Common misconceptions and unproven assumptions about the aquatic ape theory
A Guest Post by Marc Verhaegen
It is often assumed that Alister Hardy’s and Elaine Morgan’s aquatic ape theory (AAT) suggests that more than 5 Ma (million years ago) there was a semi-aquatic phase in our past (explaining e.g. human fur loss, fatness and upright bipedalism), which was followed by a savanna phase on the African plains. In 2011, AAT proponents published an eBook, Was Man more aquatic in the past?, which showed a rather different picture of AAT. Here I very briefly describe my view of ape and human evolution (for details and references, see my publications at the end of this article).
The Homo-Pan last common ancestor (LCA)
My 1994 paper concluded:
… insofar as the fragmentary fossil material and the incomplete comparisons with extant apes allow, ontogenetic and morphological evidence tends to favour the hypothesis that the LCA of Homo and Pan 8–4 Ma was a partially bipedal, gracile australopith with chiefly a mosaic of human and chimpanzee (especially bonobo) features: low sexual dimorphism, minimal prognathism, slightly enlarged canines, non-protruding nasal skeleton, smooth ectocranium without crests, “small” brain with ape-like sulcal pattern, relatively non-flexed basicranium, intermediate position of foramen magnum, “short” forelimbs without knuckle-walking features, low ilia, (very) long femoral necks, “short” legs, (very) valgus knees, full plantigrady, longer and not very abductable halluces …
This conclusion is still correct (except that I would now replace ‘partially bipedal’ by ‘vertical’ or ‘orthograde’). Most paleo-anthropologists now agree that the LCA differed from both humans and chimps today: both lineages acquired evolutionary innovations. Chimps got longer and stronger arms and fingers, much longer iliac blades, a narrower pelvis and shorter femoral necks, more grasping big toes, knuckle-walking etc. Humans got an external nose, a much larger brain, longer and straighter legs etc.
Mio-Pliocene hominoids: aquarboreal?
During the Miocene (23–5.3 Ma) and Pliocene (5.3–2.6 Ma), the early ‘apes’ were quite diverse, but their fossils (e.g. Helio-, Gripho-, Dryo-, Oreopithecus, Lufengpithecus, Sahelanthropus, Orrorin, Ardi-, Australopithecus) were typically found in coastal, flooded or gallery forests, lagoons or wetlands, where they – like lowland gorillas who feed on floating vegetation in the swamp or bai today, but much more frequently – could have eaten aquatic herbs, sedges or papyrus, eggs, crabs, snails and bivalves between reeds or mangroves etc. Such lifestyles – climbing and hanging vertically, grasping branches above the water, wading on two legs, floating vertically collecting floating vegetation etc. – help explain hominoid (ape and human) body enlargement, tail loss, vertical spine, dorsal shoulder blades, and wide thorax and pelvis.
All great apes in the wild are regularly or occasionally seen in the water, but possibly the Pleistocene coolings (Ice Ages 2.6–0.01 Ma) caused the ape ancestors to spend less time in the water, the different ape species to different degrees. Apparently, gibbons kept the vertical body but became smaller arm-swingers in the higher canopy, orangutans elaborated a suspensory lifestyle lower in the canopy, and chimp and gorilla ancestors in parallel reduced their vertical postures to knuckle-walk quadrupedally on the drier forest floor.
In my view, the Homo-Pan LCA ~5 Ma, like all or most fossil hominoids (including the australopiths), was still what Marcel Williams called aquarboreal (aqua=water, arbor=tree). In australopiths, aquarborealism can explain the remarkable combination of curved hand phalanges (branch-hanging), a vertical spine, and flat feet and footprints (wading, swimming): Pliocene australopiths were typically found in swamp and gallery forests, and Pleistocene robust australopiths in more open wetlands, papyrus swamps or lagoons (how the different habilis fossils lived is less clear, some ex-aquarboreal, others ex-littoral?).
Archaic Homo: littoral diving?
If the Homo-Pan LCA lived in African littoral forests along the Indian Ocean or the Red Sea, this could explain the archaic Homo finds ~1.8 Ma as far as Java (Mojokerto, amid barnacles and shells), Georgia (Dmanisi, amid ‘rich lacustrine resources’ near the Black-Capsian Sea connection then), Algeria (Aïn-Hanech floodplain) and the African Rift (erectus appeared at Lake Turkana together with stingrays, suggesting a marine connection then).
Sea-levels repeatedly dropped more than 100 m during Glacials, and on the continental shelves, vast territories – presumably tree-poor and shellfish-rich – became available for intelligent, dextrous, tool-using, coastal forest-dwelling hominoids, who could open mangrove oysters (like capuchin monkeys do) and coconuts (containing fresh water) and beach-comb for turtles and their eggs, mussels and crabs. An extensive overview of the literature by Stephen Munro showed that virtually all known archaic Homo sites (including those in ‘savanna’) were associated with permanent water and edible shellfish, and we can expect that these handy beach-combers on their diapsora to different continents and islands learnt to dip and later dive, gradually deeper, for bivalves, abalone and perhaps seaweeds.
In fact, only regular diving can explain archaic Homo’s pachy-osteo-sclerosis (POS), the extreme thickness and density of cranial and postcranial bones of most erectus-like fossils. In modern humans, such hyper-mineralisation causes brittleness and multiple fractures (osteopetrosis), and POS is only seen in slow littoral divers, e.g. dugong and manatee, walrus, Kolponomos, pakicetids, Odobenocetops, and Thalassocnus spp. Marine biologists agree POS has a hydrostatical function (ballast) – Homo erectus was no exception!
Littoral diving most parsimoniously explains many other features seen in Homo – fossil (e.g. ear exostoses, protruding nasals and mid-face, platycephaly, flattened femora, brain size) and living (e.g. fur loss, SC fat, head–spine–legs in one line, in human newborns vernix caseosa and reniculi). The abundant brain-specific nutrients in aquatic foods (e.g. DHA, iodine) facilitated fast brain growth (sapiens’ poorer post-aquatic diet required a longer youth to grow the same brain size).
From the coasts and estuaries, different Homo populations gradually – at first seasonally, later also permanently – ventured inland along rivers. Neandertals generally have less POS than erectus, their fossils often lay just above those of beavers, and some of their tools bear traces of cattails, so perhaps they hunted or scavenged ungulates amid reeds, but at the coast they still collected shellfish and butchered whales and seals (e.g. Gibraltar).
Homo sapiens: from wading to walking?
Gracile skulls (i.e. loss of POS) of H. sapiens appeared at Omo and Herto in East Africa less than 0.2 Ma, and humans got straighter legs and longer tibias, shorter and more vertical femoral necks, a narrower pelvis, and very long and more vertical spinous processes of the mid-thoracal vertebrae (strengthening the spine in an upright stance?), which suggests our ancestors ~0.2 Ma abandoned regular diving, but often waded vertically on two legs, possibly to better see fishes swimming and spear them from above. They might have slept in reed houses above the water (safer from predators), used reed boats, dugouts, and nets, and spent more and more time outside the water. Maps of human population densities show that, although we have become fully terrestrial today, we are still a waterside species, and almost half of human dietary calories still come from the water (e.g. rice, aquaculture, fish, shell- and crayfish).
The nowadays popular endurance running ideas (e.g. ‘dogged pursuit of swifter animals’, ‘born to run’, ‘le singe coureur’, ‘Savannahstan’) are no doubt among the worst hypotheses ever proposed. In 1987, in Nature, I wrote:
… it is highly unlikely that hominid ancestors ever lived in the savannas. Man is the opposite of a savanna inhabitant. Humans lack sun-reflecting fur, but have thermo-insulative subcutaneous fat layers, which are never seen in savanna mammals. We have a water- and sodium-wasting cooling system of abundant sweat glands, totally unfit for a dry environment. Our maximal urine concentration is much too low for a savanna-dwelling mammal. We need much more water than other primates, and have to drink more often than savanna inhabitants, yet we cannot drink large quantities at a time …
Apparently we evolved running – only lately, and only about half as fast as horses or dogs – in spite of our plantigrade feet, broad build, profuse sweating, and our large fat tissues (~10 % of body weight in lean persons, ~10 times more than in chimps). Of course, there exist a few inland populations in East Africa today where adult men running after ungulates sometimes provide a limited part of the calories, but this dogged pursuit is probably very recent and derived, and it requires a considerable technology (e.g. water bags, weapons, poisons). Quadrupedal chimps can hunt colobus monkeys and even eat them raw, but archaic Homo with their heavy bones (POS), very broad pelvis, shorter legs and flat feet were much too slow on land. In fact, our small mouth, spatulated canines and closed tooth-row, short tongue and smoothly vaulted palate are ill-designed for meat eating, but ideal for consumption of slippery foods.
Unproven assumptions about AAT
My scenario makes clear that, in my opinion, AAT is
– less about becoming aquatically adapted by gradually wading deeper and deeper, than about aquarboreal hominids in densely vegetated swamp or mangrove forests descending into the water below the trees,
not about why Homo and Pan split, but about what happened after the split, not about ‘aquatic apes’ or even australopiths, but about archaic Homo (erectus more than Neandertals), and not about what happened 10 or 5 Ma, but rather about what happened less than 2 Ma, during the Ice Ages, when Homo populations spread along the coasts to England, the Cape and Flores,
less about how modern humans behave in water than about erectus’ differences with us (in my 1996 paper, the data show that erectus differed from sapiens almost as much as it did from A. africanus),
less about bipedalism or even bipedal wading (except <200 ka) than about slow and shallow diving, and not about surface-swimming (as in most Mio-Pliocene hominoids?), but about bottom-diving (where Homo’s food was),
less about what happened in Africa or even the Rift Valley than about what happened on the Indian Ocean or Mediterranean shores, and less about out of or into Africa or Asia scenarios than about coastal diaspora (e.g. on both the African and the Asian side of the Red Sea),
less about a riverine evolution in fresh-water than about a coastal (and perhaps later also riverine) life,
not in the first place about an isolated evolution on Danakil or another island, but about a littoral and estuarine life on African and Eurasian coasts (presumably including islands) during most of the Pleistocene,
not about anthropocentric views, including just-so explanations for ‘unique’ human features (e.g. bipedalism ‘for’ wading, SC fat ‘for’ surface swimming), but about a comparative analysis of our features (e.g. the combination bipedalism + vertical spine is only seen in humans and penguins on land),
not about sudden mutations, saltations or evolutionary jumps from ape- to human-like, but about a gradual mosaic-like evolution in small steps (horizontal arboreal > above-branch aquarboreal > below-branch vertical aquarboreal > littoral > vertical wading > bipedal walking),
and even less about the hominid fossil record than about our embryological, anatomical and physiological ‘scars of evolution’ (Elaine Morgan): ‘the remnants of the past that don’t make sense in present terms – the useless, the odd, the peculiar, the incongruous – are the signs of history’ (Stephen Gould).
In brief, instead of the ‘old’ AAT, I propose:
(1) an aquarboreal theory of Mio-Pliocene hominoids, including australopiths,
(2) a littoral theory of Pleistocene Homo.
Publications on ape and human evolution
- The aquatic ape theory: evidence and a possible scenario. 1985 Med Hypoth 16:17–32
- The aquatic ape theory and some common diseases. 1987 Med Hypoth 24:293–9
- Origin of hominid bipedalism. 1987 Nature 325:305–6
- Aquatic ape theory and speech origins: a hypothesis. 1988 Specul Sci Technol 11:165–171
- African ape ancestry. 1990 Hum Evol 5:295–7
- Aquatic ape theory and fossil hominids. 1991 Med Hypoth 35:108–114
- Aquatic features in fossil hominids? 1991 in Roede ed.:75–112
- Human regulation of body temperature and water balance. 1991 id.:182–192
- Did robust australopithecines partly feed on hard parts of Gramineae? 1992 Hum Evol 7:63–64
- Aquatic versus savanna: comparative and paleo-environmental evidence. 1993 Nutr Health 9:165–191
- Australopithecines: ancestors of the African apes? 1994 Hum Evol 9:121–139
- Aquatic ape theory, the brain cortex, and language origins. 1995 ReVision 18:34–38
- Morphological distance between australopithecine, human and ape skulls. 1996 Hum Evol 11:35–41
- Sweaty humans. 1997 New Scientist 2091:53
- In den Beginne was het Water – Nieuwste Inzichten in de Evolutie van de Mens. 1997 Hadewijch Antwerp
- Oi, big nose!. 2010 New Scientist 2782:69
With Stephen Munro, Pierre-François Puech and/or Mario Vaneechoutte:
- Bipeds, tools and speech. 1999 Mother Tongue 5:161–8
- Hominid lifestyle and diet reconsidered: paleo-environmental and comparative data. 2000 Hum Evol 15:175–186
- The continental shelf hypothesis. 2002 Nutr Health 16:25–27
- Aquarboreal ancestors? 2002 TREE – Trends Ecol Evol 17:212–7
- Possible preadaptations to speech – a preliminary comparative approach. 2004 Hum Evol 19:53–70
- New directions in palaeoanthropology. 2007 in Muñoz ed.:1–4
- The original econiche of the genus Homo: open plain or waterside? 2007 id.:155–186
- Pachyosteosclerosis suggests archaic Homo frequently collected sessile littoral foods. 2011 HOMO – J compar hum Biol 62:237–247
- Early Hominoids: orthograde aquarboreals in flooded forests? 2011 in Vaneechoutte ed.: 67–81
- Pachyosteosclerosis in archaic Homo: heavy skulls for diving, heavy legs for wading? 2011 id.:82–105
- Seafood, diving, song and speech. 2011 id.:181–9
- Reply to John Langdon’s review of the eBook: Was Man more aquatic in the past? 2012 HOMO – J compar hum Biol 63:496–503
M Roede, J Wind, J Patrick & V Reynolds eds 1991 Souvenir London. Aquatic Ape: Fact Or Fiction?
SI Muñoz ed 2007 Nova NY. Ecology Research Progress.
M Vaneechoutte, A Kuliukas & M Verhaegen eds 2011 eBook Bentham Sci Publ. Was Man More Aquatic in the Past? Fifty Years after Alister Hardy.