Trying to debunk the aquatic ape hypothesis… or not. Or the day I tried to defend David Attenborough.

The so-called aquatic ape hypothesis is one that has attracted a lot of attention and much derision. In 1960, British marine biologist Alistair Hardy posited the idea that humans might once have had an aquatic phase (or more accurately a semi-aquatic phases, spending some time in a watery habitat but a significant amount of time on land). This was picked up highlighted in popular zoologist Desmond Morris’s book The Naked Ape . However, Elaine Morgan was one of the the hypothesis’ main promoters, writing a book called The Aquatic Ape Hypothesis . There have been several debunkers of the hypothesis including Southern Fried Sciences’ own David Shiffman although Jim Moore’s website is probably one of the most comprehensive debunking sites for the hypothesis . Today Alice Roberts and Mark Maslin posted a critique of the aquatic ape hypothesis, mostly in response to a new BBC radio series The Waterside Ape which is being presented by David Attenborough.

Proponents of the aquatic ape hypothesis point to a number of adaptations that humans have that are similar to, or might be an advantage for, aquatic species such as: bipedalism, elongated lower limbs, breath-holding and speech, an enlarged pharynx, a nose, paranasal sinuses, the diving reflex, reduction of body hair, highly active of sebaceous glands subcutaneous fat, tears, salt metabolism, webbed digits, tool use, and large brains.

Roberts and Maslin really just pick on just two aspects of the aquatic ape hypothesis for their criticism: hair loss in aquatic mammals and an absence of hominid fossils anywhere but in dry woodland areas. They claim that humans having reduced hair isn’t support for the aquatic ape hypothesis because many marine mammals have hair. As a marine mammal biologist, however, their argument is a majorly flawed one. Marine mammal biology 101 will tell you that in the water hair dramatically loses its insulating properties. Species that have fur do not have this to keep them warm in the water but to keep them warm when they are on land – hauling out during breeding and moulting seasons (often on subpolar or polar islands or ice). Roberts and Maslin illustrate their article with a sea otter – a species that lives in extremely chilly water, has the densest fur of all mammals and has to spend almost 25% of its time grooming its fur to maintain a layer of insulating air in its fur. As soon as it dives underwater, this insulating air is quickly pushed out of its fur, especially as it dives deeper and deeper. In terms of fur coverage, sea otters (and beavers) are rather an oddity in aquatic mammals. However, if early hominids were dwelling in African aquatic ecosystems, they would be encountering a significantly warmer aquatic environment than the chilly waters of the Californian kelp forests or Alaska. Looking at warm, shallow temperature aquatic or semi-aquatic mammals would be a better model of the selection pressures on a hominid in an aquatic environment in Africa – for example manatees, dugongs, the hippopotamus or tapirs.

The second argument that there are no fossil records is something that Desmond Morris commented on more than 4 decades ago. Quite frankly, the global sea level during most of the evolution of early hominids sea levels were substantively lower than they are today, coastal locations which presumably might have been habitats for semi-aquatic hominds are probably several (if not dozens) of meters under water. Absence of fossil evidence is not a logically valid argument if no one is actually looking in areas of potential habitat, i.e. absence of evidence is not necessarily evidence of absence.

The aquatic ape hypothesis gets a lot of criticism, probably because many of the proponents  leap at dubious or pseudo-science to make their claims. Elaine Morgan’s book certainly cherry picked data and had a tendency to use studies that had been disproven, which undermined the argument. Recently, the infamous fake documentaries on mermaids shown by the Animal Planet TV channel have used the aquatic ape hypothesis as a ‘scientific’ justification for their shows, which certainly doesn’t help the idea’s reputation. But most modern scientist proponents of the hypothesis don’t propose that humans went through some sort of fully aquatic mermaid stage during their development (at least no serious scientists) but rather a hominid that had a river/lakeside, wetland or coastal habitat (in fact this is what Hardy originally suggested). I assume that is why the Attenborough show is called The Waterside Ape, rather than The Aquatic Ape.

Is the idea, that early hominids might have lived next to coats or waterways and forages on shallow water aquatic species so outrageous?

There is some evidence early humans may have had a notable of their diet being aquatic sourced (postulated both biochemically and from fossil evidence . There is even diving physiology research that places humans with many aquatic and semi-aquatic species  in terms of their diving capability. Is the idea that some hominids were coastal and maybe waded into lakes or rivers and duck dove to collect shellfish so weird? There are plenty of historical and recent human cultures where free diving for shellfish provided much of their diet. There are apes now that forage on beaches such as Japanese macaques or capuchin monkeys. Both species are known for their intelligence and tool use, including using stones to smash open shellfish. Many primate species live in coastal mangroves or wetlands. Would a waterside habitat really be so odd? Might humans’ proficiency in tool use be linked to hominids shucking shellfish with a rock while sitting on a beach in on the coast of Africa.

Unlike Roberts and Maslin, I am not so quick to poo-poo David Attenborough’s new radio show as pseudo-scientific bunkum. I’d certainly like to hear what scientific evidence is brought up first, rather than dismissing the idea out of hand.

A link to The Waterside Ape radio show can be found here: http://www.bbc.co.uk/programmes/b07v0hhm