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The Evolution of Bipedalism and the Aquatic Ape Theory by Biskie

Posted by: | March 13, 2008 | 24 Comments |

Bipedalism is a rare characteristic in the animal kingdom and humans are the only mammals to walk and run on two legs habitually. There must have been very strong selection pressures for it to have evolved. Many theories have been put forward to try to explain how this might have come about.
Darwin was one of the first commentators on human bipedalism in 1871. He believed that the freeing of the hands for tool use could be the explanation. However, this theory has been discredited by the discovery that bipedalism predates the earliest found tools by about one million years. Bipedalism also predates the significant increase in brain size that was most likely needed for the manufacture of tools. The regular use of stone tools and the increase in brain capacity are believed to first appear with the species Homo Habilis 2.4 million years ago.
Bipedalism in the human lineage has been dated to roughly four million years ago. This antiquity was not widely appreciated until the 1960s. The discovery of the “Lucy” skeleton in 1974 helped to dispel any remaining doubts. Although Lucy does not show all the adaptations to bipedalism that modern humans do, such as the lockable knee, it is accepted that she could and did walk bipedally. She belongs to the species Australopithicus afarensis and her skeleton is dated at 3.2 million years ago. Further evidence for early bipedalism comes from the track of hominid footprints found at Laetoli, thought to have been made by a member of the species A. afarensis about 3.7 million years ago.
Fifer (1987) proposed that bipedalism arose so that our ancestors could be good stone throwers so as to ward off predators. Kortland’s similar theory (1980) is that it evolved from the use of forelimbs to brandish thornbush branches to ward off attack by carnivores. Both of these theories overlook the obvious disadvantages of standing upright in these situations: namely that bipeds are easier to knock over, are more conspicious and less agile when dodging, feinting and other escape tactics.
Hewes (1961,1964) and Lovejoy (1981) believed that advantages of being able to carry meat and other food items back to a home base was the driving evolutionary force behind bipedalism. Hewes thought that only by the freeing of the arms and hands could “maximal transportational efficiency” be achieved. Meat would need to be carried and would require picking, gnawing and chewing slowly. This would be much safer to do at a home base than out on the savannah.
Meat eating and hunting proper are now generally considered to have become established far later in our evolution, about the time of Homo habilis. Lovejoy therefore proposes that vegetable foodstuffs would be collected and brought back to the camp. There would be division of labour with the females staying at home to care for offspring. Lovejoy proposes that this happened in a forest environment before the move onto the savannah. This scenario assumes that pair-bonding was established, however there are no documented examples of this type of behaviour among non-human primates. The gibbon is the only known pair-bonded primate and the males have not been observed offering food to the females. Primates are also far more likey to run on three legs when carrying objects. We need to consider if this version of events would lead to males being far more efficient at bipedal locomotion than females.
Rodman and McHenry (1980) suggest that bipedalism arose because at normal walking speeds it is more efficient than quadrepedalism. This was enlarged on by Shipman (1984) who believed that this was an adaptation to a meat-scavenging life-style where long distances would be travelled at relatively slow speeds. However, many other animals need to travel long distances at slow speeds eg when searching for food and water or when migrating and they all do so on four legs. If a higher level of efficiency is required then it is far more likely that refinements and improvements will occur on the original system rather than a wholly new one emerging. A considerable rearrangement is necessary in the structure of the body for a quadruped to become an adept biped.
Another savannah theory has a thermoregulatory basis. This idea proposes that a bipedal hominid has an advantge over a quadrupedal one in that it will receive less radiation from the sun when it is in an overhead position. This “sunshine theory” was first touched on by R W Newman in 1970 and later elaborated on by Pete Wheeler (1984). In the midday sun a bipedal hominid would present 40% of the area that a quaduped would expose to the sun’s rays. It is an intricate theory linked to loss of body hair and involving considerations such as water and energy budgets. Critics argue that alternative effective methods of dealing with overheating are more likely to have evolved, ones which did not require such extensive skeletal rearrangements. Also, no other savannah animal, living under the same conditions, has gone down the same evolutionary path as we have.
Many who study human evolution believe that none of the “savannah theories” provide sufficiently strong selection pressures to outweigh the many disadvantages of bipedalism in the savannah environment. As well as all the muscular remodelling that was necessary, the change to bipedalism altered the angle of the birth canal in females resulting in a more difficult mode of giving birth. Even now, possibly 4 million years later, we are paying the price. More days are taken off work due to back pain than to any other complaint. Our hearts work harder to pump blood around our bodies due to the enhanced gravitational pull on blood returning from the legs. The extra strain on our hearts may cause high blood pressure and we may suffer from varicose veins due to valves failing in over-worked veins (Morgan, 1990). These are sometimes referred to as our “scars of evolution”. Because we are not currently perfectly adapted to our present environment we should perhaps question whether we were at one point in our evolution better adapted to a wholly different environment.
In 1960 Professor Sir Alister Hardy proposed that we must have had an aquatic phase in our evolution. He suggests that at an early stage of hominid evolution, early in the fossil gap, the area of land inhabited by a group of hominids became flooded. Morgan later suggested that this area was the Afar triangle/Danakil desert, which is a low lying area known to have been flooded at this time. This flooding would have lead to an environment of flooded forests, islands and mangrove swamps. Hominids living here would have spent a lot of time in the water, probably coming to rely on it for the abundant and nutritious food sources it contained.
When wading in water there are obvious advantages to being bipedal, the major one being that one can walk further in without drowning. A bipedal posture also presents less resistance when walking through water and means that one can look down to the ground for food without needing to be completely submerged.
Swimming is far easier with a steamlined bipedal shape. There would be strong selection pressure for legs in line with the body. There are many compelling feautres of a study of comparative anatomy that support the aquatic ape theory.
Characteristics Humans Apes Savannah Aquatics
bipedalism yes
loss of body hair yes yes yes
subcutaneous fat yes yes
ventro-ventral
copulation yes yes yes
loss of apocrine
glands yes yes
hymen yes yes
sebaceous glands yes yes
tears yes yes
loss of vibrissae yes yes
(whiskers)
breath control yes yes
eccrine thermoreg. yes yes
descended larynx yes yes
(Elaine Morgan)
There is some evidence from the behaviour of the probocis monkey that water tends to promote bipedalism. They live in the mangrove swamps of Borneo, are good swimmers and walk into water on two legs. They have even been observed walking bipedally when on land.
For further reading see:
Morgan, E (1984) “The aquatic hypothesis”, New Scientist, 12th April, 11-13
Morgan, E (1990) “The Scars of Evolution: What our bodies tell us about human origins”. London, Souvenir Press

under: Philosophy of science

24 Comments

  1. By: boltonian on March 13, 2008 at 7:04 pm      

    Biskie:

    Good stuff. I am, as you know, a fan of the Aquatic Ape hypothesis.

    I must get hold of ‘The Scars of Evolution.’

    PS – is there a reason why we have the article twice?

  2. By: Biskie on March 13, 2008 at 8:05 pm      

    Hi, there is supposed to be a table near the end but it’s got all squished up (I did wonder if that might happen as I didn’t do it with proper columns). Can you sort it out Gordy?

  3. By: gordy on March 14, 2008 at 8:47 am      

    The reason why we had it twice and the table thing are linked in a way -I was trying to sort out the formatting. We now only have it once but the table thing is proving tricky…

  4. By: gordy on March 14, 2008 at 9:18 am      

    Biskie
    If you were able to put the table thing in Word format and email it to me I’d be able to include it as a separate file attached to the article.

  5. By: Biskie on March 14, 2008 at 9:56 am      

    Oh if only it were that simple Gordy. Even though I have an all singing all dancing pc I don’t have Word on it because I STILL haven’t got round to buying Office 2000 or whatever it is that I probably need. Perhaps this is the kick up the arse I need. I feel a price comparison search coming on.

  6. By: anthrosciguy on March 21, 2008 at 8:31 pm      

    I’ve got a nicely formatted table of that characteristics list on my site. I also have an annotated version which corrects the errors (every entry on the list is actually in error). It’s part of my overall site critiquing the “aquatic ape” idea. The idea doesn’t fare well under examination, I’m afraid. The AAT/H Characteristics List

  7. By: boltonian on March 21, 2008 at 9:57 pm      

    Anthrosciguy:

    Welcome and thanks for your contribution.

    I have no pretensions to detailed knowledge of the subject but I have read Morgan’s ‘Aquatic Ape Hypothesis,’ and Attenborough’s support thereof. I am merely an interested bystander.

    Curiously, your table does not convince me of the hypothesis’ fundamental error. If one takes the whole picture and compares it with those of alternative theories it stands up very well. Other things, including (if memory serves) vernix, shape of the nose and the lie of our hair all add substance to our aquatic origins.

    Picking individual components seems to me to miss the point and, as Morgan herself suggests, it is a hypothesis not a theory. It is not meant to be the last word on the subject.

    I would be very interested to hear your alternative hypothesis/theory together with the supporting evidence.

  8. By: chris on March 22, 2008 at 8:23 pm      

    A new hypothesis for evolution of bipedalism was featured earlier this month in New Scientist. Unfortunately, it’s behind the subscription wall, but the author’s website is worth a look :

    http://www.psom.blogspot.com/

  9. By: anthrosciguy on March 26, 2008 at 1:22 am      

    Curiously, your table does not convince me of the hypothesis’ fundamental error.

    I wouldn’t expect the table alone to do so, which is why I have a fairly extensive site on which it is merely one smallish page. What the table does is to point out that each of these claims is simply wrong — which for me kinda messes up the point the original was trying to make. And these are far from the only errors the idea’s proponents make, as my site shows.

    Perhaps the most fundamental error in the “aquatic ape” idea is that it insists that the world’s best mammalian environmental generalist got that way through physically adapting to one specific, and extreme, environment.

    A couple of points about your request for my take on human evolution. This, I feel, is a reasonable request if you want pointing to some valid info, but in my experience it’s often used to deflection attention away from the many massive flaws in the “aquatic ape” idea. Now I hope that’s not what you intend, and if it isn’t I hope you don’t take offense at this point: the validity of any theory does not depend to any degree on any other competing theory being valid or not. If every hypothesis on human evolution was shown to be wrong, it wouldn’t make the “aquatic ape” idea any less wrong.

    However, I see no reason not to feel that the Gathering Hypothesis (sometimes called Woman the Gatherer) is not correct; it’s been around for a long time and not only fit all the data when it was developed (largely from 1969-mid 1980s) but all since. For instance, the recent discover that savanna chimps used spears to hunt monkeys, and the fact that this was done mostly by females, fit perfectly into the Gathering Hypothesis. A good exposition of that idea can be found in many public libraries and used bookstores in Nancy Tanner’s 1981 book, On Becoming Human. There are other, shorter and somewhat older and newer versions, but their in journals and volumes usually only found in (some) university libraries.

  10. By: boltonian on March 26, 2008 at 2:38 pm      

    Anthrosciguy:

    I would just like to clear up a number of points implied in your last comment.

    I have no vested interest in the aquatic ape hypothethis other than that it seems a better explanation given the current state of (my) knowledge of the subject than others.

    I have not read your website in its entirety but I have (admittedly some years ago) read other explanations, all of which seem more unsatisfactory than the aquatic ape hypothesis.

    I think you might be reading too much into my request for your view and supporting evidence. Science advances through the formulation of hypotheses based on the available evidence, experimentation that verify amend or destroy the hypothesis, reformulation etc. I really am interested in your view as to the most likely explanation, particularly as you have some expertise in the field. But I am not interested simply in your opinion qua opinion. I would like to know, however, on what you base your view. As an analogy I think of the current state of theoretical physics. String theory is emphatically not a theory – it has not been verified through predictive experiment – but it is very fashionable and those engaged in other lines of research are finding great difficult in attracting funding. It is often said that string theory is the only game in town (by string theorists) but that is because it is mainstream and not because of its innate superiority. The aquatic ape hypothesis is not mainstream either and I would like to know whether it too is suffering from this prejudice of orthodoxy.

    Of course one can take the view that we do not know enough even to formulate hypotheses but sufficient only to know that none the the current conjectures is likely to be true. This is a postion some people are taking in the world of physics. But we could take that stance in anything as we can be certain of almost nothing. My brain needs some sort of of picture – I cannot visualise wholly negative or purely abstract ideas. So, I look at the world and ask, ‘What is the most likely scenario given the current (scant) state of our knowledge?’ But I know that this can change tomorrow as we accumulate a little more data. The enemy of learning is dogmatism.

    Returning to the subject, wasn’t the move to bipedalism so big, with all its attendant risks, that it must have been in response to extreme conditions? Why could not humans have specialised at a certain period in their development? It could be argued that we are still specialists, particularly in our social organisation which we have perfected to a far higher level of sophistication than other primates.

    I would also be interested in Biskie’s response to your comments as someone with far more knowledge on the subject than me.

  11. By: Biskie on March 26, 2008 at 11:06 pm      

    Boltonian and Anthrosciguy –

    I’m far from being an expert, just someone who has studied human evolution a bit (quite some time ago now) and still has a passing interest in the subject.

    My post was a rehashing of an old essay plus some notes from a talk I went to.

    I agree that the move to bipedalism must have come about due to extreme conditions. That no other primate is an habitual biped leads me to think this.

    As most people who have read anything that I have ever written would know, I do not invest a great deal of weight to *any* particular theory on *anything* (I am so open minded that my brain regularly falls out and I don’t actually care about it, I just scoop it back up and carry on). However, at the time I was looking into it, I did feel that the aquatic ape theory could well be of merit. That’s not to say that I wouldn’t consider looking at other theories.

    On a different subject, I’m interested in the Neanderthals and might try writing something about them soon.

    That’s if I manage to conquer my current Nintendo DS addiction.

  12. By: anthrosciguy on March 27, 2008 at 10:31 pm      

    I really am interested in your view as to the most likely explanation, particularly as you have some expertise in the field. But I am not interested simply in your opinion qua opinion. I would like to know, however, on what you base your view.

    I offered it; you can fairly easily find the book I mentioned, usually in a public library. (The refutation of the “aquatic ape” idea of course does not depend on the viability of any other viewpoint; theories either work or they don’t, they either make sense and follow the facts or they don’t, and the “aquatic ape” idea doesn’t. That’s not an opinion; I back it up on my site.)

    It’s common, especially to people who’ve read Morgan, to think that some big factor — usually environmental — forced bipedalism, but that doesn’t seem to be so. For one thing, we find that all primates use some bipedality, to varying degrees. Some, such as gibbons and siamangs, use it exclusively in terrestrial locomotion. But their background, an ape that uses brachiating as its primary movement, isn’t like our ancestors’ according to fossil evidence (although all apes, and humans for that matter, use brachiating — that’s what kids do on the monkey bars in playgrounds). And we find that the further back we look as we find earlier and earlier hominid fossils, they’re all bipedal. They used other forms of locomotion, as all primates do, but their fossils show they were effective bipedalists.

    To see why we look at how and when other primates use bipedalism, and also at the idea that bipedalism is terrifically difficult or energy consuming until you’re really built for it.

    The latter just isn’t so. Tests of chimpanzees show that even for them bipedalism is not more costly than quadrupedalism. This was a bit of a surprise when it was first tested. But it shows that it woulodn’t likely be a problem for early hominids, even earlier than we’ve found so far.

    When we look at when apes use bipedalism, the biggest reason, by far, is food-getting and carrying. Better observation is another, but not as much, as are indulging in displays, and a host of things. The data from wading is that bipedalism comes in handy sometimes there, but also that wading is not bipedal most of the time (by a fair margin). And it should be noted that wading alone is not the AAT/H; it simply doesn’t make sense — as its proponents insist — that an animal would wind up with the characteristics of fully aquatic mammals like whales, seals, and serenia through wading. (And then they’re wrong about those characteristics being the same, as my annotated list and other pages on my site show.)

    The bottom line, in as shorthand as I can get it, is that during the time of the transition there were several separated populations of last common ancestors (between apes and humans). Some used more quadrupedalism and some used more bipedalism, but both worked pretty well. In the same way we now see different populations of chimps do the same things different ways, for instance in how they fish for ants and termites, or how they open nuts (biting in some groups, hammering them with wood clubs in others, and hammering with stones in yet others). These all work fairly well, and it’s only after a lot of time that you see any significant differences in how useful any method or habit is.

    In our case we were in the lucky group; it happened that bipedalism allowed us, after many millions of years mind you, to use more tools in more ways, and develop both tools and food-getting to the point that larger braisn became useful enough for selection to not lop off that trait. (In animals the brain tends to wind up being about what they need and not more, because more brain means more energy to grow it and maintain it — if you don’t need a big brain, you’re better off having that energy go toward something else.) Now the ape side of the family, particularly chimps, did pretty well for a long time too, but in a more restricted set of environments. This worked great for them up until we got to the point where we had really effective weapons and massive numbers and habitat-altering abilities — a couple hundred years ago. After that they were in trouble, because of that lucky or unlucky break in the family (depending on which side you were on) many millions of years ago.

    People are often uncomfortable, I find, with the idea of chance and luck during evolution, but for us it was simply a lucky break that we were in the branch of the family that used more bipedalism, and the fact that it was lucky wasn’t so for several million years after it had happened. That’s luck.

    It could be argued that we are still specialists, particularly in our social organisation which we have perfected to a far higher level of sophistication than other primates.

    Yes, that was our specialization, not an environmental specialization as the AAT/H insists. The fact that we can, with our social and tool-making skills, use so many different environments is precisely because we were lucky enough to not physically adapt very much to any of them. Clifford Geertz put this well, I think, when he said “One of the most significant facts about us may finally be that we all begin with the natural equipment to live a thousand kinds of life but end in the end having lived only one.”

  13. By: boltonian on March 29, 2008 at 9:11 am      

    anthrosciguy:

    Thanks.

    I don’t think I can go any further with this discussion until I have read your book recommendation, which I will as soon as I can find the time.

    Please keep checking here and also feel free to contribute to any other thread that takes your eye.

    Biskie:

    A piece on Neanderthals would be very welcome.

  14. By: boltonian on March 30, 2008 at 9:52 pm      

    Anthrosciguy:

    I cannot find ‘On becoming Human’ (nor anything else by Nancy Tanner) in any bookshop or on Amazon.

    Can you please provide me with some more information, such as the publisher or ISBN.

    Thanks.

  15. By: boltonian on March 30, 2008 at 10:27 pm      

    Anthrosciguy:

    Call off the search – I tracked it down on a second hand book site.

  16. By: OutforTruth on April 1, 2008 at 4:20 am      

    I have to say that I’ve seen anthrosciguy post something negative in every forum on the net against the aquatic ape theory with some a level of spite that reminds me of the spanish inquisitors. He must be sitting at home google/blogs searching for any mention of Elaine Morgan or the Aquatic Ape theory and pouncing. Point he doesn’t have any scientific credentials and is somewhat of a kook. Be warned.

  17. By: boltonian on April 1, 2008 at 8:24 am      

    OutforTruth:

    Many thanks.

    Anthrosciguy:

    I have now read through substantial chunks of your website and, although I find the sarcastic and supercilious tone off-putting, there is nonetheless some interesting stuff. The whole tenor is so tendentious, however, that I will now need to re-read the Aquatic Ape Hypothesis (not theory) alongside the Tanner book that should be on its way to me right now.

  18. By: Martin on April 15, 2008 at 2:19 pm      

    I was thinking about the aquatic ape theory the other day, how there is a lack of clear evidence, and how similar theories could be constructed to explain the characteristics of, for example, elephants.

    Today I read: http://news.bbc.co.uk/2/hi/science/nature/7347284.stm

    Bible thumpers probably believe all animal life had an aquatic phase.

  19. By: boltonian on April 15, 2008 at 8:29 pm      

    Martin:

    I am currently reading Nancy Tanner’s book (see above) and will give my views once I have completed it.

    I would suggest that the Aquatic Ape thingy is an hypothesis rather than a theory.

    ‘Bible thumpers probably believe all animal life had an aquatic phase.’

    Why? Are you referring to Noah’s flood? If so, didn’t the animals that re-populated the earth find sanctuary in the ark?

    BTW you missed a good lunch.

  20. By: Janice Smith on September 26, 2011 at 8:18 am      

    Another theory of evolution? All right this is fine and the theory are at least relevant compared to the previous theory that I learned in my school time. I will dissect this info and try to connect it with other theory of evolution that I know.

  21. By: marc verhaegen on September 26, 2011 at 9:41 pm      

    Nice to see AAT discussed here, but duscussions should be about the recent insights in our waterside past: AAT has nothing to do with australopiths, but is about erectus-like Homo populations during the Pleistocene spreading to different continents & even islands (eg, Flores) along coasts (& from there inland along rivers) where they beach-combed & dived for aquatic & waterside foods, eg, shell+crayfish, turtles+eggs, stranded whales, drowned herbivores etc.
    See our 2011 paper “Pachyosteosclerosis suggests archaic Homo frequently collected sessile littoral foods” in HOMO – J compar hum Biol 62:237-247, or google “econiche Homo”.

  22. By: marc verhaegen on September 29, 2011 at 6:40 pm      

    For up-to-date papers on AAT, please also
    - google “econiche Homo”,
    - google “aquarboreal”,
    - read our forthcoming ebook “Was Man More Aquatic in the Past? Fifty Years after Alister Hardy: Waterside Hypotheses of Human Evolution” M.Vaneechoutte, A.Kuliukas & M.Verhaegen eds 2011 Bentham Sci.Publ., with contributions of Elaine Morgan, Phillip Tobias, Michel Odent, Anna Gislén & others,
    - or look at http://tech.groups.yahoo.com/group/AAT

  23. By: boltonian on December 7, 2011 at 2:02 pm      

    Thanks, Marc

  24. By: marc verhaegen on April 9, 2013 at 11:55 pm      

    FYI, some recent info on the littoral theory:

    - Human Evolution conference London 8–10 May 2013 with David Attenborough & Don Johanson
    http://www.royalmarsden.nhs.uk/education/education-conference-centre/study-days-conferences/pages/2013-evolution.aspx

    - guest post at Greg Laden’s blog
    scienceblogs.com/gregladen/2013/01/30/common-misconceptions-and-unproven-assumptions-about-the-aquatic-ape-theory/

    It’s now absolutely clear that Pleistocene Homo populations trekked along coasts & rivers. The only problems that remain are: how aquatic were they? how exactly did they live? what did they eat? where etc.

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