The aquatic ape hypothesis (AAH) proposes that our evolutionary ancestors, at some point, adapted to a semi-aquatic existence. This challenges the consensus view that our ancestors left an arboreal (tree-dwelling) habitat and then continued to evolve in the terrestrial habitat of the African savannah. One of the most passionate proponents of the AAH is the writer Elaine Morgan. She details the hypothesis in her book The Aquatic Ape Hypothesis (1999) as well as in this more recent TED talk. Morgan was frustrated at how a male-centred picture of human evolution was being popularised. According to this view, the reason why our ancestors lost their hair was that male hunters needed to sweat while chasing game. However, this does not explain why women also lost their hair, since they weren’t chasing game. Morgan set out to explain our loss of overall body hair – as well as other peculiar features of humans – with a more controversial hypothesis.
The hypothesis can be traced back to Professor Alister Hardy, who wrote an article in 1960 for New Scientist entitled Was Man More Aquatic in the Past? It is well known in evolutionary theory that sea life evolved into land life, with some animals going back into the water (i.e. the ancestors of modern marine mammals: seals, dolphins, whales and walruses). Hardy asserts that the obvious physical differences between humans and our ape relatives demand a new explanation. Hardy’s thesis is that our arboreal ancestors were out-competed and were forced to leave behind their life in the trees. They went to the shores to feed on shell-fish and sea urchins. This stage in evolution took place in the more tropical seas, where our hominid ancestors could spend long periods of time in the warm waters. Hardy imagines our ape-like ancestors wading at first but then eventually becoming more skilled at swimming. Swimming then led to diving so that our ancestors could better hunt for shell-fish, worms, crabs, sea-urchins, bivalves and – with increasing catching abilities – fish.
It’s an interesting narrative. But is there any evidence to support it? Hardy believes there is plenty. The first thing to consider is our exceptional ability to swim, and for long periods of time. No other terrestrial animal can rival this ability so easily and gracefully swim on the surface and dive below it. For Hardy, this is a clear indication of an earlier adaptation to a semi-aquatic life. We should, however, keep in mind that other terrestrial mammals are able to wade and swim, including dogs. This example of diving, featured on the BBC series Human Planet, is a pretty staggering example of our adaptation to water. It is true that human infants have to be taught how to swim, but then again, so do young otters.
Hardy also poses the following question: “Does the idea [AAH] perhaps explain the satisfaction that so many people feel in going to the seaside, in bathing, and in indulging in various forms of aquatic sports?” Indeed, these seem to be universal human pass times. Not only do we enjoy relaxing by the seaside, but we find the whole scene very beautiful. This aesthetic appreciation of the seashore could be a vestige of our aquatic ape ancestors. Our aquatic apes would have evolved to value the seashore as a source of food so the sight of it would set off the reward systems in our brain. Our attraction to the seashore is, therefore, a by-product of our ancestor’s dependency on it for survival. Our desire to sit by the beach, listen to the waves rolling back and forth, or to go swimming in the sea could be a desire which has a very ancient origin.
A similar explanation is given for our aesthetic appreciation of landscapes. Finding beauty in landscapes and expressing this beauty through art (drawing, painting, photography) is pretty much universal among the human species. From an evolutionary point of view, landscapes were highly valuable for our nomadic ancestors who were constantly on the move. The experience of seeing a landscape (rivers, lakes, forests, grasslands, vegetation, mountains, etc.) was an opportunity for our ancestors to explore new territories. Such opportunities were highly sought after since the view of a landscape includes the promise of water, food and shelter. Furthermore, features of landscapes would serve as landmarks for our ancestors to help them remember where shelter might be, for example.
Dennis Dutton, in his essay Aesthetics and Evolutionary Psychology, expands on this idea. He refers to an experiment (Orians and Heerwagen, 1992) which found that children, when showed a range of landscape photography, preferred the savannah landscape with trees – the same environment where early human evolution took place. There was also a general preference for landscapes with water, open and wooded spaces (allowing for hunting and hiding), trees that fork near the ground (opportunities to escape in case of predators) and vistas the recede in the distance, including a path or river that bends out of view, which invites exploration. The direct presence of game animals was also valued. This is exactly the same food-rich environment that our hunter-gatherer ancestors would have thrived in. In 1993, two Russian artists, Vitaly Komar and Alexander Melamid, carried out a project to find out the art preferences of people in 10 different countries. Cultural uniformity was discovered – all of the people preferred the classic landscape scene.
So, our aesthetic appreciation and enjoyment of the seashore could have an evolutionary basis after all. But Hardy points to other pieces of evidence as well to support the AAH. One of the most compelling pieces of evidence, Hardy argues, and which Elaine Morgan re-iterates, is our loss of hair. The loss of hair is characteristic of many aquatic mammals: whales, manatees, dugongs and hippos. We retained all of the hair on our head because the head was the only exposed part for aquatic apes. The hair on our head would have protected our ancestors from the rays of the tropical sun. Losing our hair also made us adapted to the water because it reduced resistance while swimming.
Hardy also refers to the graceful shape of humans, the sweeping curves of our body, and how this makes us streamlined for swimming. Our ape cousins have none of these features. One criticism of this argument is that many marine animals have fur and are excellent swimmers: fur seals, otters, beavers and polar bears, for example. In addition, humans aren’t really that streamlined compared to aquatic mammals. A truly streamlined aquatic animal is shaped more like a torpedo. Humans, on the other hand, have curves and protruding joints which act as resistance in the water.
Another way in which humans differ from apes also relates to our skin. Humans, unlike apes, have subcutaneous fat or fat below the skin. Aquatic mammals (whales and seals, for example) also share this layer of fat below the skin, which we would call ‘blubber’. In warm-blooded aquatic animals, these layers of fat serve to prevent heat loss and so in terms of their function, they replace the hair. Brian Dunning, who hosts the Skeptoid podcast had the following to say about this:
…the claims made by aquatic apers about body fat is factually wrong. Humans do have subcutaneous fat, but it’s just like what the other great apes have, and is very unlike the blubbery fat developed by the furless aquatic mammals. An aquatic ape’s subcutaneous fat would not be like a whale’s insulating, buoyant blubber.
While this may be true, what Dunning fails to stress is that humans have the thickest layer of subcutaneous fat out of all the primates. Bear in mind though that this does not necessarily support the AAH. Marine animals have much thicker layers of fat surrounding the whole body, whereas, for humans, it only surrounds certain parts and in relatively thin layers.
Other human features have been used to support the AAH, including bipedalism (walking on two feet), our descended larynx and the shape of our nose. However, these features can be explained in a way which is consistent with the standard non-aquatic picture of evolution. Despite the view that bipedalism made our ancestors better adapted for wading and swimming, bipedalism is clearly advantageous on land as well – after all, it allows for long-distance running. While the evolution of bipedalism is still hotly debated, the explanations which assume the non-aquatic view include: freeing our hands for tool use, carrying infants, feeding adaptations and improved use of energy. Despite the claim that the descended larynx made diving easier, the generally accepted view is that it descended to facilitate speech. Likewise, our hooded nose did not evolve to prevent us from breathing in water but to facilitate speech. Speech requires an impressive degree of breath control. And with respect to our hairlessness, an alternative explanation for our loss of hair is that it helped our ancestors avoid parasites, while also allowing us to dissipate heat quicker and cool us down.
Morgan in The Aquatic Ape Hypothesis points out that babies instinctively hold their breath when submerged under water. This is known as the ‘diving reflex’. However, this reflex – this ‘aquatic feature’ – is not unique among primates; it is found in other mammals as well. Newly born infants will sort of swim around when placed in water as well, but it is not really true swimming. It is unclear whether this points to a more ancient aquatic life.
The AAH is currently considered a fringe theory, with little acceptance from mainstream scientists, probably because none of Morgan’s work has appeared in any peer-reviewed journals. In addition, it is not clear whether the fossil record of our hominid ancestors serves to bolster the hypothesis. Paleontologist Darren Naish highlights that “fossil evidence that might support the AAH has not appeared”. Furthermore, the similarities between humans and aquatic mammals can be explained in ways relating to the standard picture of human evolution. According to the critics, adding in a time period of semi-aquatic existence in our evolution only complicates matters. And if we follow the principle known as Occam’s Razor, it is best to prefer the simplest explanation or the explanation with the fewest assumptions.
Admittedly, the AAH lacks the body of evidence necessary to validate it as a scientific theory, or even as a strong scientific hypothesis. Here we find a very comprehensive scientific critique of the AAH laid out by primatologist Jim Moore. The current consensus view of human evolution, which says that hominids lived an exclusively terrestrial life, seems to have more explanatory power than the AAH and it is consistent with the fossil record as well. But this does not mean that we should necessarily discard the AAH. After all, it is possible that it could one day be vindicated. The reason why we find the sea-shore pleasant and beautiful is still a mystery that perhaps only the AAH can explain. Or there may be another explanation still to come.