You may have noticed some coverage in the press recently about the Aquatic Ape Hypothesis (AAH), sparked by a conference on the topic due to be held in May.
If you’re not familiar with the AAH it basically suggests that human ancestors passed through a semiaquatic stage which provided the selective pressure that has led to the differences seen between humans and other primates. Some people call it the Aquatic Ape Theory, but it lacks the necessary scientific support to be considered a theory so it remains a hypothesis [see comments for discussion of the terminology].
The idea was first suggested by pathologist Max Westenhöfer in 1942 and the first line of evidence in support of the hypothesis was proposed by marine biologist Alister Hardy in 1960. Hardy noted that subcutaneous fat is unusual in terrestrial mammals and is normally associated with marine mammals – raising the very good question ‘why do humans have subcutaneous fat?’ (the answer being because we eat too much and exercise too little – just like some lab monkeys).
The baton was then picked up by writer Elaine Morgan who has championed the AAH since 1972. Here’s Elaine in action on a TED video from 2009:
Elaine Morgan is a great communicator and she’s done a remarkable job of delivering the AAH to a wide audience, but I have concerns that the packaging is more impressive than the contents, from a scientific perspective.
In the video Elaine does a cracking job of setting up the AAH in opposition to the more established Savanna Hypothesis (SavH), which suggests that humans diverged from other primates as a result of exploiting more arid environments. She then suggests that the SavH has been discounted on the basis of palaeoenvironmental data, leaving a paradigm gap that should (she suggests) be filled by the AAH.
But of course, a paradigm gap should only be filled by a robust theory and when it comes to plotting evolutionary trajectories there is not solid theoretical foundation on how to do it, beyond relying on the physical evidence provided by the fossil record.
In this case that would require fossils of human ancestors to be found in primarily aquatic deposits, something which we do not see, which is surprising, since aquatic environments are usually far better for fossil preservation than terrestrial environments. In fact, taphonomy suggests that early hominid fossils would be more common if the individuals were living and dying in water with any frequency.
Without having physical data in the form of fossils linking hominids to water, it becomes difficult to make a connection without falling back on evolutionary ‘just-so stories‘, that try to explain an observation by relying on a plausible narrative.
The trouble with this is that the public and media love a good narrative, but it simply isn’t scientific unless it can be falsified. I think this is the part of the process that Elaine Morgan doesn’t quite grasp – she is convinced by her own narrative and believes in the hypothesis, but for a scientist it is more appropriate to subscribe to none of the available hypotheses if they cannot provide factual evidence in support. This is where I currently stand.
I am certainly not convinced by statements like:
“Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is found in large amounts in seafood,… It boosts brain growth in mammals. That is why a dolphin has a much bigger brain than a zebra, though they have roughly the same body sizes. The dolphin has a diet rich in DHA. The crucial point is that without a high DHA diet from seafood we could not have developed our big brains. We got smart from eating fish and living in water.” [Quote attributed to Dr Michael Crawford]
This statement starts by comparing two utterly different species, with a very different evolutionary history and current mode of life, then offers a single dietary explanation for the difference in brain size. This is patently nonsense.
If a seafood diet is the main driver of large brain size then the relatively very large brains of Chimpanzees and other Apes become a remarkable oddity and the relatively small brains of Blue Whales become bizarre variants. Moreover, what about people that don’t have access to seafood? Are they unable to grow large brains? No. Clearly there is more going on.
Brain size is not directly linked to a single dietary chemical, it is linked to managing interactions in and with a complex environment – keeping track of seasonal and spatial variation in fruiting or schooling of fish, coordinating group efforts and understanding prey behaviour to hunt more effectively, or problem solving to access food sources that are hard to acquire. Where a big brain provides a selective advantage, it will evolve.
I don’t want this post to turn into a refutation of the AAH, since there’s a lot to say and much has been done elsewhere. What I do want this post to do is highlight that a scientific theory needs to be testable, it needs to consider contradictory information and it needs to be aware of confirmation bias.
The AAH relies strongly on observed similarities in condition between humans and aquatic mammals, but it dismisses other similarities out of hand. For instance, Naked Mole-rats are simply dismissed by Morgan as an example of a non-aquatic mammal that has lost body hair, but they provide evidence that hair loss can occur for reasons beyond aquatic adaptations – which is worthy of note.
It is also worth considering the supporting examples in the context of phylogeny and physiology, which doesn’t seem to happen often. For instance, the Cetacea, walruses and Sirenia are examples of naked aquatic mammals cited in the AAH, but both the Sirenia and walruses retain a short coat of hairs, quite different in structure to the fine body hair of humans. Whales and Sirenia have also been adapting to an aquatic habitat for 50 million years and the ‘nakedness’ of modern examples may be more related to the evolution of large body size and the benefits to thermoregulation provided by mass – which is supported by the fact that the largest species in the Pinnipedia (like the Elephant Seal and Walrus) are much less reliant on fur than the smaller species of seal.
Unless our ancestors were massive, it seems unlikely that they would have been losing their hair in order to survive better in the water.
Of course, that’s not to say that our ancestors avoided water – far from it. Marginal environments are rich sources of food and most terrestrial animals that live near water will exploit it in some way or another. I’m sure our ancestors would have done the same, I’m just unsure about how immersive and influential that exploitation was on our evolutionary trajectory.
So far I am unconvinced by the AAH and the more bad science and overstated arguments I see in support of it, the less convinced I become. Let’s see if any good supporting science with hard facts emerge from the conference in May.
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I’d be happier at all the criticisms thrown at the AAH if the same people were seen to also criticise the less defensible SavH. In their silence they scoff at an idea that raises valid questions and lend support to one that hides them instead.
I don’t think many people care about either SavH or AAH until bad science starts getting presented as fact, that’s what gets the critics going. The recent flurry of publicity around AAH is the reason why the criticism has started up again, the same thing happens when someone publishes something on evolutionary psychology that draws on SavH. It’s all conjecture and it shouldn’t be presented as anything but.
You have to distinguish between the environmentally deterministic Savanna Hypothesis, and the demonstrable fact that human ancestors did live in savannas.
The Savanna Hypothesis is sort of like the savanna version of the aquatic ape theory. It says that all the traits that distinguish humans from other apes emerged BECAUSE we evolved on the savannah: We have language because the savannah necessitated it, we have tool use because the savannah necessitated it, we’re bipedal because the savannah necessitated it, we became hunters and meat-eaters because the savannah necessitated it, etc. Obviously, this is just-so story telling in the same vein as the AAT.
However, it is true that all known or suspected human ancestors lived in open woodland, wooded grassland, or grassland, collectively known as “savannas”. (Woody cover and hominin environments in the past 6 million years, Cerling et al; Nature, 2011)
People who are wary of the Savanna Hypothesis sometimes make the mistake of assuming that the FACT that our ancestors demonstrably DID live in savannas is equivalent to the Savannah Hypothesis. It’s not. Yes, our ancestors did live in savannas. This is demonstrable fact. No, this doesn’t mean that everything that distinguishes us from the other apes was an environmentally deterministic outcome of having lived on the savanna.
Other people have heard that the Savanna Hypothesis is “dead”, and they mistaken believe that this means human ancestors didn’t live in savannas. Wrong. Human ancestors DID live in savannas. This can be demonstrated beyond the doubt of a reasonable person. When we say the Savanna Hypothesis is “dead” we’re not saying that humans lived and evolved elsewhere. What we’re saying is that we don’t assume that human evolution was an environmentally deterministic outcome of having lived in savannas, where we know human ancestors did live.
If you’re saying that the notion that our ancestors over the past 6 million years lived in savannas is “less defensible” than the notion that they lived in rivers, lakes, and the ocean, you are mistaken. All of the available evidence places our ancestors in open woodland, wooded grassland, and grassland. Every fossil. Every artifact. On the other hand, there is literally zero evidence placing any human ancestor as a regular inhabitant of any aquatic environment. Zero. None.
Well….our ancestors lived in ground that is savanna TODAY.
That does not mean they lived on savanna.
Gani MR, Gani ND, River-margin habitat of Ardipithecus ramidus at Aramis, Ethiopia 4.4 million years ago. Nature Communications :1-5, (2011). Hardly savannah.
Thanks, MJ. OHSU said: “the demonstrable fact that human ancestors did live in savannas.” ?? Which “human ancestors” you mean, OHSU? Lucy? Lucy was no human ancestor, and moreover did not “live in savannas” but was found amid crab claws & crocodile eggs (R.Leakey). The same for all so-called “human ancestors”. Australopiths lived in wetlands (K.Reed): even if they were “human ancestors” (which they’re not IMO) & if they “lived in savannas”, it was in the wetlands & gallery forests & lagoons of “savannas”. But the littoral theory is not about australopiths, but about Pleistocene Homo, who dispersed to different continents (Africa, Europe, Asia) & islands (e.g. Flores & Crete) along the coasts, of course (how else do you read Flores or crete?), not running over “savannas”! Besides, sweat = water + salt = scarce in savanna. Archaic Homo dispersed (probably early-Pleistocene, possibly late-Pliocene) along coasts & then rivers, beach-combing, diving & wading bipedally for littoral, shallow-aquatic & waterside foods, incl.shellfish, richest in brain-specific nutrients such as DHA, taurine, iodine etc. The savanna idea is dead, but most followers still don’t realise this. Please inform properly & with open mind, e.g. google: original econiche Homo.
This statement in the opening paragraph…
“Some people call it the Aquatic Ape Theory, but it lacks the necessary scientific support to be considered a theory so it remains a hypothesis.”
… betrays a fundamental misunderstanding on the part of the author. Hypotheses don’t graduate to theories once someone provides evidence in their favor.
For some reason a very large number of people falsely believe that there is a chain of progression from hypothesis to theory to law, something like this:
Hypothesis. Basically empty conjecture.
Theory. Used to be a hypothesis, but then someone supported it with evidence, and it graduated to the level of “theory”.
Law. Used to be a theory, but then it was proven true and it became a law.
Of course scientists and science-minded people learn somewhere along the line that theories don’t become laws (especially those who follow the evolution/creationsim debate and learn the “it’s just a theory” fallacy), but a huge number of them continue to believe that hypotheses do become theories. They don’t! The hypothesis-to-theory idea is just as wrong as the theory-to-law idea.
The major difference between a hypothesis and a theory is scope. You can think of a hypothesis as a mini theory. A hypothesis is a proposed explanation for a single observation (or a portion of an observation, or a limited range of similar observations), while a theory is a proposed explanation for a large number of overlapping observations and provides an explanatory framework for many facts, observations, hypotheses, axioms, and laws.
The Aquatic Ape THEORY is large enough in scope to be called a theory. Each of the individual claims is small enough in scope to be called a hypothesis (“wading hypothesis”, “hair/drag hypothesis”, “fat/buoyancy hypothesis”, etc.). The Aquatic Ape THEORY fails as a scientific theory because it has no supporting evidence. BUT ITS LACK OF SUPPORTING EVIDENCE DOESN’T DEMOTE IT FROM A THEORY TO A HYPOTHESIS, it demotes it from science to pseudoscience.
The correct term isn’t the “Aquatic Ape Hypothesis”, it’s the “Aquatic Ape Pseudo-Theory”.
I’m frustrated with how poorly people understand basic scientific ideas, vocabulary, and methodology.
I understand the difference, I just wanted to get to the subject matter I was interested in rather than writing about the difference between a hypothesis and a theory – both of which are commonly used in reference to this pseudotheory. I wanted to make sure both terms got a mention so the article would get picked up by Google when people search for the term. I admit it was lazy, but thankfully you’ve highlighted the proper use of the terms for me, so many thanks.
You’re welcome. Sorry for the rant. I like your blog.
As an elaboration of my comment above, a discussion of laws, hypotheses, and theories:
Scientific Law: A scientific law is an observation about the relationship between two or more variables. In general, scientific laws are couched in mathematical terms.
One example is the Boyle-Mariotte Law that relates the volume and pressure of gasses maintained at constant temperature. It essentially says that volume and pressure are inversely proportional. It is expressed as PV = k
Scientific laws don’t attempt to explain the reason for a particular observation. They merely lay out the details of the observation, usually with great precision and in mathematical terms.
Hypothesis: A hypothesis is a tentative explanation for a given observation. In order to be considered scientific, a hypothesis must be falsifiable. In other words, there must be some observation which could potentially disprove the hypothesis. (If you cannot imagine a piece of information which, if discovered, would disprove your hypothesis, then it isn’t scientific.)
For example, we might hypothesize that the reason for the Boyle-Mariotte Law is that gasses are made up of tiny particles that are bouncing around in constant motion. We might hypothesize that at a given temperature they naturally assume a particular volume corresponding with their kinetic energy. There are many experiments that could potentially confirm or refute this hypothesis.
Theory: A theory is a robust, systematic explanation for many related phenomena. Normally a theory is comprised of observations, axioms, postulates, laws, and hypotheses that have been confirmed (failed to be falsified) after years of experimentation. One of the most important features of theories is that they make predictions that are subject to observation and experimentation.
For example, Atomic Theory doesn’t only explain the Boyel-Mariotte law and agree with the hypothesis that gases are made up of molecules, but it explains thousands of observations derived from chemistry and physics. It provides a meaningful reference frame for the laws of thermodynamics, the law of conservation of mass, etc. Literally millions of experiments have been performed in chemistry and physics labs around the world that could have refuted Atomic Theory, and the result is always confirmation of the theory (or failure to falsify). Moreover, Atomic Theory makes specific predictions that can be subjected to new experiments.
As it stands, the AAT is accurately-enough labeled as a “theory”, but it is crackpot theory and not a real scientific theory because it isn’t comprised of robust testable scientific hypotheses and isn’t supported by any genuine evidence.
If you don’t want to call it a theory because you hold special reverence for the word “theory” as scientists use it, then fine. But it is no more accurate to call it a “hypothesis”.
Sorry, again, for coming across as confrontational. Good blog.
No problem – the pedant in me gets annoyed by the same sort of things!
There is nothing unusual about primates exploiting aquatic resources for food. Wading bipedally in shallow water and even diving underwater for aquatic plants or shellfish in freshwater and in marine environments has been observed in many monkeys and apes and, of course, is common in primitive human populations. So its certainly not a question as to whether such bipedal aquatic feeding behavior in humans and other primates is possible.
The question is, is there any evidence that a primate species actually became– specialized– in such aquatic feeding behavior for an extensive period of evolutionary time and whether its possible humans could be descended from such primates.
The aquatic ape hypothesis was first conceived by Oxford marine biologist, Sir Alister Hardy, back in the 1920s. But he didn’t reveal his hypothesis to the public until 1960 during a lecture and then in an article in the journal, New Scientist.
Elaine Morgan first encountered the hypothesis after she read a synopsis of it in the Desmond Morris book, the Naked Ape. Then she wrote about it in her own book, the Descent of Woman in the early 1970s.
Basically, Hardy’s argument was that humans became bipeds and developed a thick subcutaneous fat because they needed to wade into shallow water in order to get access to shellfish.
I should note that aquatic wading is also one of the leading hypotheses for the origin of bipedalism in archosaurs (dinosaurs, birds, and crocodilians)
I think its pretty obvious that Oreopithecus evolved its bipedalism as a wading adaptation for exploiting aquatic plants during its 2 million years of isolation on the ancient Mediterranean island of Tuscany-Sardinia.
The lobulated medulla of the human kidney strongly suggest that humans were once specialized in consuming foods with an extremely high salt content. Since the African continent tends to be deficient in food resources with high levels of salt, human ancestors obviously evolved such kidneys along a marine coastline.
The fact that humans evolved particular characteristics for the same reasons that most other animals evolve those same characteristics really shouldn’t be all that surprising, IMO.
Marcel F. Williams
“The question is, is there any evidence that a primate species actually became– specialized– in such aquatic feeding behavior for an extensive period of evolutionary time and whether its possible humans could be descended from such primates.”
1. Subcutaneous fat is present in other non-aquatic mammals (brown bears for example). It provides a store of energy that is important in an environment with seasonally abundant but unreliable resources. Even mammals that don’t usually have thick layers of it in the wild will develop it in captivity (including plenty of documented cases in orangutans and macaques). Humans probably just have more of it on a persistent basis than other species because we have ready access to resources.
2. A lobulated medulla can also be explained by humans having a diet with more meat in it than other primates. Several terrestrial species of carnivorous mammal and bird have similar adaptations for dealing with dietary salt. In fact, some arid environment species also have similar adaptations – like the active nasal glands in the ostrich.
3. “the leading theory” and “I think its pretty obvious” provide no evidence.
So in answer to the question posed, there is no unequivocal evidence that a primate species became specialised in an aquatic feeding behaviour.
Humans have an exceptionally thick layer of subcutaneous fat beneath their skin as most primatologist who have skinned both, will tell you. I believe that subcutaneous fat comprises about 9 or 10% of the body weight of a healthy female chimpanzee while it comprises about 29% of the body weight of a healthy human female. Fat is a substantially better insulator in water than hair is.
Bears are phylogenetically most closely related to the pinnipeds (seals and sealions) and some of the earliest bears like Kolponomos were marine adapted. Bears are also similar to the pinnipeds in having multipyramidal kidneys. The marine polar bear has the most pyramids in its kidneys amongst bears.
Lobulated kidneys are not related to meat eating, they’re related to enhancing salt excretion. They are universal in marine mammals and are found in both faunivorous marine mammals and in plant eating marine mammals.
Marine Adaptations in Human Kidneys:
Morphological evidence of marine adaptations in human kidneys.
Med Hypotheses. 2006;66(2):247-57. Epub 2005 Nov 2.
Il rene parla: l’uomo viene dal mare (translation: The kidney speaks: man comes from the sea)
SALVATORE ROCCA ROSSETTI
Professore Emerito di Urologia, Università di Torino
LETTURA MAGISTRALE Urologia / Vol. 74 no. 2, S-7 2007 / pp. S1-5
12 OTTOBRE 2006, TORINO
And as I stated earlier, the bipdal oreopithecines were obviously semiaquatically adapted:
From Harrison & Rook, Function, Phylogeny, and Fossils: Miocence Hominoid Evolution and Adaptations. 1997:
“The remains of Oreopithecus bambolii are extremely abundant in VI, and this species represents one of the commonest mammals at the site…..Evidence for a primarily aquatic setting and a humid forested environment is provided by the extensive lignite accumulations, the common occurrence of skeletal remains in anatomical connection, the abundance of fossil crocodiles, chelonians, and freshwater mollusks, and the occurrence of otters…..The area was evidently poorly drained, and the forested areas were interspersed with numerous freshwater pools and shallow lakes.” pg 335
“Interestingly, there is also a corresponding decline in the abundance of Oreopithecus in V2, which might simply imply a relatively narrow ecological preference by this taxon for swampy, forested habitats.” pg. 336
“Another possibility is that Oreopithecus was exploiting aquatic or wetland plants, such as water lilies, reeds, sedges, cattail, pond weeds, horsetails, and stoneworts, all of which are abundantly represented in the pollen spectrum from Baccinello.” pg. 341,
The AAH relies on extrapolation from functional analogues between taxa that have evolved in response to adaptive pressures. But it seems to assume that humans have not adapted to the non-aquatic environment they’ve inhabited for millions of years.
1) Body fat – find me a healthy human who spends a significant proportion of their time climbing who also has a high percentage of body fat. Seriously – go on a climbing forum to the women’s area and look at the discussions about body fat percentage – they tend to be in the 17-18% range. Low body fat levels in arboreal and scansorial primates can be explained as a selective advantage for climbing. High fat levels in living humans CANNOT be explained as an adaptation to an aquatic environment, since modern humans DO NOT LIVE in an aquatic environment, so the thick layer of fat loses any selective advantage and would be lost if that was the reason for having it. There is no logical reason for Homo sapiens to retain thick fat layers under the AAH.
2) Kidney lobulation in modern Homo sapiens is a foetal condition that sometimes persists into adulthood and is sometimes triggered in adults by an infection. It also occurs in a wide variety of other taxa. My point about the kidney was not about the organ though. It was about functional analogues (which AAH depends on, so they are valid to raise here). In arid-environment raptors and ostriches there are salt excretory mechanisms normally associated with aquatic birds. This demonstrates that functional adaptations for one environment are not necessarily restricted to that environment and that salt excretion mechanisms are useful in arid environments. But this is beside the point – modern humans are not aquatic and our salt excretory mechanisms may be a recent adaptation to the introduction of processed salt in our diet.
I have no problem with the idea that early hominins would have exploited wetland habitats – they’re rich in resources, so I’d be surprised if they didn’t. What I have a problem with is the assumption that a suite of human adaptations are trying to be explained very simply and without any logical consistency.
Fat makes you heavier and slower. And this is particularly disadvantageous for a bipedal species that is already slow of foot because it has to carry its entire body weight on just two legs. And it is also extremely dangerous for a species that emerged in a tropical area with some of the top predators on Earth. Baboons, gorillas, and geladas spend practically all of their time on the ground and have not significantly increased their subcutaneous fat layer.
Humans have retained their insulating layer of fat from their aquatic phase because during that phase, they also dramatically reduced the the length of the insulating hair on most of their body. Humans still need insulation in order to reduce heat loss.
The medullary region of the human kidney is naturally multipyramidal. No other Catarrhine primate possesses a lobulated medulla in their kidneys. And the human kidney normally possesses 8-18 medullary pyramids, again, something not seen in apes or other Catarrhine primates.
An the salt excretory mechanism of humans is clearly not of recent acquisition since there appears to be strong selection pressure to reduce salt loss in the human body rather than to enhance it. A significant percentage of sweat glands on the human body are no longer functional. And those that are functional are equipped with a veins that actually return salt back to the body. Sub-Saharan populations tend to sweat more than Europeans because of the heat, but the salt content is lower.
Again, there is nothing unnatural about primates exploiting wetland environments. Some gorilla species frequently wade bidedally into swamps to access aquatic plants when the fruiting season is over. Some even use walking sticks. Oreopithecus, however, appears to have been a specialist at exploiting aquatic plants. And I believe that the fossil evidence clearly shows that Oreopithecus was the first bipedal hominin.
Marcel F. Williams
Being bipedal doesn’t make humans slower. Humans have the same top speed as a chimp and over long distances they can outrun a horse.
Humans still have body hair, with some populations having more than others and individuals showing huge variation. If thermoregulation was a priority and if fat carries the disadvantages to locomotion that you suggest, you would expect a rapid reappearance of denser body hair in hominins, particularly since fat layers wax and wane according to resource availability. Anyway, the fat distribution in humans wouldn’t provide much insulation for wading, since the lower legs are extremities that would be in contact with the water, yet subcutaneous fat doesn’t tend to be distributed in that area. This makes no sense for an aquatic biped. You would expect reduction in the extremities and a thicker fat layer where heat loss is more pronounced. Maybe our ancestors waded, but that doesn’t make them aquatic.
Again, you’re focussing on one feature of the kidneys in comparison to other primates, without considering functional analogues in other taxa. How a species responds to a selective pressure will vary according to preadaptations and chance mutations. Function is key (as the AAH would have it) and there are no good analogues to humans. But regardless, I’ve already acknowledged that our hominin ancestors would probably have utilised aquatic resources – much like the crab-eating raccoon perhaps. Ingesting lots of salt and/or seafood doesn’t mean that there was an aquatic stage in hominin evolution, since it’s available on the shore (just ask Procyon cancrivorus).
As to sweat glands, humans have an interesting condition regarding them – they allow us to lose heat very efficiently. Not usually a requirement for an aquatic animal.
But the trouble once again is that there is the issue of considering the modern human condition without appreciating that Homo sapiens is very evidently not aquatic and our current adaptations have arisen for a very different environment. There is NO EVIDENCE that our ancestors were naked and there’s NO EVIDENCE that subcutaneous body fat was present in elevated levels in our primate ancestors. In fact I doubt that even Archaic Homo sapiens had body fat percentages close to what we have today – indeed, what’s the average body fat level for a modern hunter-gatherer? Because that’s the level we should be looking at when making comparisons between humans and other species.
“I should note that aquatic wading is also one of the leading hypotheses for the origin of bipedalism in archosaurs.”
Do you have a reference for that? My understanding is that the origin of bipedalism in archosaurs is usually associated with running, and that the amphibous offshoots among stem-archosaurs (parasuchians, proterochampsids) are actually *more* quadrupedal than basal archosaurs, which are terrestrial (ornithosuchids, lagosuchids, etc.)
“Being bipedal doesn’t make humans slower. Humans have the same top speed as a chimp and over long distances they can outrun a horse.”
Its simple physics. Trying to support a structure with for limbs is easier than trying to support it with just two.
“Humans still have body hair, with some populations having more than others and individuals showing huge variation. If thermoregulation was a priority and if fat carries the disadvantages to locomotion that you suggest, you would expect a rapid reappearance of denser body hair in hominins,”
Natural selection works with what it has, not what we wish it had. People in tropical areas tend to be leaner, less fat, than those in tropical areas– unless those tropical populations frequently exploit aquatic resources. European populations do tend to have higher body hair density, but this is probably related to the need to increase head hair and facial hair in colder environments.
“Anyway, the fat distribution in humans wouldn’t provide much insulation for wading, since the lower legs are extremities that would be in contact with the water, yet subcutaneous fat doesn’t tend to be distributed in that area. This makes no sense for an aquatic biped. You would expect reduction in the extremities and a thicker fat layer where heat loss is more pronounced. Maybe our ancestors waded, but that doesn’t make them aquatic.”
It just makes them semiaquatic. The title of Hardy’s original paper was, “Was man more aquatic in the past?”
Wading for food, especially for aquatic plants, usually requires wading into water waste or neck deep. Picking up shell fish with a precision grip often requires submerging your head in order to probe benthic invertebrates. Monkeys that exploit shellfish wade, swim, and dive for such food items. And increasing body fat is almost always beneficial in an aquatic environment because it reduces heat loss. Most the food that endothermic animals eat is not for tissue maintenance, its for the production of heat. Losing too much eat, requires the consumption of more food. And in environments where there may be limited resources, that could be significantly disadvantageous. But one reason I don’t like eating aquatic birds like ducks is because ducks have too much fat on their bodies:-0
“Again, you’re focussing on one feature of the kidneys in comparison to other primates, without considering functional analogues in other taxa.”
In the papers and chapters that I’ve published on the subject, I’ve compared all mammalian taxa.
“Ingesting lots of salt and/or seafood doesn’t mean that there was an aquatic stage in hominin evolution, since it’s available on the shore (just ask Procyon cancrivorus).”
As long as there are significant fresh water resources, it is unlikely, IMO, that humans would evolve kidneys with an exceptional ability to excrete salt. The dramatic lobulation of the medullary region of the human kidney suggest that humans once lived in an environment where salt was plentiful but where fresh water resources were extremely difficult to access. That’s why I believe humans evolved their marine mammal-like kidneys on a small island off the coast of Africa.
And there is genetic evidence suggesting an island origin in human ancestry. Humans have lost a dramatic amount of their genetic variation relative to other hominoids. In fact, some studies suggest that the founding population may have been as small as only a few thousand. A small hominin population trapped on a small island would explain the dramatic loss in genetic variation in humans relative to chimpanzees, gorillas, and orangutans. Also, humans somehow avoided contact with baboons for at least a couple million years. Baboons are found practically all over Africa. But after baboons diverged from the gelada, they spread a retrovirus that heavily infected every primate in Africa, including apes. Yet humans appear to have had little exposure to the virus, showing meager levels of exposure similar apes that don’t live in Africa like Orangutans and gibbons who live in Asia. This has led some researchers to suggest that the origin of Homo was not in Africa but in Eurasia. But it leads me to believe that the origin of Homo was on a coastal island, isolated from the African continent. Homo suddenly appears in the fossil record with its tools after sea levels began to fall dramatically around the world 2.6 million years ago, a time when many coastal African islands would have become part of the African continent. This would mean the hominins went through two semiaquatic phases: one during the Miocene on Tuscany-Sardinia island for about 2 million years and a second semiaquatic phase on a island off the coast of Africa which I believe was probably in the Red Sea area of the northern Afar. The northern Afar was flooded by marine waters during the Pliocene turning some areas into small islands.
Seriously? Do a fact check for human and chimpanzee top speeds. They are the same. Bipedalism is energetically efficient due to energy recovery from the Achilles tendon and the pendulum action of the legs in the stride sequence, which also reduces energy used in muscle contractions during the leg swing. That’s basic biomechanics. Bipedalism is more unstable than qudrupedalism, but that doesn’t make it less efficient – far from it.
What is more efficient when on all fours is picking things up from the ground, or a riverbed. Do a google image search for “collecting shells on the beach” and tell me what proportion of people are standing upright. It only makes sense to be bipedal if you’re wading through water to get somewhere else, it makes no sense if you are collecting a resource from an environment where you need to constantly bend down – as anyone with a lumbar problem will tell you. Having grasping toes would be useful though – you wouldn’t need to bend over if you retained them, you’d pick things up with your feet – like I do with my discarded socks to save my back.
But enough of the speculation about what would ‘work’ for a hominin in a watery environment – it’s pointless since it’s nothing more than vague hand-waving. Lets just look at one ‘fact’ that is crucial to the AAH – the body fat question.
Body fat – man vs monkey
Rhesus macaques in labs that are identified as being in the ‘optimal’ weight range have an average body fat content of 25% with individuals in the obese range averaging 42.7% (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3276972/)
Average body fat in Hadza hunter-gatherers averages 13.5% for men and 20% for women. Even in Western populations men average 22.5% and women average 37.9% (http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0040503#pone-0040503-t001)
There is no evidence for there being a notable difference in body fat percentages between humans and macaques, beyond those imposed by immediate environmental factors. This shows the founding observation of the AAH to be incorrect.
Good counter point. I’m surprised that their fat continent is that high. But on the other hand, the average male Macaca mulatta weighs only about 5 kilograms, so they have a large surface area relative to the volume of their bodies. Humans are about ten times larger. So humans have a substantially smaller surface area relative to the volume of their bodies which allows them to lose heat a lot less rapidly. So the percentage of body fat in humans should be substantially less than that of the much smaller rhesus. But its not.
A better comparison would be with a primate that is close to the weight of a human.
Marcel F. Williams
How about Orangutans? Hard to find a study with a good sample size (especially one that’s freely available and quick to locate), but with minimal search I found this: http://onlinelibrary.wiley.com/doi/10.1002/ar.21449/full
“The variation among orangutans in the sample perhaps can be attributed to state of health before death and to age changes. Orangutan 1 (BE) although young, was chronically ill, had less muscle (33.9%) and more estimated fat (over 20%) than the other two. Orangutan 3 (BU), also young, died suddenly had more muscle (35.9%) and less estimated fat (15%). Orangutan 4 (JI) was extremely obese, not untypical for captive orangutans; he was old, only 10.6% muscle, and estimated body fat above 45% of total mass.”
So figures for male orangutans range from 15% to 45% compared to an average of 13.5% for human male hunter gather and an average of 22.5% for a Western human male.
Fat mass is related to quality and quantity of food in primates. Gorillas have low fat masses because their diet is low in energy. Orangutans and Macaques have a diet more similar to ours and they have fluctuating fat levels that easily overlap with ours.
This also shows the founding observation of the AAH to be incorrect.
Of course, if you compare obese primates with obese human beings, there would be no comparison.
But the aquatic ape hypothesis is not simply based on one feature but on numerous features. And Hardy’s hypothesis that earliest evidence of bipedalism and the manual precision grip would be found in a semiaquatic ape is pretty much confirmed in the 7.6 million year old aquatic plant eating swamp ape, Oreopithecus bambolii, who evolved both features on the ancient island of Tuscany-Sardinia.
Just to further annoy some of the anti-aquatic ape folks out there, I should note that the 2002 edition of the Encyclopedia of Marine Mammals mentions the marine mammal-like kidneys of humans in its chapter on Kidney, Structure, and Function:-)
Marcel F. Williams
What is worrying is that the founding observation of the AAH was never properly fact checked by the proponents. When presented with counter evidence another line of inquiry is pursued, without addressing the flaws highlighted. This is not how science works and it is not how a theory finds support.
If a theory doesn’t fit the evidence, then that discrepancy needs to be acknowledged and the theory needs to be reassessed in light of the evidence. You can’t just ignore evidence you don’t like and look at something else that might give you better support. Well, I suppose you can, but if you play that game then don’t expect to be taken seriously by the scientific community.
The fossil evidence shows that the earliest bipedal hominoid with a precision grip (Oreopithecus) lived in a wetland environment– just as Alister Hardy predicted.
The anatomical evidence shows that humans are unique amongst all Catarrhine primates in having a kidney like a marine mammal.
Plus there are living models of humans and other primates using bipedalism to exploit aquatic resources.
The aquatic ape hypothesis is popular because it actually shows that human ancestors evolved their characteristics for the same reasons that most other animals evolved them.
The problem that the opponents of the aquatic hypothesis have is that their hypotheses usually have — never been seen in nature– before! And extraordinary hypotheses require extraordinary evidence.
The bipedal exploitation of shellfish and aquatic plants, on the other hand, is seen in many modern human populations and in other primates and has been recorded in the human fossil record since the time of Homo erectus.
Marcel F. Williams
Yes, but Hardy made these predictions when he thought his observation about body fat in primates was accurate. It was not. What you have done is to cherry-pick a few coincidences and ignore the rotten cherries in your basket.
Address the body fat.
It is accurate. Anyone who has human’s closest relatives, the gorilla and the chimpanzee knows that!
Marcel F. Williams
It is demonstrably NOT accurate. It can be shown to be inaccurate by using references to independent research.
Well the anatomist and primatologist who ran the Yerkes Primate Center, Geoffrey Bourne, said it was true in his books written on the subject.
Clearly he didn’t check enough independent literature. Having a comment from an authority simply isn’t good enough, especially when it can be shown to be unfounded.
“Clearly he didn’t check enough independent literature. Having a comment from an authority simply isn’t good enough, especially when it can be shown to be unfounded.”
Yeah. Obviously a man a ran one of the top primate centers in the country and who actually dissected both humans and other apes with his own hands doesn’t know what he’s talking about:-) But you do:-)
Marcel, do you even know what science is? One person’s observation is not enough. It needs verification by independent sources. On examining the readily accessible peer-reviewed research on primate body fat (examples of which have been shared above) the facts clearly do not support Bourne’s individual observation. Appeals to authority aren’t science.
“Marcel, do you even know what science is? ”
Yeah. I know what science is but you clearly don’t.
Marcel F. Williams
I certainly know what a troll is and I appear to be talking to one right now.
“What is worrying is that the founding observation of the AAH was never properly fact checked by the proponents. When presented with counter evidence another line of inquiry is pursued, without addressing the flaws highlighted. This is not how science works and it is not how a theory finds support.”
This would be more encouraging if we’d seen the same level of consideration and self-criticism from people who are skeptical about the idea.
In fact, what has happenned is one-way nit picking and sneering.
Where, for example, is there a paper in the vast palaeoanthropological literature that even considers, let alone rejects, the wading hypothesis of bipedal origins?
The Camridge Encyclopedia of Human Evolution does not even mention the fact that humans have less body hair than our ape cousins, let alone speculate about why.
The key word there is “speculate”. The AAH is pure speculation and there is a poor track record of the proponents critically testing that speculation. That’s not how science works.
Critics are right to nit-pick, because AAH proponents aren’t being critical of their own ideas. Cherry-picking observations to generate a correlation is not good science on several counts – and that describes the entire body of ‘evidence’ I’ve seen for the AAH.
Where specific claims are researched rather than being taken as gospel (for example the body fat observation discussed above) they turn out to unfounded.
Science isn’t some big love-in where support is forthcoming because people like an idea. Science relies on evidence to support ideas. Show me good evidence and I’ll change my mind.
Speculation is the usual intellectual fuel on which science thrives. It is interesting that palaeoanthropologists have deluded themselves that speculation is ok as long as it doesn’t involve the dreaded ‘a’ factor.
I notice that you did not have an answer to my simple, straightforward, question about the science which led to the field rejecting the wading hypothesis – you know, that crazy idea (about as crazy as the idea the universe was created in six days, just for us according to Henry Gee) based upon the observation that the most predictable place our great apes move bipedally is in waist deep water.
Or, do you accept that the “rejection” was made on the basis of no science whatsoever but, instead, a lot of ignorant sneering.
There is a good deal of evidence, most obviously the simple fact that we swim and dive better than chimps. Normally, evolutionary biologists assume that when species a moves better than species b through substrate c, it is due to natural selection. The only exception, as far as I can tell – out of billions – is when a = Homo sapiens, b = Pan/Gorilla and c = water.
Don’t tell me, we swim better than chimps because we’re more intelligent or is it that story about it being due to our bipedalism? And the explanation for our bipedalism? How does that one go? Oh yes, we were always bipedal, right? That’s the latest thinking, isn’t it?
Maybe we swim better than chimps because we’re more gracile and have shorter arms for other reasons – a preadaptation if you will. Apes are odd in terms of their reluctance to swim – many other mammals, including other primates are perfectly good swimmers without having special adaptations for swimming. I expect that extreme forelimb length is probably the main issue for the other apes when it comes to swimming, so should we be surprised that humans are reasonable swimmers when we lack the extremely long arms of our cousins?
Oh and while I agree that speculation is important for framing questions in science, I think it is important that good evidence is presented to support it. Darwin had to put up with a lot of sneering, but the evidence won through – evidence is the key.
Great post, thanks for the information about the Docosahexaenoic acid speculation – I always wondered how that even became considered as evidence.
It’s a prime example of confirmation bias. In fact, thinking about it, the AAH could be adopted as the poster-child for confirmation bias…
The confirmation bias is that exhibited by aquaskeptics who do not have a clue about why humans are so different from chimps but somehow, dogmatically certain that it could not have been due to moving through water. No matter what evidence is presented, they always find an excuse to discount it. It is the very definition of confirmation bias.
Algis, there is no problem with the idea that locomotion through water may have played a role in human evolution. The problem is that the proponents of the AAH have pushed the explanatory power of that idea to extremes that are not warranted and not supported by any good evidence.
AAH proponents have probably done more harm to the idea of bipedalism evolving as a result of wading than any other group.
The wading hypothesis needs to be properly tested, as with any other idea in science – more importantly, even proponents of an idea should be sceptical about it – it’s the process of falsifying ideas that science relies on and it’s hard to do that if you don’t approach an idea with an eye to tearing it down. It’s how Darwin approached natural selection, and that’s why it’s a good and robust theory.
Which “AAH” proponents? What extremes? I don’t think you know what you are talking about? Some of dont even call it the AAH any more. The last scholarly book on the subject included a chapter by Elaine and I that suggested they (because there are more than one) should be called “Waterside Hypotheses of Human Evolution”. Have you read it?
Please back upi the slur about some people doing “more harm” to the idea that wading might have influenced our bipedality? I have had two papers published in the literature on this? Are you referring to those? Have you even read them?
Please point me to any other paper (and there are hundreds to choose from) in the past 150 years where an idea on human evolution was approached from the basis of “tearing it down” or admit you’re just clutching at straws.
Extremes like suggesting that suites of characters in modern humans are a result of an aquatic stage. For example, the presence of subcutaneous fat, loss of body hair, structure of the kidneys, large brain, etc.
As for pointing you to a paper on human evolution that approaches the issue from a scientific perspective, there aren’t any. Most rely on conjecture since evidence is poor. That’s why in my article I state “for a scientist it is more appropriate to subscribe to none of the available hypotheses if they cannot provide factual evidence in support. This is where I currently stand.”
So far I’ve not seem any good support for any single hypothesis explaining the trajectory of human evolution – they all rely too much on conjecture and speculation and are often driven forward using appeals to plausibility and cherry-picked information, whilst ignoring or discounting contradictory information.
It’s the peculiar phenotypical differences between humans and chimps that are extreme (especially considering that chimps are closer, genetically, to us than they are to other species) not the idea that moving through water might help explain them.
So how do you explain them?
Yes, most of the ideas in palaeoanthropology are just so story telling but only waterside hypotheses are derided as being as bad as creationism. I don’t see Lovejoy being tarred with that brush because of his even less plausible just-so story of monogamous pairing and male provisioning. As Dan Dennett said, the arguments against are always so thin and ad hoc.
I have just attended a two-day symposium where a lot of scientific evidence and argumentation was provided in support of the simple idea that selection from moving through and procuring food from water (you know, that stuff that is pretty much everywhere, that we rely on to live, and that changed dramatically through climate change since the Miocene in Africa) could have affected our phenotype. But people like you and Henry Gee seem unable to discriminate between this intellectual efffort to do science and the biggest load of drivel the human mind has ever conceived of. Quite bizarre.
I notice that you didn’t answer positively to my query about you reading the latest scientific literature on the subject. So, I think people must assume that your railing against these ideas are just based on out of date prejudice.
My issues are with the AAH, which is still being circulated and touted in its original form for public consumption (see articles and video cited above). In case you hadn’t noticed this is a blog, not a scientific journal – the intent here is to challenge bad science that gets presented to the public. I don’t do original research on the topic of human evolutionary trajectory (mainly because I think it’s too speculative to be worthwhile), so I keep my mouth shut and my mind open about possible scenarios. What I will open my mouth about is observations that are demonstrably flawed but are used to support scenarios – like the subcutaneous body fat assertion that started the ball rolling on the AAH.
If you have distanced yourself from the old AAH and are refining new hypotheses then good for you. But if that’s the case then I don’t see your problem with me highlighting issues with the AAH as was (since it is still being circulated). I am not the kind to throw the baby out with the bathwater, so I recognise that there may be elements of hominin utilisation of aquatic habitats that may have influenced human evolution, but until I have seen good evidence to support this I will remain sceptical. You mention research that you’ve done on the subject, but you have not provided citations or links to the work – do so and I will take a look.
“They might well have done – it’s just as likely (if not more likely) than human ancestors going through an entirely marine stage”
Note here the pseudoskeptic fudge…. They might well have done x but they couldn’t have done y. x = an extreme terrestrial trait for which there is no evidence. So much for all that superiority posturing about Popperin flasifiability and requirinng “evidence”. y = a misrepresentation of an aquatic argument. -no-one is claiming we went through a marine stage.
The usual bullshit.
Oh, by the way, if you want to know which AAH proponents I’m thinking of, Marcel F. Williams is a prime example – relying on dedication to an idea rather than evidence in support of it E.g. https://paolov.wordpress.com/2013/04/28/the-aquatic-ape-hypothesis/#comment-16534
“Note here the pseudoskeptic fudge…. They might well have done x but they couldn’t have done y.”
Beautiful example of a strawman! Or should I say ‘pseudoscience fudge’ to match your tone?
I have NEVER said they “couldn’t have done y”. What I said was “it’s just as likely (if not more likely)” that they might have done x.
At was point does that become “couldn’t”? It doesn’t. It’s an equivocal statement with an indication that one of the conditions seems more plausible.
“no-one is claiming we went through a marine stage.
The usual bullshit.”
Williams makes the case for the structure of the human kidney being an adaptation for not having access to fresh water and being reliant on saline water. He links this with an aquatic phase in hominin evolution. That implies “marine”. It doesn’t imply pelagic, if that’s what you thought I was suggesting.
I notice that so far you haven’t actually presented any novel or useful information to this discussion, you’ve just been argumentative. I have provided several opportunities for you to contribute something meaningful (for instance asking for citations or links to your work), but you seem more intent on ranting about how much you dislike people who don’t agree with you. I’m afraid that ticks all the boxes of a time-waster and a troll.
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Please, I rely on the hard evidence.
The lobulated medullas in the human kidneys are a fact that you can’t hide from.
The fossil evidence that the bipedal Oreopithecus preferred a wetland environment is a fact that you can’t hide from.
But to add another interesting note to this discussion, there have been several scientist in the past who have argued that other fossil primates were once semiaquatically adapted. I’m referring to the subfossil giant prosimians of the island of Madagascar. Paleopropithecus, Archaeolemur, and Megaladapis have all been argued to have been semiaquatic in nature.
And I would also argue that the prosimian, Hadropithecus, probably waded bipedally in swamps for aquatic plants.
Some of these primates evolved some very strange features.
Marcel F. Williams
Camels also have the same structures in their kidneys. It’s an adaptation for reducing water loss in urine and it’s a convergent characteristic for mammals that have restricted access to fresh water. Such restricted access can be explained by a variety of different reasons – the observation from the kidneys would be just as good support for the human lineage adapting to an arid environment. Hardly conclusive and it limits any aquatic phase to a saline aquatic setting without ready access to fresh water – are you suggesting a fully marine aquatic phase in human evolution?
I know. I wrote a chapter on the evolution of the kidneys of camels in a book. Camels consume water and and eat plants from brine pools with salt contents– higher than that of seawater.
So are you advocating that humans evolved their kidneys from drinking salt water in the middle of the desert like camels do?
And baboons and geladas exist in extremely arid areas in Africa and in Saudi Arabia, yet their kidneys are like other catarrhine primates– unipyramidal.
Marcel F. Williams
They might well have done – it’s just as likely (if not more likely) than human ancestors going through an entirely marine stage. But I am not advancing any particular reason for human kidneys being the way they are, since that would be nothing more than speculation – which I will leave to you.
As to Baboons and Geladas, you do know that over most of their range they don’t have the issues with only being able to access highly saline water? So why as species would they be expected to develop these structures? They wouldn’t. Some populations might, but that would depend on the length of time that those populations were there for and utilising that water source – evolution doesn’t happen overnight.
We did not descend from aquatic apes, of course, although our ancestors were anatomically & physiologically not adapted to running over open plains as some anthropologists still believe. Instead, Pleistocene Homo populations simply followed the coasts & rivers in Africa & Eurasia (800 ka they even reached Flores >18 km overseas), google, eg, “econiche Homo”.
–eBook “Was Man more aquatic in the past?” introd.Phillip Tobias
–guest post at Greg Laden’s blog
Excuse me if I am getting out of bounds after so lengthy comments’ trends above, and/or if I am just not getting something, but as far as I could grasp, this hypothesis of the aquatic ape has as one of its basis the fact(oid?) of that only aquatic mammals and humans have significant subcutaneous fat; well, without thinking much or doing any research it jumps to my mind that also pigs and bears indeed do have subcutaneous fat. On the other hand, and most probably I am over-simplifying things, the increase and fixation of the human characteristic of having significant tendency to easily develop easily subcutaneous fat could be traced to the natural selection through the glacial periods on the humanoid and then human species and varieties that were around -on the other hand, I have to see that reversely it could be considered that the ‘aquatic period’ of ancestors apes could had come when the de-glaciation periods would cover enormous pieces of the land with water, converting them in gigantic more or less permanent marshes-. On the other hand the loss of body hair in humans could be considered an indication of an aquatic kind of life, but then this loss should be traced to a far away links in the apes-human evolutive chain, which up to what I can see hasn’t happened, and then again jumps to my mind that if there had been an aquatic ancestry in humans at ape level it seems logical that we wouldn’t/shouldn’t had lost the capacity to automatically and unconsciously close the back of the nasal airway as adults when getting submerged in the water -as well as an instinctive knowledge of swimming-, while babies keep it; this aptitudes seem to me to be as evolutively important if not more than the one of developing
heath-conserving subcutaneous fat if living in an aquatic ambiance. Lastly, our human skin does not seem to have evolved to resist long continual exposure to water, is enough to see how our fingertips’ skin get after a relatively quite short period of water immersion.
The proceedings of the symposium on waterside human evolution ‘Human Evolution: Past, Present & Future’ in London 8-10 May 2013 are published in 2 special editions of the journal Human Evolution:
Special Edition Part 1 (end 2013)
Introduction – Peter Rhys-Evans
1. Human’s Association with Water Bodies: the ‘Exaggerated Diving Reflex’ and its Relationship with the Evolutionary Allometry of Human Pelvic and Brain Sizes – Stephen Oppenheimer
2. Human Ecological Breadth: Why Neither Savanna nor Aquatic Hypotheses can Hold Water – JH Langdon
3. Endurance Running versus Underwater Foraging: an Anatomical and Palaeoecological Perspective – Stephen Munro
4. Wading Hypotheses of the Origin of Human Bipedalism – Algis Kuliukas
5. The Aquatic Ape Evolves: Common Misconceptions and Unproven Assumptions about the So-Called Aquatic Ape Hypothesis – Marc Verhaegen
6. The Epigenetic Emergence of Culture at the Coastline: Interaction of Genes, Nutrition, Environment and Demography – CL Broadhurst & Michael Crawford
Special Edition Part 2 (begin 2014) with 12 contributions.
The only problem with the so-called ‘aquatic ape theory’ is that the term is misleading for ill-informed people. More correct is e.g. ‘coastal dispersal model’: all archaic Homo sites have abundant edible shellfish (S.Munro 2010 “Molluscs as Ecological Indicators in Palaeoanthropological Contexts” PhD thesis Austr.Nat.Univ.Canberra). Rather than running over savannas (anatomically & physiologically impossible for our broadly built & heavy-boned & water+salt sweating Pleistocene ancestors), Pleistocene Homo simply followed the coasts & rivers (even in savannas sometimes :-D), collecting waterside & shallow aquatic plant & animal foods: in spite of fossilisation biases, Paleolithic coastal sites are found from Java & Flores (>18 km oversea) to the Cape & Angola (whale-butchering site Dungo V) to Pakefield & Boxgrove in England (M.Verhaegen 2013 “The aquatic ape evolves: common misconceptions and unproven assumptions about the so-called Aquatic Ape Hypothesis” Hum.Evol.28:237-266). Conventional approaches to human evolution typically only consider arboreal & terrestrial settings, but a biological approach shows that semi-aquatic habitats also were significant. Biological comparisons of extant & fossil hominoids with other animals lead to 3 hypotheses of ape & human evolution (instead of the traditional open plain running Man-the-Hunter ideas):
(1) aquarboreal Mio-Pliocene ‘apes’ & australopiths: According to paleo-environmental data, most Miocene hominoids lived in swamp, flooded or coastal (peri-Tethys) forests & wetlands (comparable to lowland gorillas today, e.g. google ‘gorilla bai’). They spent gradually more time in the swamp below the branches, collected floating aquatic herbs (AHV), hard-shelled foods (palm nuts, mangrove oysters, hard-shelled invertebrates HIS) etc., evolved vertical & below-branch climbing, a central & vertical & shorter lumbar spine, tail loss, a larger & wider body, stone tool use & thick enamel (partial durophagy).
(2) Pleistocene coastal dispersal of archaic Homo: Plio-Pleistocene Homo in forested & later more open coasts (continental shelves during glacials) spent more time in littoral waters, beach-combing, wading bipedally & diving for shell- & crayfish etc. They evolved shallow-diving skills, fur loss but fat layers, a projecting nose & midface, very heavy but brittle skeletons (for ballast cf pachyostotic littoral mammals), dorso-ventrally flattened femora (platymeria), skull-spine-legs in 1 line, flat-low-long skull-caps (platycephaly cf littoral mammals), larger brains (DHA), tool-making, oral adaptations for swallowing soft & slippery foods (closed tooth-row, small mouth, hyoidal descent, globular tongue, smooth & vaulted palate etc., preadaptative to pronouncing consonants in speech) etc.
(3) late-Pleistocene wading: Early H.sapiens spent more time wading for plant & animal foods from very shallow aquatic & waterside habitats. They evolved more gracile skeletons, very long (tibia) & straight legs, stronger basi-cranial flexion (to look down), pronounced chins & flatter faces, high-vaulted skulls, more complex tools & distance weapons etc.
If only there was the evidence to support the inference.
Paolo, there is plenty of evidence. Humans can learn to swim before they learn to walk. We swim better than chimps, we dive better than chimps. The one place a chimp is guaranteed to move (not just pose momentarily) bipedally is when they are in waist deep water. All of the peculiar phenotypic differences between us and our nearest ape cousins are easily explicable as the result of some (perhaps only slight) extra selection from wading, swimming and diving, and making a living in waterside niches. Can you name a single human traits that runs contrary to that assertion?
Algis, that isn’t evidence. It’s supposition based on observation. A counter observation would be that highly arboreal apes like Orangutans and Gibbons use bipedal locomotion when on the ground as a matter of course, since they lack secondary adaptations for knuckle-walking seen in Gorillas or (using a different mechanism) Chimpanzees. That may indicate that the Chimpanzee / Human common ancestor may have also been predominantly arboreal but bipedal on the ground and that Chimpanzee use of bipedalism in water is an artefact of an ancestral form of locomotion that is more suitable for wading.
When is “evidence” deemed “not evidence”? When it supports the crazy idea that human evolution might have been influenced slightly by wading, swimming or diving. When Dan Lieberman uses the same kind of argument (humans are better at ER than many mammals) everyone applauds.
Gibbons are highly specialised brachiators, their bipedalism is therefore highly derived. Orang-utans are largely quadramanous when on a patch of dry land but, of course, switch to bipedalism in waist deep water.
Wading is the perfect scenario to get otherwise quadrupedal apes to move bipedally. It cushions any energetic inefficiencies and compels them to move on two legs like no other scenario.
I ask you again: Can you point me to a single paper in the vast literature on bipedal origins that even discusses the idea, let alone rejects it? That’s not how science is supposed to work but gossip is fine when an idea can be exaggerated and lumped into the crazy box with creationism etc. (Thanks to people like Henry Gee)
It’s the simplest, most blatantly obvious idea on bipedal origins and anthropologist still just roll their eyes and sneer like ignorant teenagers. Incredible.
PaoloV, your writing about apes is totally irrelevant to the fact that archaic Homo dispersed along the coasts as far as the Paleolithic coastal sites of Mojokerto (barnacles), Flores (>18 km oversea), the Cape, Angola (whale butchering site Dungo V), Pakefield & Boxgrove, Gibraltar, Spain, S-France, Italy, Greece etc.etc. You seem to have a very outdated ideas on AAT, please see the proceedings of the conference “Human Evolution – past, present & future” on human waterside evolution (London 8-10 May 2013, with Don Johanson & David Attenborough), e.g. my contribution “The aquatic ape evolves: common misconceptions and unproven assumptions about the so-called Aquatic Ape Hypothesis” Hum Evol 28:237-266, 2013.
The evidence is overabundant: do you believe they ran over savannas from E.Africa to Mojokerto & Dmanisi & Aïn-Hanech? Only littoral animals disperse as far as that (e.g. pakicetids outside Pakistan). Mojokerto lay amid barnacles in deltaic sediments, Dmanisi was at the confluence of a big river not far from the Black-Caspian-Sea connection at the time. Archaic Homo had a lot of littoral adaptations: global dispersal, pachyostosis, ear exostoses, external nose, platycephaly, platymeria etc. Do you believe we got naked & fat to run over savannas, sweating water+salt? PaoloV, I suggest you inform properly, e.g. independent.academia.edu/marcverhaegen
Marc& Algis, the original aquatic ape hypothesis was not a littoral ape hypothesis – that is the result of changing hypotheses, which is fine, but don’t keep the old name when it is no longer descriptive. Large mammals are mobile and can disperse over large areas without being littoral (consider Leopards). Taphonomic factors favour preservation in aquatic habitats, so you would expect to find more materials in such environments. Many generalists utilise littoral environments, but are not strongly shaped by them as a species. The body fat observation is unfounded on closer inspection, so stop referencing it. I have yet to see a convincing argument to be made for the AAH that cannot be dismissed – it is no better at present than any other evolutionary just-so story, which other hypotheses are also guilty of.
PaoloV, who is interested in ‘original’ aq.ape hypotheses? We’re interested in what happened. Do you think there are leopards on Flores, the Cape & England? Global dispersal is typical of littoral mammals, e.g. pakicetids when they acquired pachy-osteo-sclerosis. And taphonomic factors don’t favour coastal fossilisation, on the contrary: most Pleistocene coasts are now some 100 m below sea-level. Nevertheless, AFAWK all archaic Homo fossils & tools lay amid large amounts of edible shellfish (some even marine), e.g. S.Munro 2010 “Molluscs as Ecological Indicators in Palaeoanthropological Contexts” PhD thesis Austr.Nat.Univ.Canberra. I’d think your problem is that you still believe in the old open-plain ideas, and have an outdated (‘original’) view on AAT. Homo’s coastal dispersal is beyond reasonable doubt, it’s no hypothesis, but a theory, confirmed by anatomical, physiological, fossil, archeological, paleo-environmental etc. data: they simply trekked along the coasts & from there inland along the rivers, e.g. M.Verhaegen 2013 “The aquatic ape evolves: common misconceptions and unproven assumptions about the so-called Aquatic Ape Hypothesis” Hum.Evol.28:237-266. AAT is not about apes or australopiths, not about what happened during the Miocene or even the Pliocene, but about Pleistocene Homo dispersing globally along the coasts.
Please don’t presume to tell me that my problem is belief in the open plains theory. I reject that as a ‘just so story’ as well, as I have explicitly stated elsewhere. This reliance on a false dichotomy demonstrates one of the reasons I have reservations about the quality of science involved in this area.
I have no real problem with the concept of coastal dispersal, although what I have a problem with is the assumption that coastal dispersal equates to requirements for adaptations to marine environments – it’s an unnecessary assumption that relies on uncritical observations. The subcutaneous body fat discussion is a prime example of an old observation that can be dismissed in light of subsequent observations, yet it still gets mentioned on a regular basis.
Moreover, evidence for utilising coastal resources is not evidence against other resources being used. Dispersal can be coastal even for a generalist species. You expect generalists to follow relatively easy to access continuous resources – raccoons, crows and rats are all obvious examples. We know that modern humans are generalists and it seems likely that our recent ancestors were as well, so citing a specialisation to a narrow habitat range for a relatively short period in an evolutionary lineage seems unnecessary, unless there is compelling evidence. You may find the evidence compelling, but I do not.
Yes, there are different steps in accepting AAT (in its modern form).
1) No serious scientist still believes the savanna hypothesis of Pleistocene Homo: it’s anatomically & physiologically impossible (e.g. sweat = water + salt, both scarce in savannas). This also includes the ideas that erectus-like people ran over open plains (for a demolition of this obsolete Man-the-Hunter fantasy, google “econiche Homo” table 4): endurance running is recent & restricted to a few E.African populations.
2) A paleolithic “coastal dispersal model” (S.Munro 2010 “Molluscs as Ecological Indicators in Palaeoanthropological Contexts” PhD thesis Austr.Nat.Univ.Canberra) is beyond serious doubt (as you now admit): how else can you go between Flores (>18 km oversea), Mojokerto (1.8 Ma + barnacles), the Cape, Dungo V (paleolithic whale butchering), Pakefield & Boxgrove (coastal sites in England)?
3) You still deny “adaptations to aquatic environments”, but soon you’ll have to admit this too. Humans are capable of diving for shellfish, so why wouldn’t human ancestors dispersing along coasts (see 2) not have dived for shellfish etc.? The facts are clear: there are at least 10 independent fossil indications (some stronger than other) that erectus-like people regularly dived for shallow sessile littoral foods: intercontinental dispersal (cf pakicetids), pachyosteosclerosis (typical of littoral animals), ear exostoses (as in human divers), platycephaly (e.g. seals), platymeria (id.), external nose (frequent in semi-aquatics), finds amid edible shellfish all over the Old World (S.Munro), very broad build (+ iliac flaring, long femoral necks & valgus knees, hindering running, but typical of shallow aquatics), drastic brain enlargement (typical of (semi)aquatics cf DHA), crossing to Flores (>18 km oversea), etc. IOW, there’s no doubt erectus-like people (probably during short period(s) see Mirceta cs 2013 Science) frequently dived for sessile littoral foods (shellfish etc.).
“The aquatic ape evolves: common misconceptions and unproven assumptions about the so-called Aquatic Ape Hypothesis” Hum.Evol.28:237-266, 2013 can be found at
I forgot to say: when H.erectus-like people arrived in E.Africa (Turkana c 1.8 Ma), it was together with stingrays, e.g. see the work of Feibel & Joordens: there was a marine connection at the time (probably with the Indian Ocean).
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