In 1960, Sir Alister Hardy, a marine biologist knighted for his contribution to the fisheries industry, gave a talk at the British Sub-Aqua Club (a scuba-diving club) and a month later published an article in New Scientist on that talk, called “Was Man More Aquatic in the Past?” Although the idea caught people’s fancies and garnered some attention by the newspapers, it showed little sign of the long-lasting popular appeal it would eventually have.
It didn’t happen overnight. Even with the original article and a follow-up transcript from a radio program, it was 7 years before Hardy’s idea got much notice—this time with a two-page write-up by Desmond Morris in The Naked Ape.
Elaine Morgan, at the time an Oxford graduate in English and a TV scriptwriter, entered the scene in 1972 with the book Descent of Women, the idea for which she got from Desmond Morris’s book. This book proved to be very popular, and in time Morgan followed it up with many articles as well as four more books on the subject (in 1982,1990,1994, and 1997).
During the 1980s, other proponents arrived on the scene, chief among them a medical doctor from Belgium, Marc Verhaegen. A 1987 conference on the subject resulted in a book presenting opposing views, The Aquatic Ape: Fact or Fiction?
The coming of age of the Internet in the 1990s brought the advent of the online venue for presentation and debate, and this subject proved popular. As with many subjects connected with humans and especially human evolution, much of the debate is rancorous and ill-informed. There are nuggets of gold in the online debate; however, just as with the mineral, finding these nuggets requires a lot of panning.
The Aquatic Ape Theory or Aquatic Ape Hypothesis (aka AAT or AAH—this entry will refer to it as the AAT/H) hypothesizes that humans went through an aquatic or semiaquatic stage in our evolution, generally said to have occurred during the transition from the last common ancestor we shared with apes (LCA) to hominids (some, like Marc Verhaegen, claim it continued on through virtually the entire span of human evolution). It claims that certain features are seen in human anatomy and physiology that are only seen in humans and aquatic animals and that these constitute conclusive evidence that our ancestors went through an semiaquatic phase in our evolution. Relying heavily on the principle of convergent evolution, it says that life in an aquatic environment explains these features and that a transition from ape to hominid in a nonaquatic environment cannot. The principle of convergence is used to explain these features, and the idea is said to be more parsimonious than other hypotheses.
Their use of the idea of convergence is generally accurate, but generally, they use parsimony to mean that only one cause explains many features (a more accurate term might be “prime mover” or “umbrella hypothesis,” the latter being one that AAT/H critic John Langdon uses).
One problem with the idea is that most of the proponents have been rather vague about the degree of aquaticness to which they refer. One proponent, doctoral student Algis Kuliukas, has come up with an explanation apparently also now endorsed by Elaine Morgan, that water has acted as more of an agent of selection in human evolution than in the evolution of apes such that physical differences between the two may be at least partly explained as adaptations to more efficient movement through acquatic conditions. This definition is perhaps most notable for its vagueness, merely suggesting “more” water use by humans than by apes. Contrast that with the explanation set forth in by Bininda-Emonds, Gittleman, and Kelly: “We consider aquatic carnivores to be those species in which the aquatic habitat inevitably plays a key role in the life-cycle of an individual,” which they then compare to definitions as given by others as they discuss the strengths and limitations of their own definition. The AAT/H definition suggested is not only so vague as to be virtually meaningless, it is notable that this is the first attempt at such an explicit definition, and it has taken over 40 years to show up. There has always been an implicit “how aquatic” definition, however, ascertained by the characteristics the proponents have used to build their case.
The proponents of the AAT/H have almost always been vague about just how aquatic our ancestors supposedly were, and now tend to say simply those ancestors were “more aquatic” than apes, and often use Alister Hardy’s suggestion that we were less aquatic than otters. Coupled with this, they are often coy about what animals are said to share our “aquatic” features, sometimes simply saying that these features are found in an aquatic setting or that we share these features with “aquatics.” This produces a disconnect between how aquatic most AAT/H proponents claim our ancestors were and what the idea clearly implies on this vital aspect.
The human features said to be accounted for by a semiaquatic past can vary a great deal from one AAT/H account to another, but they form a large and eclectic list, far too large to deal with here (various proponents have suggested sweat, tears, sebaceous glands, the shape of our nose and our thorax, and even being able to cup our hands better than chimps). Probably the most commonly cited features are bipedalism, fat characteristics, and the distribution of human hair. AAT/H proponents concede that bipedalism is not found in any aquatic or semiaquatic mammal. They use a double standard here, as they commonly argue that the idea that hominids evolved bipedality in a terrestrial setting is badly damaged by the fact that no nonhuman terrestrial mammal is predominantly bipedal, yet the fact that no aquatic mammal is bipedal is brushed off as irrelevant.
The mammals with the fat features the AAT/H proponents say are similar to ours are seals, whales, and the sirenia (dugongs and manatees) and for lessened hair, only whales and sirenia and one species of wild pig, the babirusa, which has less hair than other wild pigs and is at home in water but also seems to be, like humans, an exception, since other wild pigs that are at home in the water have plenty of body hair; the babirusa seems to be, like other mammals with lessened body hair (such as some mole rats), an exception among related mammals with similar habits. The pachyderms also have little body hair, and although this is generally accepted as being due to their size and the need for heat loss, this well-established physiological principle concerning volume versus surface area is viewed with suspicion by many AAT/H proponents as they concentrate on water as a guiding factor in evolution. So, the aquatic mammals the proponents say we resemble have all been aquatic for tens of millions of years and are so highly specialized they are virtually, or completely, incapable of living a non-aquatic life. The AAT/H claim that these features arose in a mammal less aquatic than an otter rings hollow.
So, relative fattiness and body hair loss among aquatic species are actually restricted to only a very few highly specialized aquatic mammals. Even more damaging to the AAT/H is that these features in aquatic animals do not actually resemble those of humans in any but the most superficial manner. This has particular significance in light of the AAT/H claim to be more parsimonious than other theories.
Most humans are fatter than many wild mammals, and we have, on average, less body hair than apes and most other wild mammals. But the characteristics of human hair and fat—the differences between the sexes and during the individual’s lifespan—are not like hair and fat features due to convergent evolution due to environment. Instead, those characteristics in humans seem to be classic cases of sexual selection. They differ considerably between the sexes, change dramatically at puberty, and then change again at the end of the reproductive period of life. (We are also unusual in having rather fat babies, but that seems to be connected to the fact that our infancy and accompanying brain growth is itself a highly unusual affair among primates, or any other mammal.) In aquatic mammals, these fat and hair characteristics either start out similar to adults of their species or become like adults of their species very rapidly after birth. This is also true of other features that AAT/H proponents use or have used as evidence, such as sweat and sebaceous glands.
The problem vis-à-vis parsimony is that if these were due to convergence during a semiaquatic past, the AAT/H requires two major changes to these features instead of one: first, ancestral, then similar to aquatic mammals, then sexually selected as in modern humans. Other hypotheses would require only one change, perhaps gradual: first ancestral, then sexually selected, albeit perhaps with some supporting advantages in natural selection (such as Wheeler’s cooling hypothesis or the recent idea that elimination of some parasites had a hand in our present hair characteristics). So, the AAT/H claim to be a more parsimonious explanation for these features falls apart.
Explanations for these discrepancies have been offered. Sometimes proponents actually suggest that the degree of aquaticness in hominids varied between the sexes and during the lifespan, so as to match the characteristics we see today. Since both sebaceous glands and hair are used as evidence, the hypothesis becomes internally inconsistent, since then females would have to be more aquatic than males to explain hair and body fat, while males would have to be more aquatic than females to explain sebaceous glands; babies would be aquatic to explain hair and body fat, but not very aquatic to explain sweat and sebaceous glands, while these same characteristics in children would mean they were relatively nonaquatic until puberty. These ad hoc explanations seem much more unlikely than the simple explanation of sexual selection.
There are other problems with AAT/H attempts to explain human hair as the result of some degree of aquaticness. The only reasonable suggestion as to why body hair would be reduced is to aid in swimming speed (some take the tack that it just is similar to aquatic mammals and offer no reason for the similarity— however, as mentioned already, it is not really similar). There is, however, conflicting evidence on body hair and swimming speed; it would seem that increasing body hair might work as well as eliminating it, but humans took neither course. We still have body hair, and many humans have quite a lot of it, often curly and just what we don’t want for increased swimming speed. That is why competitive swimmers use one or both of two methods—they shave off body hair and recently many have adopted special body suits that increase boundary layer thickness and decrease drag by mimicking the effects of dermal ridges as seen in dolphins’ skin or the hair of seals. The one thing competitive swimmers don’t want is what we have now, yet what we have now is what AAT/H proponents say was due to adaptation for swimming speed. And then there is the hair on our heads, which is far longer, and often bushier, than that of apes. So, the AAT/H proponents are left with several ad hoc explanations They have suggested that head hair is explained by a swimming stroke, usually said to be the breast stroke, which leaves the long head hair (and beard in males) entirely out of the water—and this unlikely position is supposed to be one which allows for high swimming speeds creating selection for hair loss. Otherwise, they are faced with claiming that there was intense environmental selective pressure for reduction of body hair but not for head hair. The only other explanation would be that there were two major changes to hair instead of one as required for nonaquatic hypotheses, which destroys their claim of parsimony.
The problem of likely aquatic predators such as crocodiles and sharks being much faster swimmers than even the best human athletes today is met with the suggestion that we congregated in large groups and the aquatic predators would only catch the slower members. This is unlikely to have helped even if true, since aquatic predators are seldom seen before they strike and would not have to take the slowest swimmers even if the herding idea was true. Still, that is better than Morgan’s first attempt to answer the problem of crocodiles, which was to label them “hypothetical.” No credible suggestion of how these ancestors would meet the problem of aquatic predators has ever been produced. Another problem for the hypothesis is the fact that while terrestrially we can show how an animal of medium size with a low birthrate can, and still does, deal with predators, by studying chimpanzees, no aquatic or semiaquatic animal of medium size with a low birthrate exists.
A common argument for the AAT/H over the years has been the fact that many humans like to visit the seashore, and many humans like to swim for recreation. This race memory argument has been used by both Hardy and Morgan (Hardy in particular believed in the race memory idea as part of his long-held belief that race memories and telepathy had played a role in human evolution) and carries no more weight, and perhaps less, than Gordon Orians’s idea that our liking for certain park settings is based on our evolutionary past on mixed savannas. Lately, the subject of fatty acids for brain growth, specifically DHA and LNA, have been promoted as support for the idea of an aquatic past, since marine fish, especially cold-water marine fish, are rich in DHA. This ignores the fact that these fatty acids are readily available in various plant sources as well as in wild game. Humans (except infants) can synthesize DHA from LNA found in plant foods; infants get it through breast milk.
Some evidence long used as support for the AAT/H has been dropped by its proponents, such as Morgan’s contention that sweat and tears were analogous to salt excretion glands, as seen in marine and desert reptiles and birds. The problem here is that even when this notion was first put forward, it ran counter to basic physiological principles in osmoregulation, including the fact that such excretions are never hypertonic, as they would have to be to be part of such a system. When Morgan formally dropped this line of evidence, she claimed it was because new information had been discovered that wasn’t available when she first proposed it, but in fact the contrary information was known well before she first brought it up, and some of that information was in the references she used as the sources for her claims. This does not speak well of the reliability of AAT/H research, and is not unusual.
Morgan has used a passage about bradycardia in seals, the slowing of the heart, as evidence about breath holding before dives. Morgan has also incorrectly stated that hymens are only found in humans and aquatic mammals; that humans, bonobos, and aquatic mammals are the only ones that engage in ventro-ven-tro copulation; that seals sweat via eccrine glands; that the only nonhuman animals that have been reported— none confirmed—to cry emotional tears are aquatic ones (information to the contrary was in the same book and chapter Morgan used as a source); and that the predominate mode of terrestrial locomotion of proboscis monkeys is bipedal. Morgan also has proved to exhibit something of a free hand when it comes to quotes in some of her AAT/H accounts, leaving out words or context to change their meaning, often with-out indicating the words are absent.
Marc Verhaegen has a history of dubious research. For example, he has claimed that sea lions are, after humans, the mammals that use sweat cooling the most, but in fact sea lions’ sweating mechanisms are not very efficient at all, unlike those of a variety of terrestrial mammals—that information was in sources that he referenced. Verhaegen has also suggested that Neandertal noses acted as snorkels and that ear canal exotoses, seen in a small number of Neandertal and erectus specimens, can only mean they were doing a great deal of swimming and diving. Problems with this are that such exotoses also result from exposure to cold air without swimming or diving, and it seems that a pathological condition would be weeded out in a species that was long adapted for swimming and diving. Other examples of the quality of his research include his description of the rhinoceros as “predominantly aquatic” and using the mountain beaver as an example of an aquatic mammal, apparently confused by the name (the mountain beaver often likes wet areas and burrows and succulent plants, but dampness does not make one aquatic in any realistic sense).
These are far from the only examples of poor AAT/H research, and unfortunately they typify the quality of research one sees when the idea is examined closely.
In recent years, proponents have paid a great deal of attention to the research on chimpanzees and gorillas that wade, along with any information about bonobos wading. This is an abrupt about-face, since as late as the mid-1990s, most were claiming as evidence the “fact” that common chimpanzees avoided water at all costs (a common misconception disproved well before that). The amount of bipedality in these situations is often wildly overstated by proponents, and another problem the AAT/H faces with these and other primate species that wade or swim regularly is that these species don’t exhibit the other changes the AAT/H predicts—changes such as fat and lessened body hair—but this problem is either downplayed or ignored. It is interesting that bonobos and other apes sometimes use bipedality when wading, and it is certainly one of the items on the list of things that apes sometimes use bipedality while doing, but the AAT/H attempts to be far more than one item on a list.
In summary, the AAT/H has been in existence for well over 40 years now, and while it has certainly attracted a following, it hasn’t been very convincing to most anthropologists who’ve looked at it closely. Its proponents tend to use to their advantage the fact that most people accept the proponents’ accounts of the features mentioned and assume that the proponents have been somewhat rigorous and honest in testing their theory against the evidence. And few people are conversant with all the varied lines of evidence that its proponents use. Perhaps a greater problem is that most people accept the proponents’ claim that they are doing no more than suggesting that humans used water somewhat more than apes during the evolution of our species—certainly a noncontroversial claim, but a disingenuous one as well when you see what features the AAT/H claims as evidence.
- Bininda-Emonds, O. R. P., Gittleman, J. L., & Kelly, K. (2001). Flippers versus feet: Comparative trends in aquatic and non-aquatic carnivores. Journal of Animal Ecology, 70, 386-400.
- Morgan, E. (1990). The scars of evolution.London: Souvenir Press.
- Morgan, E. (1997). The aquatic ape hypothesis. London: Souvenir Press.
- Roede, M., Wind, J., Patrick, J. M., & Reynolds, V.(Eds.). (1991). The aquatic ape: Fact or fiction?London: Souvenir Press.