrial in the intervening time.” (Langdon 1997: 491). He
10
argues that it is the “unnecessary complication of the narrative that has led many anthropologists to reject the
hypothesis out of hand.”
However, even this objection could be withdrawn if one understood the AAH to posit, not a diversion to an aquatic
phase and back again as such, but as a general, constant pattern of hominins living in water-side habitats more than
their ape cousins did. It is an objection, in any case, which Langdon contradicts himself in the next section when he
argues that human evolution probably involved a very complex mosaic of steps, far more complex than the
Hardy/Morgan putative ‘aquatic phase’ and subsequent ‘return to land’.
In that next section, ‘Mosaic evolution revisited’, Langdon argues that as the hominid fossil record demonstrates
that key traits appear at different times they probably appear for different reasons. Furthermore, as several hominids
existed contemporaneously, he suggests that hominid evolution is not one story but many different ones. Langdon
argues that is unlikely that all of this (multiple evolutionary steps in multiple evolutionary lineages) is unlikely to
be explained by a single factor.
This is almost certainly true. In fact the ‘real truth’ of human evolution is, in all likelihood, far more complex than
we can possibly imagine. It probably involved a bewildering mosaic of different stages, some happening in
sequence, some in parallel, along different contemporaneous lines, as he suggests. Bipedalism certainly appears to
have evolved much earlier than other characteristics of human-ape divergence. But what Langdon fails to
demonstrate at this, or at any, point in his review, is why some parts of that mosaic could not have involved periods
of evolution where some apes were exposed to water as an agent of selection more than others.
Finally, Langdon completes his refutation of the AAH by drawing analogies with creationism and explanations
which include invoking aliens from space. It is, like them, “only one of several ideas rejected by orthodox science
that has refused to go away” he writes (Langdon 1997: 492).
Langdon provides several properties which the AAH, he argues, has in common with such theories in a section
entitled ‘The appeal of unorthodox theories’.
First, he suggests, that such theories offer “absolute answers that may not be available from orthodox science.”
Langdon makes no mention that the title of Hardy’s (1960) paper was merely a question and his article ended: “My
thesis is, of course, only a speculation – an hypothesis to be discussed and tested against further lines of evidence.
Such ideas are useful only if they stimulate fresh inquiries which may bring us nearer the truth.” Nor does this give
a fair portrayal of Morgan’s work, which very much followed in Hardy’s modest footsteps. It can hardly be claimed
that Morgan tried to provide absolute answers, merely to question those answers provided by others. Indeed, the
fact that Morgan has modified and retracted various arguments over the years (e.g. Morgan 1997: pp 116-117)
indicates that she is one proponent of the AAH who is open to contradictory evidence.
Secondly, Langdon compares the AAH with heterodox ideas which feed on suspicion against the scientific
establishment but fails to mention that it’s core proponent, Sir Alister Hardy, was a Fellow of the Royal Society: a
body that in 1960, at least, was the very elite of the scientific establishment and that another such fellow, Phillip V.
Tobias, has recently called for his peers to be more open to the hypothesis. As well as the supporting comments
published in the 2002 paper cited earlier, Tobias also said in a 1998 documentary interview “I see Elaine Morgan,
through her series of superbly written books, presenting a challenge to the scientists to take an interest in this thing,
to look at the evidence dispassionately. Not to avert your gaze as though it were something you that you hadn't
ought to hear about or hadn't ought to see. And those that are honest with themselves are going to dispassionately
examine the evidence. We've got to if we are going to be true to our calling as scientists” (Tobias 1998b).
Langdon’s evidence for his claim that the AAH feeds on suspicion against the establishment was merely that
Morgan has consistently compared the poor reception of the aquatic ape hypothesis with the early sceptical
reception of the continental drift theory of Wegener, a historical fact that no-one would dispute today.
His third property, which sounds very much like his second, was that “there is a special appeal for peripheral
segments of the population in rejecting the authority that science and academia represent.” The evidence for this
claim was that Elaine’s first book, written over twenty-five years earlier, “spoke with the passion of embittered and
victimised feminism” (Langdon 1997:493). Many would say “and good for her that she did” because that book was
a major, early contribution to the feminist movement which has helped improve the lives of millions of women in
the years since. Langdon fails to credit Morgan with the fact that her following books were very carefully written
so to not provoke such reactionary criticism.
11
Fourthly, Langdon suggests that the AAH is popular because it is easily communicated “in simple narrative” to
those “not actively engaged in the primary evidence” (Langdon 1997:493). Putting aside the question of whether
the AAH is popular or not (how many school books on the subject of human evolution show pictures of early man
as ‘man-the-mighty-hunter’ on open, grassy plains rather than images of women bathing infants in water?) it is not
clear that this argument uniquely applies to the AAH. In the same way, the so-called savannah hypothesis probably
became popular in the 1960s because it ‘made sense’ from the view of man’s ancestry prevalent at the time: another
umbrella hypothesis. If the AAH does become popular because it explains many human traits through a simple
narrative, it should hardly be used as an argument against it.
Fifthly, Langdon compares the AAH’s “great emphasis on negative arguments” (Langdon 1997: 493) with that of
creationism, suggesting that Morgan places “a great deal of weight on the tentativeness of hypotheses in the
terrestrial models” (Langdon 1997: 493) as creationists do with their perceived insufficiency of evolutionary
theory. This is a rather remarkable argument to make considering that most of her work is full of positive ideas,
attempting to explain traits that university level texts on human evolution have often avoided completely. To
compare the AAH with creationism is particularly facile as the hypothesis has, at it’s core, fundamental neoDarwinist adaptationism, the argument that every human trait must have an adaptive explanation rooted in natural
selection.
Langdon’s final point, which sounds very much like his fourth, is that “unorthodox models are especially
successful when consensus views are not easily communicated to the public” (Langdon 1997:493). He makes the
point by comparing two explanations for human breath control. He argues that explaining that “we can hold our
breath because we are adapted for diving” is a simple statement to hear but that “we can hold our breath because
respiration is independent of locomotion in a biped” requires more understanding.
This argument is rather simplistic in itself (some quadrupeds, e.g. otters, have excellent breath control, whereas
some bipeds, e.g. turkeys, do not) and also a highly selective one. Where the AAH is difficult, for example when
coming up with a plausible timescale, then the ‘simplicity’ of the orthodox interpretation of the fossil record is
cited. Where the AAH is simple, perhaps arguing that human bipedality, nakedness, subcutaneous fat and breathing
control are all explained by an adaptation to water-side living, then the counter-argument is that it is too simple.
Then, Langdon encourages us, instead, to “look for complex stories with weak plots” (Langdon 1997:493). In
Langdon’s view, it seems, the AAH just cannot win. He ends with a charming analogy of proponents of such
umbrella hypotheses acting like drunks “looking for lost keys not where they lost them, but where the light is best”
(Langdon 1997:493).
On top of all of these detailed flaws in Langdon’s arguments, yet one more must be added. Perhaps the greatest
weakness of this critique of the AAH was the fact that it all but ignored the findings of the Valkenberg symposium,
published six years earlier. Langdon did know about it (he wrote “The AAH was the subject of a published
symposium that represented both favourable and opposing views.” Langdon 1997:480,) but then failed to cite a
single comment or piece of data from any of the twenty-two contributions.
The four editors of the publication were given the unenviable task to trying to summarise the symposium, and to
produce some kind of concluding statement on the merits of the AAH. Overall, they decided against the AAH but,
as with Langdon, it should be clearly understood what it was they thought were rejecting: They wrote (Roede et al
1991:342) “it is clearly impossible to provide a conclusive answer to the question of whether there was an aquatic
ape...” [my emphasis] but that “... Our general conclusion is that, while their are a number of arguments favouring
the AAT, they are not sufficiently convincing to counteract the arguments against it.” They did further suggest that
‘it may well be rewarding to reconsider the issue once further evidence - for instance from palaeontology - becomes
available.’ (Roede et al 1991:342.)
Of the four editors, it should also be noted, that Jan Wind wrote a piece against the AAH, Machteld Roede herself
wrote one in favour and the other two, John Patrick and Vernon Reynolds, wrote papers somewhere in between. It
might, then, be enlightening to note the type of arguments used by Patrick and Reynolds as they must have, in the
end, come down against the hypothesis.
Patrick wrote in his summary on ‘Human Respiratory Adaptations for Swimming and Diving’: “No conclusive
evidence is available to link the respiratory characteristics of modern Homo with those that might have provided
selective advantages to earlier hominids [hominins] living in an aquatic habitat. However, the ability to control
breathing from the cerebral cortex rather than from the brain stem could be regarded as a respiratory adaptation
12
suiting hominids [hominins] to life in shallow water.” (Roede et al 1991 p236.) And Vernon Reynolds’ summary
of the symposium, included the opening paragraph used in this paper, was arguing most clearly that he though there
was evidence that water may have acted as an agency of selection in human evolution.
It would appear that Roede et al’s (1991) review, like Langdon’s critique six years later, was considering the idea
that there was actually an ‘aquatic ape.’ If the AAH is defined more moderately and possibly more in tune with
what Hardy originally argued, that man was merely more aquatic in the past, then it would appear, from the
arguments in their papers, that at least three out of four editors were clearly endorsing that view.
This, certainly was the impression of Colin Groves. In his book review of Roede et al (Groves 1993) he also picked
out some of the same words in Vernon Reynolds’ statement this paper begins with. Considering those words: “Not
only did they take to water from time to time but . . . the water . . . was a habitat that provided enough extra food to
count as an agency for selection” (Reynolds 1991:340), Groves commented “Is this, perhaps, all that was necessary
all along? Might Hardy and Morgan have seen their ideas discussed if they had taken then just this far? I suspect it
might” Groves (1993:1040).
But Roede et al (1991) is not the work in question here, it is Langdon’s. Suffice it to say that by choosing not to
draw on that body of work only makes the power of his refutation that much weaker. If an undergraduate student
had submitted an essay on the AAH and not significantly drawn upon Roede et al (1991) his/her tutor might have
been justified in putting a red line through it and asking for it to be re-written. Yet Langdon’s paper was peer
reviewed, made it into the esteemed pages of the Journal of Human Evolution and remains today the unchallenged
refutation of the Aquatic Ape Hypothesis.
It is argued here that whatever view is held on the so-called aquatic ape hypothesis, Langdon’s critique falls well
short of any kind of valid rebuttal. His use of false comparisons with true aquatic mammals at almost every
juncture demonstrates that, like many in the field, he assumed an extreme (rather than a mild) interpretation of what
the hypothesis was proposing. Perhaps the cause of this misunderstanding lies with Hardy and Morgan, perhaps
not. But it would appear to be rather clear that if this issue is ever going to be resolved one way or the other, people
supportive or critical of the hypothesis should, at least, agree to a basic understanding on what it is they are arguing
about. Seven years after Langdon’s attempt at a rebuttal, perhaps it is time such a working definition was actually
published.
The AAH... Now
The AAH as it was perceived by Langdon in 1997 is not the same as it is today. Like any model of human
evolution, it evolves in response to criticism and new emerging evidence. Even in 1997, it was wrong to assume
that there was only one aquatic model. As Langdon accused Morgan of creating a monolithic straw doll, a
caricature that all opponents of the aquatic hypothesis believed in the ‘savannah theory’, the same accusation can
be made to him in choosing to critique only Morgan’s work.
Langdon gave little or no reference to the work of Ellis, Verhaegen, Crawford and others who, even before 1997,
had already began to formulate alternative aquatic-based models of human evolution which met several of the
objections laid out in his paper. A brief review of some of those ideas now follows.
Ellis’ Ecological Argument for a ‘Wetland Ape’
In a series of papers published in the late 1980s and early 1990s, Derek Ellis promoted a moderate version of the
AAH based on an ecological hypothesis that wetland habitats could have been populated by apes leading to their
adaptation to a more water-related lifestyle (Ellis 1986, 1987, 1991, 1993).
The hypothesis rests on the argument that if hominins moved out from woodland into more open habitats “they
were not moving to an environment where there was less, or no competition. The baboon was a highly successful
savannah species already well adapted to a grassland environment…” (Ellis 1993:209). In addition to the baboon
there were “also fierce, fast predators on the grasslands, and limited protection from them for a slow biped,
especially from the predators that hunted at night” (Ellis 1993:209).
Ellis argues that if savannah habitats would have been relatively barren and harsh for a hominin newcomer, wetland
habitats, by contrast, would have been relatively food rich (especially in the high energy foods postulated for large
13
brain growth) and safe from predators. He writes “some shift away from a diet of foliage would have been imposed
on a savannah ape, but on the grasslands animal-food replacements would have been scarce, elusive, and hotly
contended for. Baboons have not managed it. The initial incorporation of animal food into the diet would be very
much easier via the tropical marine food chain, where the supply of seafood was plentiful and available all year
round, and gathering it called for no skill, incurred little danger, and encountered no serious competition” (Ellis
1993:212).
It should be noted that Ellis’ hypothesis completely negates several of Langdon’s objections, such as the lack of
fossil evidence for a distinct, and probably coastal, singular, ‘full-on’ aquatic phase.
The ‘aquarboreal’ (wading-climbing) ape model
Similarly, unlike Hardy and Morgan, who did postulate that some ape taxa did experience such a definite ‘phase’
when they were exposed to a water-side habitat before returning to a fully terrestrial existence, Verhaegen et al.
(e.g. 2002) also propose a very different scenario.
For the commencement of greater exposure to water, they propose that it actually happenedbefore the Pan-Homo
split and even before the Gorilla-Homo split.
According to their model, all African great apes and Homo evolved from a common ancestor that was already a
wading-climbing ape. They hypothesise that such apes might have inhabited coastal forests and would have, in
particular, have thrived possibly in the coasts along the Tethys / Mediterranean and Red seas in the Mid and/or
Late-Miocene epoch.
They argue that “a combination of fossil (including the newly discovered Orrorin, Ardipithecus and Kenyanthropus
hominids) and comparative data now provides evidence showing that: (1) the earliest hominids waded and climbed
in swampy or coastal forests in Africa–Arabia and fed partly on hard-shelled fruits and molluscs; (2) their
australopith descendants in Africa had a comparable locomotion but generally preferred a diet including wetland
plants; and (3) the Homo descendants migrated to or remained near the Indian Ocean coasts, lost most climbing
abilities, and exploited waterside resources.” Verhaegen et al. (2002).
The model predicts that Gorilla and, somewhat later, Pan were off-shoots from this coastal inhabiting swamp ape
that migrated inland, up river systems and eventually, as Africa became drier, began to adopt more terrestrial lives
and a quadrupedal form of locomotion. Homo, meanwhile, stayed on or returned to the coasts but eventually began
to inhabit less forested coastal areas. Verhaegen et al. predict that from this hominin stock Homo populations
evolved to become coastal omnivores partly relying on marine food sources as they migrated along the Indian
Ocean and Mediterranean coastlines.
More recently Verhaegen has argued (personal communication) that the AAH should actually be split into two
separate aquatic ape theories (AATs). One, he terms the ‘Aquarboreal Ape Theory’, is more or less the earliest
phase of the model outlined above. The second, termed ‘Amphibious Ancestors Theory’, deals more with the other
human traits such as nakedness and sub-cutaneous fat, postulating that they arose from exploiting food resources in
coastal habitats predominantly from swimming and diving during the first (Homo erectus) ‘Out of Africa’ diaspora.
Marsh-Crawford Brain Growth Model
Crawford and Marsh (1989) outlined a very wide ranging model for how the evolution of life itself happened on
earth, stressing the importance of food as a driver at every stage and for every form of life, including human
evolution. Specifically, they argue that the large human brain has been able to evolve only as a result of a change in
diet of human ancestors to those from the marine food chain, which are rich in omega-3 essential fatty acids. These
fatty acids are strongly implicated in the development of brain tissue (Broadhurst et al. 2002). Crawford and Marsh
promote a moderate level of aquaticism in their work, arguing that hominins “most probably evolved at the landwater interface.” (Crawford & Marsh 1989:163).
14
Fresh-water ‘River Ape’ Model
It is the view of the author that all the existing models of human evolution, whether AAH-based or more orthodox
in their leanings make some contribution to understanding human evolution but are deficient in some way or other.
It is argued that what may be required, is some kind of a hybrid of models based upon the orthodox paradigm, but
which combines the best of the original Hardy/Morgan ideas with the strengths of those of Ellis, Crawford and
Verhaegen et al. whilst simultaneously addressing as many of Langdon’s and others’ objections to the AAH.
A basic outline of what would be included in this hybrid of models is provided below:

The most significant event in the early evolution of hominins is their bipedality. As extant African great
apes appear to be at their most bipedal in shallow water (Kuliukas 2002) and as arm-hanging or suspensory
primates appear to move bipedally when on the ground (see, e.g. Hirasaki et al 2000) it is argued that some
wading-climbing model not unlike that of Verhaegen et al. (2000) provides a case for some sort of shortlegged, partial bipedalism at least in African hominoids. This argues that the, as yet undetermined, last
common ancestor of Gorilla, Pan and Homo was a rather unspecialised swamp forest (coastal or inland,
unspecified) ape that exhibited facultative bipedalism whilst in water but was also a very competent
suspensory climber. It is argued that this is a logical precursor to both fully terrestrial bipedalism (in Homo)
and to quadrupedal knuckle-walking (in Pan/Gorilla). This is consistent with the recent early hominid finds
of Sahelanthropus tchadensis and Orrorin tugenensis which may even predate the last common ancestor of
Pan and Homo if molecular clock dates of 5-7 Ma are taken .

In the Late Miocene/Early Pliocene, the aridification of Africa, particularly the region east of the rift would
have caused the forested habitats to shrink not in a random, patchy way, but rather systematically, closer to
sources of water. This next phase of hominin evolution, then, is postulated, to have happened in strips of
riparian forests along extensive rivers and lakes of East Africa as promoted, albeit for a very different
model, by Kingdon (2003). Once again, here is an environment where the hominins would be likely to
move through water more than they had before and more than their cousins which still lived
contemporaneously in dense western tropical forests. The model postulates that during this phase the
ancestors of humans increasingly moved bipedally even in shallow water and even on dry land, thus
perfecting their bipedality, whilst the ancestors of African great apes adopted knuckle-walking as a postwading-climbing form of terrestrial locomotion.

The next broad phase of this model suggests that, later, some early forms of Homo migrated to coastal
regions, finally abandoning their arboreal ancestry and becoming more adapted to swimming and diving for
food. This might have been through loss of habitat after further aridification or through competition for
food. It is argued that this hominin, Homo erectus (sensu lato) became very successful in exploiting these
and, subsequently, a variety of other niches and food supplies, accounting for its diaspora across Africa and
Eurasia, as far as Java from around 2 mya.

Finally, the model proposes that a radical novel change in the human genotype caused the speciation of
fully modern Homo sapiens in East Africa around 250 kya. This change may have been some kind of
mutation leading to a gross neural change, as espoused by Richard Klein (1999:515) or, as favoured by this
author, a hybridization event of two hominin groups separated for between one and three million years,
possibly around the Danakil depression after the inland sea there started to desiccate. Such a reticulation
event could account for the change in the number of human chromosomes, from 48 to 46, which would
effectively isolate the nascent species genetically from its parental groups and account for some of the
rather saltatory changes in our evolution (e.g. rapid brain growth, full syntactic speech and culture). After
the speciation, probably in Africa, it is proposed that fully modern Homo sapiens was uniquely equipped to
expand and ultimately replace all other hominins on the planet, in accord with the Out of Africa
replacement model of human evolution (e.g. Stringer & McKie 1997). It is suggested that this part of the
model might explain the somewhat contradictory AAH arguments Langdon cited, and mentioned earlier,
about human supposed adaptations to both fresh and salt water. If one of Homo sapiens’ parental species
was fresh water adapted and the other more salt water adapted, the contradictory nature of these traits
might be better understood.
Clearly, as Langdon has shown, if the AAH is interpreted in an exaggerated form, it has a number of flaws.
However we have seen that this interpretation is not the only one. Verhaegen et al.’s ‘aquarboreal’ model is a clear,
15
alternative, water-side-based model of human evolution which avoids some of Langdon’s criticisms but attracts
other new ones. Ellis’ ecological arguments for a wetland ape are very strong, and Crawford et al. have shown that
marine and lakeside food chains may well have been the only ones suitably rich for the large human brain to have
evolved. It is clearly possible to interpret the hypothesis in a much milder form without, it is argued, losing any of
its explanatory power.
In fact, it is argued that if one finds a kind of a synthesis of the orthodox and AAH paradigms, an explanatory
synergy arises. The orthodox view, that the gradual aridification of Africa since the Miocene has been the main
ecological driver of human evolution, may actually be correct but perhaps it is the assumption of the consequence
of that change that needs reconsidering. Rather than the notion that human ancestors were being forced into a
general move into more open habitats, the resulting factor that drove the process of hominization could have been,
paradoxically, the adoption of habitats ever closer to reliable sources of water and its rich food supply. Flooddesiccation cycles in ever greater phase-shift and frequency (Potts 1998) would only increase the exposure of our
ancestors to moving through water.
The study of human evolution is very much subject to interpretation of evidence and open to speculation but the
part that water played in that evolution appears to have been overlooked. Tobias (2002:16) calls “for the heavy,
earth-bound view of hominid [hominin] evolution to be lightened and leavened by a greater emphasis upon the role
of water and waterways in hominid [hominin] development, survival, diversification and dissemination.” This
paper is an attempt to respond to that plea. It is claimed here that there is actually no significant contradiction
between the existing paradigm of human origins and those espousing a greater role for water if one merely
emphasises more the importance of fresh water sources such as inland rivers and lakes.
The AAH – A Definition
This document will end as Langdon’s, it is argued, should have started: with a simple, unambiguous
definition of what the aquatic ape hypothesis actually is. The working definition below is taken as the
lowest common denominator of all the aquatic models discussed here. It has been endorsed by Morgan
(personal comment 2004) and so, it is proposed, that some form of this definition should be used in future
assessments of the plausibility of the model.
It should be noted that this is a simple, overarching definition for what is a very broad hypothesis. It may,
therefore, be criticised for being too vague to make falsifiable predictions. To counter that objection, it is
argued that each proposed physical difference explained by greater selection from moving through water,
such as bipedalism, body hair reduction, increased adipocity, would have its own sub-hypothesis, each
with its own clear and falsifiable predictions (four are outlined below). It is argued, contrary to one of
Langdon’s major claims, that every AAH sub-hypothesis thus gains in strength from each other as it must
be more parsimonious to explain all of them with one plausible scenario than to inoke several different
ones.
The Aquatic Ape Hypothesis (AAH):
The hypothesis that moving through water has acted as an agent of selection in the evolution of humans
more than it has in the evolution of our ape cousins. And that, as a result, many of the major physical
differences between humans and the other apes may be best explained as adaptations to moving (e.g.
wading, swimming and/or diving) better through various aquatic media and from greater feeding on
resources that might be procured from such habitats.
Falsifiable Sub-hypotheses:
1. The Hominid Bipedalism from Wading Hypothesis:
The hypothesis that wading through shallow water was a major component of the locomotor repertoire of the
earliest proto-hominid bipeds.
16
Falsifiable Predictions:
1. That extant apes should be most predictably bipedal in shallow water than in other substrates.
2. That the paleohabitats of the earliest bipeds were places where significant wading locomotion would have
been beneficial.
3. That the differences between the postcranial anatomy of the earliest bipedal hominids and modern humans,
as evidenced by the fossil record, should be consistent with specific adaptations for wading.
2. The Nakedness for Drag Reduction Hypothesis:
The hypothesis that selection for greater efficiency, endurance and/or speed through drag reduction whilst
wading or swimming resulted in the significant hair loss manifest in the difference between humans and the
great apes.
Falsifiable Predictions:
1. Shaving body hair off competitive swimmers should result in gains in swimming performance (efficiency,
endurance and/or speed) through drag reduction which should show a positive correlation between the
amount of body hair shaved off and the amount of drag reduction observed in similar-sized competitive
swimmers.
2. There should be a 'threshold effect' at the point when hair density increases to the point when the boundary
layer surrounding each individual hair merges into one. (Hence explaining why most semi-aquatic animals
- which also tend to move through thick abrasive vegetation - have a thick pelt of hair.)
3. Modern human populations with significant amounts of body hair are not typical of the human universal
status and represent a 'reversion' to greater body hair since the last common ancestor of all human beings
in certain 'Out of Africa' groups, probably due to an early move into temperate climates.
3. The Adipocity for Buoyancy Hypothesis:
The hypothesis that selection for greater buoyancy in water, especially in mother-infant pairs, was at least
partly responsible for the increased adipocity observed in humans as compared to most terrestrial mammals,
all other primates and great apes.
Falsifiable Predictions:
1. Human infants should be significantly more buoyant than those of the great apes.
2. Human mothers would be able to rescue their infants from a 2m deep pool (requiring an element of
swimming) with close to 100% success, whereas chimpanzee mothers would fail to do so almost totally.
This differential would be observed even if the permitted time before rescue attempt tended to zero.
3. The accidental drowning statistics should show a positive correlation between the adipocity of people with
similar age, sex, race, swimming ability, fitness etc and their likelihood to escape near-drowning incidents.
4. Greater adipocity should be especially correlated with successful endurance swimming in colder sea
waters.
4. The Dip-Sweat Cooling Hypothesis: The hypothesis that the sweat-cooling thermoregulatory response to
overheating seen in humans is a water-side adaptation which evolved as an adjunct to the far more efficient
method of cooling of simply going for a dip in near-by bodies of water.
Falsifiable Predictions:
1. Homo sapiens has a greater physiological dependence on fresh water than the great apes and is far more
wasteful of it, not only in sweat cooling but also in more dilute excretory products.
17
2. The universal trait of sweat cooling in not supportable for typical human work-loads in equatorial habitats
unless replenished by copious amounts of fresh water. Earliest Homo sapiens lacked the technology to
transport sufficient water great distances.
3. Going for a dip in a body of water provides a far more efficient (less costly and more rapid) way of
reducing body temperature in hot equatorial climates than sweat cooling.
4. The delay before the onset of sweating as the body re-heats after going for a dip, should correspond closely
with the average time it takes for a wet body to dry.
Acknowledgements
I’d like to thank Kevin Hunt, Elaine Morgan, Marc Verhaegen, Pauline Ross, Stephen Munro, Warren Mitchell,
Charles Oxnard and my wife Lesley for their inspiration, advice and corrections.
A special ‘thankyou’ to the Australiasian Society for Human Biology (ASHB) conference in Canberra, December
2004, for giving me the confidence to put this paper forward for publication, after awarding me the student’s first
prize for my paper presentation: “The so-called ‘Aquatic Ape Hypothesis’: Refuted or just misunderstood?”.
Perhaps this idea is not so crazy, after all.
18
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