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Oh, no, not the Aquatic Ape Hypothesis again!

I think BAHFest — the festival of Bad Ad Hoc Hypotheses — has been made entirely redundant. It’s an event to mock the absurdly adaptationist hypotheses put forward by some scientists, and it’s intended to be extravagantly ridiculous. But then, you look at some ideas that are inexplicably popular among scientists, and you realize…it’s a little too close to reality.

I’m speaking of the Aquatic Ape Hypothesis.

The Guardian is running yet another article on the goofy idea that we evolved from swimming apes, and that all of the unique features of our species are a product of adaptations to an aquatic lifestyle. It’s complete nonsense: there is no evidence of long-term residence of our species in the water, and the proponents tend to invent the most outrageous panglossian explanations, fitting data to the hypotheses instead of the other way around. At least this story has one new contrivance I’d never heard before. Take it away, Rhys Evans!

“Humans have particularly large sinuses, spaces in the skull between our cheeks, noses and foreheads,” he added. “But why do we have empty spaces in our heads? It makes no sense until we consider the evolutionary perspective. Then it becomes clear: our sinuses acted as buoyancy aids that helped keep our heads above water.”

<stunned silence>

But…but…but every mammal, as far as I know, has a head full of sinuses! Have you ever taken a mouse skull apart? They’re amazingly spongy. Here are some sections through a mouse skull to show you what I mean:

mousesinuses-3
Coronal sections. There is a distinct osteomeatal complex within the nose that drains the true maxillary sinus as well as ethmoids. The true maxillary sinus is located lateral to the osteomeatal complex, and unlike the other sinuses, is lined by submucosal glands. This true maxillary sinus has a single ostium. Each nasal passage is separated by nasal septum. The posterior septum is deficient along its inferior aspect, and the two nasal passageways communicate freely just anterior to nasopharynx.

Isn’t that just beautiful? It’s fairly typical, too: mammals have these elaborate spaces to lighten the skull, humidify inspired air, and in some provide expanded surface area for olfaction — but I suspect the slight contribution of sinuses to those functions means that they’re actually a consequence of conserved developmental programs to build the skull. They’re there as a byproduct of developmental processes in which a scaffold is assembled first, and then thickens and fills in over time. The density of the skull is relatively easily regulated by modifying the timing of its development.

Just because they’re pretty, here’s another image of mouse skulls:

mousesinuses-4
Plates 1 and 2 display three-dimensional computed tomography (CT) reconstructions of mouse skull in axial and lateral-oblique views. Plates A to F display coronal fine cut CT scan images, confirming our histologic planes of section.

So, did mice have an aquatic ancestor? Doesn’t this hypothesis imply that every mammal descended from an aquatic ancestor? (I shouldn’t ask that: my experience with AAH fanatics is that they joyfully answer “yes” to the question.)

I also wonder if these people ever go swimming. Somehow, my sinuses don’t seem to work very effectively as water wings.

Michael Crawford offers a familiar absurdity: the nutritional argument from docosahexaenoic acid (DHA). DHA is one of those omega-3 fatty acids that is used to build brains, and it’s found in high concentration in lots of seafood. The true zealots consider this indisputable proof that we evolved by eating lots of clams.

“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.

“More to the point, we now face a world in which sources of DHA – our fish stocks – are threatened. That has crucial consequences for our species. Without plentiful DHA, we face a future of increased mental illness and intellectual deterioration. We need to face up to that urgently. That is the real lesson of the aquatic ape theory.”

An experiment: let’s feed zebras bucketloads of DHA, and watch their brains expand to 3-5 pound blobs that give them advanced communications abilities!

Oh, wait. It won’t work. There’s such a thing as neuroplasticity, but brains aren’t quite that flexible. I’m willing to believe that increased availability of the building blocks of brains might remove a constraint on growth, but not that it’s causal, as Crawford claims. Even feeding many generations of zebras DHA isn’t going to affect brain size much at all…and there’s no evidence that terrestrial herbivores are in any way limited by the availability of DHA.

For one thing, they synthesize it. We humans synthesize it, too. We also get it from the herbivores we eat, and certain plants are rich in the precursors to DHA. Vegans have to pay attention to get their DHA requirements met, but it’s not particularly difficult, and you don’t see lifelong vegetarians walking around with itty-bitty pinheads.

There are good reasons to be deeply concerned about declining fish stocks, but preserving a resource vital to the formation of our brains isn’t one of them. There are many people around the world who don’t eat seafood — there are entire ethnic groups who haven’t touched the stuff for generations. There are big-brained primate species that virtually never eat fish. How do they survive? How do they avoid “mental illness and intellectual deterioration”? They get it from other dietary sources.

Mammals in general are larger brained than other animals, are we to use that as an argument that all mammals went through an aquatic stage in their evolution…oh, wait. I did it again. The True Believers will just say “YES!” to that.

Comments

  1. Nick Gotts (formerly KG) says

    are we to use that as an argument that all mammals went through an aquatic stage in their evolution

    Sure they did: the period up to around 395 Mya.

  2. rowanvt says

    Only for certain definitions of ‘mammal’. After all, if they can redefine sinuses into floatation devices I’m sure they can redefine mammal in some equally bizarre way.

  3. Nerd of Redhead, Dances OM Trolls says

    The AA theory never made that much sense when first proposed, and it isn’t improved in the intervening years. The evidence is just too thin to even call it a hypothesis.

  4. morsgotha says

    Sinuses as floatation devices? What rot.

    Any scuba diver or swimmer who can swim pretty deep can tell you any air spaces in your skull are a hindrance to water living. Dive to 20 metres without equalising the air pressure and you will have intense pain in your ears.

    Dive much more than that without equalising and you will have perforated ear drums.

  5. Nick Gotts (formerly KG) says

    When I was a child (7 or 8, I think), I used to browse the local public library. One time, I happened on a book called The Sea Ape, which had a colour plate of the eponymous creature emerging from its watery abode which very nearly scared the shit out of me the first time I saw it – I can’t find the image itself online, but if memory serves it looked more like a zombie than an actual ape. However, on subsequent visits, I could seldom resist opening the book again for another look. Could this have been an ancestral memory of a time when atavistic aquatic anthropoids emerged from the sea to snatch the children of their more evolved relatives?

    A: No, but I recommend the book to AAH proponents who want better evidence than they have presented thus far.

  6. Nick Gotts (formerly KG) says

    PZ@2,

    Yeah, I know, but it was still a stage in their evolution. It was a jest.

  7. Sili says

    Even Dunnning managed to get this one right.

    Of course all mammals have gone through an aquatic stage. Dry wombs only work in marsupials.

  8. The Mellow Monkey says

    I love the AAH. Why? Because when I was a kid, I stumbled upon a book in the library which was written from a feminist perspective and completely and wholeheartedly embraced the AAH…as the stepping stone toward patriarchy. (This might have been an Elaine Morgan book, though if it was I have no idea which one.) It was stuff like “the water made the female buttocks and thighs grow so large that the male’s tiny primate penis could no longer reach from behind and so face-to-face coupling was invented, but this is not some tender and emotional and humane act! Oh no! This began as rape when the male became angry about his tiny penis and threw a female down on her back.”

    I was probably about eleven at the time, so this was seriously O_O stuff. I started reading books on human evolution and feminism and rapidly discovered that all sorts of hypotheses virulently disagreed with one another. There was no gospel truth, only ideas and best guesses and “this is statistically likely” and figuring out what the evidence supported. And people who had been working in the same field their entire adult lives and looking at the same evidence could still disagree, but when almost everyone agreed about something and the evidence supported it, then it moved into the “most likely true” category. Yet, still, new evidence could always change that. This was what made it science.

    I credit the AAH for sparking my skepticism.

  9. ChasCPeterson says

    please don’t use quotation marks when you’re just making shit up paraphrasing from memory.

    Then it becomes clear: our sinuses acted as buoyancy aids that helped keep our heads above water.

    I literally LOLed.

    humidify inspired air

    Not only humidify, but also warm. This system can be tweaked to conserve water and heat. As cool, dry air is inhaled past the turbinates (

    Dry wombs only work in marsupials.

  10. multicellular says

    The $64 question is how big would the sinuses actually need to be to float the average human head?

  11. Chuck says

    I thought we lost hair because of neoteny, but here I come to find we were all aquatic apes once.

  12. ChasCPeterson says

    oops…here’s the rest:

    …turbinates (those scroll-shaped bones in the mouse-skull pics, cpvered in life with living epithelium), it is humidified and warmed, but in the process the turbinate surface is cooled (by convection and evaporation). Upon exhaling, now warm and saturated air passes the relatively cooler turbinates and some of the water (in some cases–kangaroo rates, e.g.–almost all of it) condenses out and is reclaimed, along with the heat of condensation.
    In fact, fossil evidence of nasal turbinates is used to infer the endothermy of mammalian ancestors, so these spaces are important.

    Dry wombs only work in marsupials.

    wut.
    Marsupials have a perfectly good (if relatively short-lived) amnion full of fluid just like every other amniote. (And, contrary to popular belief, a placenta too.)

    In fact, all vertebrates are still constrained to develop underwater. Terrestrial arthropods have our butts kicked in that department.

    But none of this has anything to do with the stoopid AAH.

  13. ChasCPeterson says

    I thought we lost hair because of neoteny, but here I come to find we were all aquatic apes once.

    not mutually exclusive. Proximate vs. ultimate explanations.

  14. Pierce R. Butler says

    Wouldn’t a shallow-water habitat produce conditions likely to preserve a whole lot of fossils?

    If Neil Shubin & Co could spend months and months camping on bare-rock islands in the Arctic to find Tiktaalik, why don’t the AAHists treat themselves to a nice tropical Indian Ocean coastal vacation and come back with a nice set of super-sinused skulls to confound our esteemed host and his fellow strident critics?

  15. mildlymagnificent says

    My heart sank when I saw that Guardian piece. Why don’t these people spare a moment’s consideration for those of us who toil in the moderation quagmire of science forums where daft ideas get circulated again and again and again and….. Just this week as I gazed open-mouthed at yet another attempted “refutation” of well-founded science (Einstein this time) I consoled myself that at least no one was hawking that infernal aquatic ape nonsense recently.

    I dread to think what will be lurking for my next log in.

  16. Sharon C says

    Any scuba diver or swimmer who can swim pretty deep can tell you any air spaces in your skull are a hindrance to water living. Dive to 20 metres without equalising the air pressure and you will have intense pain in your ears.

    Dive much more than that without equalising and you will have perforated ear drums.

    Seconded! Not only that, but add in any kind of head cold, and you’re likely to have sinus block (going down), or sinus squeeze (coming up), and be blowing blood in your mask.

  17. carlie says

    Go search for #spaceape on Twitter. Everyone is sharing characteristics of humans that make it obvious that we evolved in space instead. :)

    You have to love the erratum at the end of the article:

    “This article was amended on Saturday 27 April to add a “no” to this quote: “we would have to have spent millions of years there and there is evidence for this”.”

  18. The Mellow Monkey says

    Chas

    please don’t use quotation marks when you’re just making shit upparaphrasing from memory.

    Okay. It was Elaine Morgan after all. From The Descent of Woman:

    The primate was a totally different shape. Her new aquatic streamlining had been unable to prevent her becoming lumpy in the middle, and as a littoral biped her legs were developing in the opposite direction from the seal’s – they were becoming not smaller and thinner but farther apart, but longer and thicker and closer together. The seal’s solution was impossible for the aquatic apes. Their dilemma was unique.

    So we left her on her back, kicking and struggling and frightened out of her tiny anthropoid mind, with her mate beginning to get irritated. When she saw him snarl and bare his canines she was finally convinced that he wanted her for dinner, and that her last hour had come. Further resistance was useless. She stopped fighting and signaled her submission, defeat, and appeasement as strongly as she could with so little room for maneuver.

    And:

    Meanwhile, for the first time in the history of life, the sex act had been accomplished by force in an atmosphere of hostility and fear and violence. The first tenuous mental connections had begun to be laid down between sex and ruthlessness on one side, and sex and suffering on the other. We had taken the first step along the tortuous road that led to the sex war, to sadomasochism, and ultimately to the whole contemporary snarl-up, to prostitution, prudery, Casanova, John Knox, Marie Stopes, white slavery, women’s liberation, Playboy magazine, crimes passionels, censorship, strip clubs, alimony, pornography, and a dozen different brands of mania.

    This was the fall of man, it had nothing to do with apples.

    These are from an older edition of the book. She still makes the same connections in the newest edition, but Chapter Four “Aggression” has been replaced with “Orgasm” and focuses more on sexual satisfaction than rape as a result of thick thighs.

  19. stevem says

    re morsgotha@5:

    Any scuba diver or swimmer who can swim pretty deep can tell you any air spaces in your skull are a hindrance to water living. Dive to 20 metres without equalising the air pressure and you will have intense pain in your ears.

    Dive much more than that without equalising and you will have perforated ear drums.

    There’s your proof, right there! Sinuses are flotation devices, not for diving at all. After all, if you’re an aquatic species, why would you ever want to dive anyway? To catch fish? Absurd. Water is just to float in and stay cool during those hot African summers, doncha know.

    But seriously, I first read the aquatic ape hypothesis as a real feminist rebuttal to the whole “naked ape” trope by Desmond Morris. While cherry-picking different features of our physiology and relating them to possible aquatic influence, it really highlighted the patriarchal influence on current thinking of human evolution. [such as breast size; Morris says breasts are big to look like butts(because males are 'turned on' by butts), AAH says they are big to float in the water so baby can find them easier.(survival trumps sexy)] But even so, it played its part but is now obsolete, so science must now march on.

  20. Pteryxx says

    The primate was a totally different shape. Her new aquatic streamlining had been unable to prevent her becoming lumpy in the middle, and as a littoral biped her legs were developing in the opposite direction from the seal’s – they were becoming not smaller and thinner but farther apart, but longer and thicker and closer together. The seal’s solution was impossible for the aquatic apes. Their dilemma was unique.

    …I’ll just leave this here…

    Backside of female Celebus crested macaque (via Cracked

  21. stevem says

    re 20:

    Oh yes, The Descent of Woman is what I first read of the AAH, but isn’t her name actually Mrgan, not Morgan? Just asking, maybe the edition I had was a misprint. IDK.

  22. joedo says

    Sinuses also produce NO and without it lung function is abnormal (in humans at least) so they do more than simple warming & humidification. Also dolphins have adapted to the aquatic environment by developing unihemispheric sleep. When one hemisphere is asleep they don’t lose depth perception, ability to avoid obstacles or catch prey. I think a better explanation for increased brain size could be the extra capacity required to function normally on one hemisphere.

  23. stevem says

    re 24:

    I think a better explanation for increased brain size could be the extra capacity required to function normally on one hemisphere.

    Not to mention interpreting those “echoes” as images and not just ‘pings’, must take a lot of processing power.

  24. The Mellow Monkey says

    stevem, it’s Morgan everywhere I’ve seen. I think her books–especially the ones that came out in the ’70s–were really important for offering that counter-argument to the male-dominated narrative, like you said. Even though later I dismissed most of what I read in that book, it was good to remember women were part of the evolutionary landscape as well and not just being shaped by male desires.

  25. ChasCPeterson says

    Thanks for the direct quotes:

    So we left her on her back, kicking and struggling and frightened out of her tiny anthropoid mind, with her mate beginning to get irritated. When she saw him snarl and bare his canines she was finally convinced that he wanted her for dinner, and that her last hour had come. Further resistance was useless. She stopped fighting and signaled her submission, defeat, and appeasement as strongly as she could with so little room for maneuver.

    wow, that’s…that’s just so thoroughly stupid from top to bottom. I’m speechless.
    (By the way, did you know that horned lizards also mate (at least sometimes) front-to-front? ‘strue.)

    survival trumps sexy

    Except that’s empirically false. Trivial example: peacocks. Key words for further info: ‘honest advertisement’ and ‘handicap principle’.

    And…wut? Human breasts were designed to float independently of a woman’s torso? That idea is refuted by…well, by pretty much every pair I’ve ever had the opportunity to investigate.

  26. says

    A friend pointed out to me today that the context in which Elaine Morgan wrote The Aquatic Ape was heaving with fairly ropey monocausal explanations for human physiology in terms of what males were doing, from the likes of Owen Lovejoy and co – females sitting around in base camps while the males were off on the savannah, chucking rocks at wildebeests and being generally evolutionarily dynamic. I suppose I feel slightly more forgiving of such ropey science given the context in which she was operating. However, we have no evidence whatsoever for the exploitation of aquatic resources prior to 1.95 mya, which somewhat undermines the entire edifice.

  27. anthrosciguy says

    As PZ knows, my website on the AAT/H has a lot of info on it. On several pages I mention the serious misunderstandings (and/or misuse) of evolutionary theory on the part of Michael Crawford and the DHA/brain argument wing of the AAT/H.

    One such is the comparison he makes with zebras versus bottlenose dolphins. There are general trends concerning brain size, and one strong correlation is predators versus prey. Predators, especially social predators such as dolphins, tend to have much larger brain to body size ratio than herbivores. So making that comparison doesn’t make sense, and can only be done by someone who is unaware of basic evolutionary theory surrounding brain size, or who is being deliberately dishonest. Either one means that Crawford’s claims cannot be trusted.

    There’s also the fact that human brains can and have grown normally in populations without access to aquatic foods. That shoots a big hole in the aquatic diet claim too; in fact it destroys it. It also demonstrates that the people making the claim don’t understand evolutionary theory.

    The page on my site about the DHA argument is called The Omega-3 Gang, and there’s more information on my page about David Attenborough’s BBC Radio show on the AAT/H a few years back (Attenborough is a true believer too). Links at the bottom of this comment.
    This is all coming up as part of a PR push for an upcoming conference the AAT/H crowd has put together for May 8th and 9th. Besides the usual AAT/H proponents, including Attenborough, they’ve got Donald Johanson coming. I look forward to seeing how they use whatever he might say to claim support, as they have with other statements from various academics in the past.

    The Omega-3 Gang

    BBC Radio show

  28. Amphiox says

    And here I had always thought that the sinuses and nasal turbinates were relatively small in humans compared to other animals.

  29. David Marjanović says

    Tetrapod Zoology has had a few articles about that. I highly recommend them.

    But…but…but every mammal, as far as I know, has a head full of sinuses!

    It even goes beyond mammals a bit.

    Marsupials have a perfectly good (if relatively short-lived) amnion full of fluid just like every other amniote. (And, contrary to popular belief, a placenta too.)

    Bandicoots have a placenta. Are you sure about the others?

    Wouldn’t a shallow-water habitat produce conditions likely to preserve a whole lot of fossils?

    Well… yes. :-)

    You have to love the erratum at the end of the article:

    X-D

    but isn’t her name actually Mrgan, not Morgan? Just asking, maybe the edition I had was a misprint. IDK.

    o_O That’s a rather bizarre misprint, yes!

    I think a better explanation for increased brain size could be the extra capacity required to function normally on one hemisphere.

    Then what about elephants? And elephant-nose fish?

    (By the way, did you know that horned lizards also mate (at least sometimes) front-to-front? ‘strue.)

    Also, bonobos do it often, chimps rarely or never (I forgot).

    the context in which Elaine Morgan wrote The Aquatic Ape was heaving with fairly ropey monocausal explanations for human physiology in terms of what males were doing

    Yep, those were the times of “Man the Hunter”.

  30. anthrosciguy says

    (By the way, did you know that horned lizards also mate (at least sometimes) front-to-front? ‘strue.)

    Also, bonobos do it often, chimps rarely or never (I forgot).

    From my site:

    Also seen in orangs, black-handed spider monkeys, and occasionally in woolly spider monkeys and gorillas; and only some very specialized aquatic mammals which have been aquatic for several tens of millions of years.

    Basically, among aquatic mammals it’s only done by those which are incapable of doing so any other way due to their bodies’ adaptations. This is obviously not true of humans.

  31. stevem says

    re 26:

    stevem, it’s Morgan everywhere I’ve seen.

    OOPS! I guess I must have been think of Sarah Hrdy (often written Hardy), also associated with the “female-driven-evolution” trope. Sorry for the confusion. [hmmm, Where did I leave that book anyway...]

  32. ChasCPeterson says

    Attenborough is a true believer

    That’s…disappointing.

    Bandicoots have a placenta. Are you sure about the others?

    (without looking it up)(yet): Pretty sure. As I recall, it’s choriovitelline instead of the eutherian chorioallantoic style, but they must have one. The only alternative would seem to be a full-on yolk sac, and I’m sure I’ve never seen reference to that.

  33. Amphiox says

    I stumbled onto Morgan’s books (Descent of Woman and Aquatic Ape) when I was a teenager. Those books were what got me first interested in both human origins/evolution and feminism. I think I was a true believer for about 2-3 years in high school. I recall initially wanting to do by IB science project on the subject before being talked out of it. My father, who knew more about how science worked than I did at the time, advised me that a project that was just a glorified book report would not score highly, and that a science projected needed an experiment to be conducted, and I realized that it wasn’t possible to design an experiment that could test the AAH.

    Going through that process was how I finally understood what “just-so” story meant and why it was something to be avoided like the plague when thinking about evolution.

  34. katie says

    But why do we have empty spaces in our heads?

    The jokes just write themselves sometimes, don’t they?

  35. Azkyroth Drinked the Grammar Too :) says

    please don’t use quotation marks when you’re just making shit up paraphrasing from memory.

    That was uncalled for.

  36. evilDoug says

    Then it becomes clear: our sinuses acted as buoyancy aids that helped keep our heads above water

    “Location, location, location” ain’t just applicable to real estate. ‘umans an’ ‘ominids ‘ave their ‘ead ‘oles (at least the ones for breathing) on the front – and not well out front like amphibious mammals, but rather smooshed in.
    For anything to contribute to buoyancy in water, it has to be at least partially immersed in said water. Sinuses in the front of the face might help a bit in keeping the nose out of water in a supine posture, which I guess might be useful while sleeping, admittedly a good thing, but not for much of anything else. The total volume of modern human sinuses, as far as I can find without actually working at it, is around 30 millilitres, which at best would contribute buoyancy amounting to less than 1% of the mass of a modern human head. Even if you scooped out the brain and replaced it with aerogel, the overall effect on whole-body buoyancy would not be all that great. Some extra lung capacity would do more for buoyancy, not to mention survival time between breaths. A big blubbery neck would make a useful head floatation device.

  37. dustbunny says

    “our sinuses acted as buoyancy aids that helped keep our heads above water.”

    *blink*

    I have had a very lousy, frustrating day and probably haven’t even smiled at all, but that sentence right there just made me laugh out loud. That is so extraordinarily ridiculous I can’t believe someone argued for that in earnest.

  38. says

    The lack of fossil evidence argument against AAH strikes me as being a bit thin. After all, we’re talking about a group of mammals that haven’t until recently been very populous, and what fossils there were would likely be in drowned locations. In the standard narrative, are we even sure at what point of evolution we went from furry to nearly naked, or when we developed long head hair?

    I’ll admit to a little bias: I read Morgan’s Descent of Woman in my impressionable teens. I accept now that it’s a just-so story, but it’s an appealing one.

  39. thumper1990 says

    I’ve never come across this theory before; it’s fascinatingly ridiculous. I’m trying hard to think of any bodily adaptions in humans which could, on the face of it, be interpreted as purely aquatic… and the only one I can think of is the webbing between our fingers and toes. Perhaps someone better educated in these matters than I can help; is there an evolutionary explanation for the fact humans have partially webbed digits? Or is it just… there?

  40. thumper1990 says

    Thanks John :) That was interesting. From what I can tell, there are no major proponents of this theory that have any relavent qualifications; and judging from this Morgan person’s intentionally misleading references, cherry-picking of quotes and, at least when it comes to seals and their sweat glands, downright lies, I would say she knows full well the theory is bollocks.

    Good to know :)

  41. ChasCPeterson says

    is there an evolutionary explanation for the fact humans have partially webbed digits?

    *checks feet, hands*

    “fact”, you say?

  42. Antiochus Epiphanes says

    After all, we’re talking about a group of mammals that haven’t until recently been very populous, and what fossils there were would likely be in drowned locations.

    Like whales, amirite?

  43. David Marjanović says

    what fossils there were would likely be in drowned locations

    Only if our semiaquatic ancestors stayed well clear of freshwater, and only if the semiaquatic phase was entirely restricted to one glacial. The sea goes, and the sea comes – just last interglacial the sea level was 10 m higher than today.

    In the standard narrative, are we even sure at what point of evolution we went from furry to nearly naked, or when we developed long head hair?

    No; but shorter hair makes sense as an adaptation to shed heat on the savanna, except on the head that needs to be protected from the sun, so the prediction is that all this started when our ancestors got out of the forest (or the closed forest retreated from above their heads) something like 2 million years ago. Also, see this on hair.

    As I recall, it’s choriovitelline instead of the eutherian chorioallantoic style

    …Oh. That makes sense. The placenta of bandicoots is indeed chorioallantoic, and I’m sure that lack of involvement of the allantois used to be handwaved away as “doesn’t count”.

    BTW, the yolk sac does occasionally (individual variation) participate in forming the placenta in placentals, IIRC including humans.

    the webbing between our fingers and toes

    You call that “webbing”?

  44. Amphiox says

    If I recall, someone used the genetic divergence of human pubic lice (which are a district species from head lice) to estimate a date for when humans “lost” their body hair. I can’t recall the number they came up with.

  45. The Mellow Monkey says

    In the standard narrative, are we even sure at what point of evolution we went from furry to nearly naked, or when we developed long head hair?
    There are some good ideas. Genetic analysis points to the current common African version of the MC1R gene (which specifies a protein that controls for two kinds of pigment in humans) sweeping the population 1.2 million years ago, while outside of Africa and within chimpanzees this gene has a lot of variations. This would point to dark skin being advantageous at some point before then. Dr. David Reed’s research into the genetics of human pubic lice has them diverging from the gorilla louse 3.3 million years ago.

    The NYT article throws in some just-so stories about sex selection and women being sexier without hair, but the actual research is what’s important here, not narratives: Even if we lack fossils showing the loss of long, thick body hair, we can still look at genes and see that our skin has most likely been exposed to the sun for over a million years. Possibly longer, if it goes back as far as the great louse divide.

  46. says

    Antiochus Epiphanes, how many fossil specimens are we talking about in the whales’ case? My recollection may be faulty, but I was under the impression that the definitive transitional forms were discovered only relatively recently. Certainly there are few enough Homo specimens discovered so far that we shouldn’t be confident that there are no surprises yet to be found in our history. H. floresiensis comes to mind (though a distant cousin rather than an ancestor).

  47. says

    The human louse (or lice) is a good example of the kind of indirect evidence we can point to, rather than explicit fossils which inevitably are going to be rare. Do otters and seals have lice? Are their lice adapted to aquatic or amphibious lifestyle? Perhaps the mere existence of an unbroken lice line going back to 3 million years ago is evidence against AAH, but I don’t know anything about lice lifestyles.

  48. Antiochus Epiphanes says

    NelC: Someone with more knowledge than me should probably weigh in (or you could query The Paleobiology Database), but I’m under the impression that both the human fossil record and the whale fossil record are pretty rich*. The database shows that some of the transitional forms were on record as early as the 1950’s, but making sense of them didn’t take place until (I think) the late 1980’s and earl 1990’s.

    True, someone might find fossil evidence of a littoral hominin, but until they do, the aquatic ape hypothesis isn’t required to explain anything. Since it assumes more than the standard hypothesis, and explains less, it isn’t to be preferred.

    *Or exhibit collector bias. Which would mean that we have more fossils in hand than one would expect given some mean rate of recovery for like organisms. I work in an entire order with a fossil record consisting only of pollen, so it seems pretty rich to me.

  49. The Mellow Monkey says

    Otters don’t have any known fur parasites. There is such a thing as a seal louse. Human louse species don’t have the same adaptations to water that the seal louse has.

    Incidentally, widespread and uniform dark pigmentation can be a very unfavorable coloring in aquatic animals, especially if the animal is as slow as a human is in water. A dark back and pale underbelly is more common, because this helps the animal blend in with the sky when seen from below. Dark-skinned hominins would have been unfortunately visible to predators while swimming. Staying lighter skinned like chimpanzees would be more beneficial in that environment. However, being out in the sun all day on dry land? That’s a great place for sun protection.

  50. joedo says

    Re: lice comment. I think head & body lice are closely related and appearance of body lice was used to date when humans started wearing clothes those being essential to survive in sparse or no hair. If memory serves, I believe pubic lice are more genetically similar to gorilla lice, which opens a whole other bag of worms about our ancestor’s indiscretions.

  51. says

    Antiochus Epiphanes, according to that database there are only 41 specimens of H. erectus — the most numerous human ancestor fossils, it looks like — which for a professional in the field is probably a rich selection. But in absolute numbers it’s not a huge amount; I stand by my characterisation as “rare”. With those kinds of numbers recovered from locations favouring preservation and recovery, I don’t believe that one could reasonably expect to have recovered fossils from locations that don’t.

    Mellow Monkey, those are indeed stronger arguments against AAH than lack of fossils, IMO.

  52. ChasCPeterson says

    Incidentally, widespread and uniform dark pigmentation can be a very unfavorable coloring in aquatic animals, especially if the animal is as slow as a human is in water. A dark back and pale underbelly is more common, because this helps the animal blend in with the sky when seen from below. Dark-skinned hominins would have been unfortunately visible to predators while swimming. Staying lighter skinned like chimpanzees would be more beneficial in that environment.

    Not buying it. Aquatic mammals are not generally countershaded (some dolphins excepted), and countershading isn’t much help for something at the surface anyway. I doubt even the most ardent AAH proponent thinks our ancestors spent much time cruising the mid-water-column.
    Plus, what predators are you talking about? Big sharks…period. Crocodiles don’t hunt from below. And the chief prey of big sharks today–pinnipeds–are not necessarily countershaded.

    In general, it’s a poor idea to argue against a just-so story with one of your own.

  53. marc verhaegen says

    Discussions on the so-called “aquatic ape theory” are often irrelevant & outdated, not considering the recent literature on the subject.
    Humans didn’t descend from aquatic apes, of course, although our Pleistocene ancestors were too slow & heavy for regular running over open plains as some anthropologists still believe.
    Instead, Homo populations during the Ice Ages (with sea-levels often 100 m lower than today) simply followed the coasts & rivers in Africa & Eurasia, eg, 800,000 years ago, they even reached Flores more than 18 km overseas.
    Some recent info:
    – google “econiche Homo”
    – eBook Was Man more aquatic in the past? introduction Phillip Tobias http://www.benthamscience.com/ebooks/9781608052448/index.htm
    – guest post at Greg Laden’s blog http://scienceblogs.com/gregladen/2013/01/30/common-misconceptions-and-unproven-assumptions-about-the-aquatic-ape-theory
    http://greencomet.org/2013/05/26/aquatic-ape-the-theory-evolves/
    – Human Evolution conference London 8–10 May 2013 with David Attenborough, Don Johanson etc. http://www.royalmarsden.nhs.uk/education/education-conference-centre/study-days-conferences/pages/2013-evolution.aspx
    – M Verhaegen & S Munro 2011 “Pachyosteosclerosis suggests archaic Homo frequently collected sessile littoral foods” HOMO – J compar hum Biol 62:237-247
    – M Vaneechoutte, S Munro & M Verhaegen 2012 “Reply to John Langdon’s review of the eBook: Was Man more aquatic in the past?” HOMO – J compar hum Biol 63:496-503
    – for ape & australopith evolution google “aquarboreal”
    marc verhaegen tech.groups.yahoo.com/group/AAT