The Waterside Hypothesis: wading led to upright walking in early humans

06/02/2023

Our ancestors lived in aquatic habitats according to the controversial but highly plausible Waterside hypothesis, formerly known as the Aquatic Ape Theory. Frequent wading in water led, among other things, to our most striking feature: walking upright on two legs. However, many paleoanthropologists believe that bipedalism is the result of a supposed move from jungle to savannah, an idea that sprang from the now largely obsolete savannah hypothesis. The opposing views in human evolution are amongst the fiercest and ugliest of debates in the scientific arena. But while the aquatic past is far from being widely accepted, it has the support of the likes of Sir David Attenborough and Dr Desmond Morris.  

Author: Kathelijne Bonne; arguments provided by Marc Verhaegen.

This article is the first part of a series on our ancestors and their extended family, their way of life, kinships, landscapes in which they lived, and migrations (not only in Africa but also in Eurasia). Belgian physician Dr. Marc Verhaegen, author of the book Human Evolution: why we walk upright and can speak (2022, currently only in Dutch), helped me with many arguments. His findings from anatomy and comparative biology have greatly refined current knowledge, as well the work of a dedicated international community of researchers that supports and refines, against the tide of dogma, the Waterside Hypothesis.

By challenging dogma-infused theories such as the Savannah Hypothesis, we hope to open the debate and better understand, with an open mind and without self-righteous afro- and anthropocentrism, how we are today. The evolution of humans and primates is indeed quite fascinating.

The Waterside Hypothesis has been under attack for decades. It's been derided, taken out of context, ignored by 'serious paleoanthropologists' and labeled pseudoscience and worse. But the scientific arguments, from anatomy and comparative biology of both living and fossil humans as well as great apes, are overwhelming and certainly cannot be ignored. Yet is it very inconvenient to the current establishment and the paradigm shift would be so great that it would impact the careers of many. The opponents support the old savannah hypothesis and related theories that are entrenched in Victorian dogmas.

Wading, looking for food. (K.Bonne)
Wading, looking for food. (K.Bonne)

Ideal savannah image?

During the Miocene, the epoch that lasted from 23.03 to 5.33 million years ago, the climate was more tropical than today and dense rainforests were widespread. Toward the end of the Miocene (starting about 8 million years ago) it gradually became drier and rainforests gave way to more open landscapes, such as savannas (although rainforest were still abundant). The "classical" savannah hypothesis holds that our ancestors descended from the trees and moved to the savannah to run around upright, on two legs, and become hunters. This transition would explain man's unique anatomy: bipedalism, upright, no fur, large brain, ...

Kinships and splits between great apes throughout geological time (image: K.Bonne)
Kinships and splits between great apes throughout geological time (image: K.Bonne)

But these assumptions don't actually hold water. Walking upright on two legs is not at all a good adaptation to a dangerous open habitat such as the savanna. Moreover, early great apes walked upright long before savannas became widespread, as is becoming increasingly clear from biological evidence. Yet many paleoanthropologists continue to adhere to the savannah hypothesis because it fits the entrenched anthropocentric, even macho-like picture of 'fast clever man chasing wild animals on the savannah', distancing himself in any sense from the 'lame dumb ape sitting in a tree chewing on a piece of fruit'. This "ideal" image took shape in the days when Victorian gentlemen regarded 'man' as the pinnacle of evolution.

Human evolution according to Darwin

Charles Darwin correctly noted that the gorilla (genus Gorilla) and the chimpanzee (genus Pan) are the closest living relatives of humans (genus Homo), long before genetics proved it and when creationism still thrived. Gorillas and chimpanzees today live in the jungles in Africa and are rather four-footed (knuckle walk). Therefore, Darwin thought that our ancestors also lived in African jungles, walked on their knuckles, and only started walking upright when they left the forest to conquer the savannah.

Darwin was quite right about the close kinships and many other things, but not about the savannah (and perhaps not about Africa either). On the contrary, primates that migrate from the trees to the plains become even more quadrupedal, as is the case with the savannah baboon. This is the only primate on the savannah, and yet it sometimes wades - upright - in search of aquatic plants.

Imagine a bare, upright walking ape or human, without weapons, claws, hooves, big canines or a set of horns. Wouldn't he or she be very vulnerable and defenseless in such a dangerous unsheltered habitat full of savage and fast running animals and under a scorching African sun?

Waterside Hypothesis

Relying on various inconsistencies and built-in biases about the superiority of humans in the savanna hypothesis, marine biologist Sir Alister Hardy and writer Elaine Morgan developed the Aquatic Ape Theory (AAT) in the 1960-70s. It provided a very plausible explanation for, among other things, traits such as bipedalism and the loss of fur. The savannah adherents were infuriated see the good old ideas that sustained the human evolution under threat, and spared no effort to sink the aquatic ape hypothesis. 

Model for evolution of great apes from Wikipedia, vertical scale 0-10 Ma (million years) - a typical anthropocentric-biased model: note how few side branches (relatives) Pan and Gorilla have, while the human branch (blue), looks like an overloaded Christmas tree.
Model for evolution of great apes from Wikipedia, vertical scale 0-10 Ma (million years) - a typical anthropocentric-biased model: note how few side branches (relatives) Pan and Gorilla have, while the human branch (blue), looks like an overloaded Christmas tree.

Even a great scholar of our time, Richard Dawkins, fails to rise above the dispute, saying the Waterside Hypothesis is fanciful in his otherwise very good book "The Story of Our Ancestor" while the savannah theory itself rests on dogma. An authority like Dawkins may want to choose to stay neutral. Unsuspecting readers should be able to form an own opinion, as human evolution is far from being resolved.

Aquatic ape?

Elaine Morgan and Alister Hardy situated our most intense aquatic phase very early: more than 5 or even 10 million years ago, long before humans came into existence. That's why they used the English word ape. But we are now half a century later and there are new insights. The most intense phase would have occurred later, probably in the early to middle Pleistocene (1.8 to 0.126 Ma), according to Marc Verhaegen. Therefore, Waterside Hypothesis is a more appropriate name.

Aquarboreal: wading-climbing in aquatic forests

Evolution proceeds gradually in small mosaic-like steps in different directions. But a common thread can be drawn. As Marc describes in his book, it is quite possible that evolution proceeded like this:

Early hominoids (early great apes including the ancestors of humans) evolved from four-footed primates that lived in trees until about 25 million years ago. In the early Miocene, they began to explore lower levels and their way of life became increasingly water-bound: while wading-climbing, they moved around tropical water and swamp forests. This way of moving, hanging and clinging to branches and often half-submerged to wade, has been called aquarboreal (from the Latin aqua and arbor), term coined by Marcel Williams. It promoted an upright posture and bipedal locomotion, and they increasingly did so.

Then, passing the Pliocene and arriving in the Pleistocene, the genus Homo had emerged from aquarboreal hominoids. These early humans didn't climb anymore but walked upright (for they were already "pre-adapted" to that) lived in littoral forests along coastlines (Homo litoralis?). They dived in the sea in search of shellfish, among other things. They dispersed and migrated along coastal forests and rivers. Still much later, Homo sapiens eventually walked upright. With long legs, he/she still often waded in shallow water but also walked around on terra firma.

So the early to mid-Pleistocene was the time when our ancestors were most strongly water-bound. The term "water ape" is hence somewhat misleading because it refers to humans and not just great apes. That is why Waterside hypothesis sounds better today.

Great apes like the orangutan sometimes still walk upright (photo Yyangkok/Wikipedia).
Great apes like the orangutan sometimes still walk upright (photo Yyangkok/Wikipedia).

(Bio)logical arguments

Here we cover a few hypotheses, based on (bio)logical arguments, related to our aquatic ancestry:

  • Human ancestors had an aquarboreal lifestyle and dispersed along coasts, watersides and rivers, and not through the savannah,
  • Bipedalism is not just a characteristic of human ancestors (that is an anthropocentric view), but existed much earlier, albeit in a somewhat different form (wading upright and hanging and clinging to branches),
  • Most or even all of the discovered Australopithecus (a genus of great apes/hominoids), such as the famous Lucy fossil, were not ancestors of humans, but were rather related to gorillas or chimps, and
  • We must not have evolved in Africa, but rather in South Asia (but we will discuss that elsewhere).

Below, Marc Verhaegen discusses these hypotheses:

No savannah animal

Early humans in the Plio-Pleistocene did not roam the savannah but dispersed along coasts and rivers. Nor were they hunters of antelope and the like, much less long-distance runners (endurance running). This is because fast animals do not have flat feet, but run on their toes (predators) or even on their nails (ungulates), they do not sweat salty water in dry regions far from the sea, they do not possess a layer of fat, but do possess fur that reflects sun rays, they are narrowly built, and run twice as fast as we do.

We humans clearly experienced a (partial) aquatic phase, which has left traces in our bodies. Perhaps we once ate mostly shellfish, very rich in brain-specific nutrients, such as the polyunsaturated fatty acid DHA. Our subcutaneous fat layer, loss of fur, external nose and perhaps the groove in our upper lip (philtrum), random breath control, stretched physique, flat feet with short toes, spectacular brain enlargement, dexterity and tool use, etc., can all be attributed to an aquatic environment.

Today we still carry numerous ex-aquatic features, but our Pleistocene relatives were most water-bound: they were first discovered on Java in Southeast Asia (Homo erectus), reached islands far overseas such as Flores (Homo floresiensis), they spread in the Pleistocene along the coasts as far as Europe (Homo neanderthalensis) and Africa.

As far as we know today, early Pleistocene Homo erectus was the most strongly water-adapted: they exhibited pachy-osteo-sclerosis (literally "thick-bone-dense"), a very heavy skeleton, occurring only in slow and shallow diving animals in salt water, to facilitate diving, as in the first pinnipeds (including seals) and first cetaceans, and in manatees still today.

Bipedalism: not exclusively human

Paleoanthropologists still believe that the distinction between humans and apes is our two-leggedness.Because many fossils show bipedalism, fossil hunters in Africa always discover - very peculiar! - "hominins," by which they mean "ancestors of man" or at least closer relatives of ours than of the African great apes. They never find fossil ancestors of African great apes (would they yield fewer grants than fossils of human ancestors?). Therefore, they declare Australopithecus (further abbreviated as apiths) exhibiting bipedalism, "thus" as human ancestors.

But the Plio-Pleistocene apiths, e.g., the well-known fossils Lucy, Mrs. Ples or the Taung Child, according to Marc Verhaegen, were not fossil ancestors of humans at all as paleoanthropologists think afro- and anthropocentrically. They were more closely related to Gorilla or Pan. Mio-Pliocene great apes were simply bipedal very early on, and bipedalism is not exclusively human.

From palm walk to knuckle walk?

The extant great apes descend from vertical waders-climbers, but became quadrupeds again (this may have happened fairly late, perhaps not until the Pleistocene). An important indicator of an earlier bipedal phase is their way of locomotion: they place the knuckles of the hands on the ground when they walk on all fours, unlike other apes and monkeys (and human babies!) who walk on their palms. But Pan and Gorilla had become knuckle-walkers, leaning on the back of the middle phalanges, and Pongo, the Asian orangutan, became a fist-walker. Also important, Gorilla and Pan place their knuckles differently; transverse vs. parallel, they thus evolved in parallel, separately from each other.

The transition from palm to knuckle or fist walk can only have been possible through an intermediate stage when the hands were used little or not at all for support, namely, they walked upright for a time. They probably didn't walk like Homo erectus, but more likely had an aquarboreal (wading and climbing) lifestyle. Even today great apes still do all kinds of things in an upright posture. Lowland gorillas, bonobos and orangutans for example walk on two legs into jungle swamps in search of sedge, water lilies, rice, eggs, etc. (google e.g., bonobo wading).

Even the lesser apes (gibbons and siamang) are still "erect" (orthograde) in terms of physique, although no longer for wading: they often walk two-legged on branches, but even more so they sway their arms from branch to branch, with a vertical spine column.

In short, two-leggedness does not distinguish humans and certainly apiths from other great apes.

Lucy not a human ancestor

Thus, if Miocene great apes were aquarboreal, vertically wading-climbing in aquatic forests, there is no reason why the famous two-legged apiths like Lucy should not be fossil relatives of Pan or of Gorilla. Moreover, the earliest discoverers of apiths had no doubts: their fossils were of great apes, they said. In 1924, Raymond Dart called his Taung-child fossil Australopithecus africanus, "African southern ape". Only later did they reason that it walked on two legs, and 'therefore' must have been an ancestor (or close relative) of humans. But detailed comparisons by separate, mutually independent researchers leave no doubt: apiths are more closely related to Pan or Gorilla than to Homo. Both detailed anatomical comparisons and craniodental measurements place the East African Australopithecus afarensis and A. boisei with Gorilla, and the South African A. africanus and A. robustus with Pan.

Wading further ...

So much for our first plunge into understanding our fascinating past. Thanks to growing evidence, and new and revisited paleoanthropological finds, the Waterside Hypothesis cannot fail to resurface after decades of opposition. Open-minded people like David Attenborough support the Waterside Hypothesis and talked about it this BBC4 podcast "The Waterside Ape", where he gives the floor to Marc Verhaegen and noted anthropologist Desmond Morris, among others.

In a subsequent article, we will wade further and develop new hypotheses, including how plate tectonics influenced or perhaps caused hominoid evolution. So hold on (to the branches of the trees) to learn other amazing things about human evolution.

Note: Although in this article the Waterside Hypotheses is explained by Marc, there are many other important and prominent authors, researchers and advocates, such as Algis Kuliukas, Mario Vaneechoutte, Stephen Munro, Franceska Mansfield, John Foss, José Joordens, Peter H. Rhys Evans, ... , and many others.

Sources 

Verhaegen, 2022, De evolutie van de mens: waarom wij rechtop lopen en kunnen spreken, Eburon, 326 p.

Verhaegen, 2013, The Aquatic Ape Evolves: Common Misconceptions and Unproven Assumptions About the So-Called Aquatic Ape Hypothesis. Human Evolution, Vol 28, p. 237-266.

Verhaegen, Puech and Munro, 2002, Aquarboreal ancestors? Trends in Ecology and Evolution, Vol 17(5), p. 212-217.

Verhaegen, 1990 Human Evolution 5:295-7 African ape ancestry.

Verhaegen, 1994 Human Evolution 9:121-139 Australopithecines: ancestors of the African apes?

Verhaegen, 1996 Human Evolution 11:35-41 Morphological distance between australopithecine, human and ape skulls.

Article written by Kathelijne Bonne, geologist and soil scientist. I also write on Good Climate News

The arguments of this article have been provided by Dr. Marc Verhaegen, physician and specialist in comparative biology and paleoanthropology, active in the field of paleoanthropology for over four decades.

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