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Writing a book about the history of one small part of science (in my case, the measurement of gravity) almost inevitably gives one an interest in scientific controversies in general, and a series of minor events led me to an article by Professors Alice Roberts and Mark Maslin entitled Sorry David Attenborough, we didn’t evolve from ‘aquatic apes’ – here’s why. It was first published in Scientific American more than six years ago, so it is hardly of current interest, but is a good example of how a scientific debate can sometimes be carried on in a most unscientific fashion, even by the most reputable of scientists. What had aroused the ire of these two professors was the credence given by David Attenborough in a BBC podcast to the idea that the evolution of Homo Sapiens might have included a period, or periods, during which what was basically a chimpanzee began to adopt a semi-aquatic life style.

As a starting point for this idea, it is worth noting that, externally at least and despite having almost 99% DNA correspondence with the Pan troglodytes and Pan paniscus, the ‘third chimpanzee’, as homo sapiens has sometimes been dubbed, is strikingly different from them. This is something that requires explanation, and the ‘aquatic ape theory’ is one attempt to provide it. The professors, however, are having none of it. They say that “Occasionally in science there are theories that refuse to die despite the overwhelming evidence against them. The aquatic ape hypothesis is one of these, now championed by Sir David Attenborough in his recent BBC Radio 4 series The Waterside Ape.”

Well, that is clear enough. All that is needed to complete the case is the evidence. Not in detail, of course; that would be too much to expect from a relatively short article, but at least sufficiently well stated for the conclusion to be conclusively overwhelming.

Brighton beach during the heatwave in the summer of 2022. Is this a snapshot of a semi-aquatic animal at play?.

First, however, and reasonably enough, the duo give a summary of what the argument is all about.

“The hypothesis suggests that everything from walking upright to our lack of hair, from holding our breath to eating shellfish could be because an aquatic phase in our ancestry. Since the theory was first suggested more than 55 years ago, huge advances have been made in the study of human evolution and our story is much more interesting and complicated than suggested by the catch-all aquatic ape hypothesis..

In 1960, marine biologist Alister Hardy published an article in New Scientist, titled: Was man more aquatic in the past? He re-told the familiar tale of the evolution of land animals from ancient fish, and then considered the return of various groups of reptiles, birds and mammals to an aquatic existence: ichthyosaurs and plesiosaurs, crocodiles, sea-snakes, penguins, whales, dolphins and porpoises, manatees and dugongs, and seals – as well as polar bears, otters and water voles, who hunt in water. Then he suggested that many of the unique characteristics of humans and their ancestors, marking them out as different from the other apes, could be explained as adaptations to spending time in water.

Hardy put forward all sorts of features which could be explained as “aquatic adaptations”: our swimming ability – and our enjoyment of it; loss of body hair, as well as an arrangement of body hair that he supposed may have reduced resistance in the water; curvy bodies; and the layer of fat under our skin. He even suggested that our ability to walk upright may have developed through wading, with the water helping to support body weight.

For Hardy, this aquatic phase would have occupied the gap in the fossil record that then existed – between around 4m and 7m years ago. He sensibly concluded his paper saying that this was all only speculation – a “hypothesis to be discussed and tested against further lines of evidence”

In the 50-odd years since the presentation of this hypothesis, it has enjoyed a certain fame – or perhaps notoriety. The writer Elaine Morgan championed it in her book The Aquatic Ape, and developed the hypothesis further, marshalling a seemingly impressive range of characteristics to support it, including breath control and diet. It seems such a tantalising and romantic idea – but a closer look at the evidence reveals it to be little more than that.”

Having summarised the idea, Roberts and Maslin then set about “pouring cold water on it”. They wrote:

“All the suggested anatomical and physiological adaptations can be explained by other hypotheses, which fit much better with what we actually know about the ecology of ancient hominins. Hairlessness, for instance, is only a feature of fully aquatic mammals such as whales and dolphins. Semi-aquatic mammals such as otters and water voles are extremely furry. Sexual selection and adaptations to heat loss better explain our pattern of body hair. Sexual selection may also explain our body fat distribution, which differs between the sexes.. Voluntary breath control is more likely to be related to speech than to diving.“

It has to be said that to the non-specialist reader, the reader, for instance, of the Scientific American, this might seem more underwhelming than overwhelming. The link (in the on-line version of the original article) is to Robert’s own book and we can anticipate the quality of the evidence presented there by the quality of the evidence in the article. Otters and water voles are much smaller than humans, and the semi-aquatic hippopotamus, which is obviously much larger, has very little hair, so the best that can be said about that argument is that the jury is still out and unlikely to return soon. To offer sexual selection, the well-known evolutionary catch-all when all else fails, as an explanation, coupled with the words ‘may explain’ is hardly convincing, and neither is the ‘more likely’ in the final sentence in relation to voluntary breath control. One has to say that these banner-carriers for rigorous science are hardly living up to the standards they set for others.

The vague and unscientific lack of quantification continues in the paragraphs that follow.

“The diet of many of our ancestors certainly included marine resources – where people lived on the shores of lakes or the sea. But this was a relatively late development in human evolution, and humans can also survive and thrive on food obtained entirely on land. Compared with other animals, we are not actually that good at swimming, and our skin leaks as well, letting in water so that our fingers become prune-like after a long bath.”

What, one has to ask, does ‘relatively late’ mean? We have no idea, and our professors give us no clues. ‘Compared with other animals’ is a scientifically disgraceful statement. What other animals? We are certainly far better at swimming than the other great apes, or most monkeys. As for our wrinkled skin, if our skin leaks so badly, why is it that only our fingers and feet wrinkle? Recent research suggests an answer that would, in fact, favour the ‘aquatic ape’ hypothesis.

However, there was more ‘evidence’ to present.

“What about walking on two legs? That’s something all apes do a bit of – while wading in water, certainly, but also while reaching for fruit, performing aggressive displays or simply moving around in trees. If we evolved from ancestors who already stood up in trees, we don’t need an extraordinary explanation for why we ended up standing on the ground rather than running around on all fours.”

An argument that immediately prompts one to ask why it is that the baboon, the only other member of the ape-monkey lineage that has indisputably adapted to the savanna environment, has failed to find any advantage in two-legged locomotion, the source, in humans, of so many medical problems? There is, however, more, for those who have yet to be overwhelmed.

“Since Hardy and Morgan’s hypothesis was advanced, many of the gaps in the human fossil record have been filled, with at least 13 new species found since 1987. We have also made great strides in reconstructing the environment in which our ancestors lived. And we know that species as far as part in time as Sahelanthropus tchadensis 7m years ago and Homo erectus 2m years ago all lived in forested or open woodland environments. While some of these woods included wetland, this was just part of the mosaic of habitats that our ancestors learned to survive in, and there is absolutely no trace of a hominin ancestor as aquatic as that described by Hardy and Morgan.

We also have evidence our ancestors had to survive periods of extremely dry climate with little or no aquatic resources. Coping with these highly variable, patchwork environments required behavioural flexibility and co-operation, and our large brains and ultra-social nature likely emerged as a result. This flexibility ultimately led to the invention of culture and technology.”

Remarkably, in this section these two very reputable scientists have to resort to the word ‘likely’ to make their case, and they seem blind to the possibility that ‘extremely dry climates’ in the African rift valleys, which are not thought to have ever caused to deep rift lakes to dry completely but would certainly have diminished the resources of the  surrounding terrain, might have made early hominids  more dependent on water, where it was to be found, rather than less. In her TV series entitled The Incredible Human Journey, Professor Roberts revealed herself as a fan of the Endurance Running Hypothesis, which supposes that early man, although not able to outrun his dinner in the short term, could eventually catch up with it because his or her better bodily temperature control would reduce the risk of overheating. But human temperature regulation requires access to plentiful water supplies. Having spent some years working in central Australia, I found her on-screen demonstration of this form of hunting totally implausible. This woman, I thought, had better not be far from water, or she will die.

That, really, is the end of the scientific arguments presented. The final paragraphs simply present opinions as if they were facts.

“Recent proponents of the aquatic ape hypothesis have pointed to much later watery adaptations, including early archaeological sites where humans have been shown to be exploiting coastal resources. But these don’t have much to say about the origins of bipedalism, more than 6m years before – they just demonstrate the behavioural flexibility of later hominins.

Too extravagant and too simple

“The original idea, and certainly Elaine Morgan’s elaboration of it, became an umbrella hypothesis or a “Theory of Everything”; both far too extravagant and too simple an explanation. It attempts to provide a single rationale for a huge range of adaptations – which we know arose at different times in the course of human evolution. Traits such as habitual bipedalism, big brains and language didn’t all appear at once – instead, their emergence is spread over millions of years. It’s nonsense to lump them all together as if they require a single explanation.

Despite the evidence stacked up against the theory, it is strangely tenacious. It has become very elastic, and its proponents will seize hold of any mentions of water, fish or shellfish in human evolution, and any archaeological sites found near coasts, rivers and lakes as supporting evidence. But we must always build our hypotheses on, and test them against, the hard evidence: the fossils, comparative anatomy and physiology, and genetics. In that test, the aquatic ape has failed – again and again.

It is a great shame the BBC recently indulged this implausible theory as it distracts from the emerging story of human evolution that is both more complex and more interesting. Because at the end of the day science is about evidence, not wishful thinking.”

Reading this reminded me forcefully of the scientific battles over sea-floor spreading and plate tectonics that were taking place during my early days as a geophysicist. In the end, a compromise has been reached. Plate tectonics explains much about the way the Earth works, but not everything. Perhaps a compromise might be reached in this area also. The two professors clearly hope that this will not happen,and the aquatic ape will quietly disappear. That may be real wishful thinking.