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Thread: Evolution of human bipedalism

  1. #1 Evolution of human bipedalism 
    Forum Bachelors Degree CEngelbrecht's Avatar
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    I am one to support the aquatic ape hypothesis to explain multiple unique features about human evolution. One of the stronger points is our vertical bipedalism, mimicking that of penguins.

    But apart of that, what other suggestions are there to explain moving from primate four to human two? I only know of Darwin considering a carrying behavior. Can anyone elaborate on that and other suggestions?


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    Of course all scientific evidence does not support it, but don't let that get in the way of your fantasy...


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    Forum Bachelors Degree CEngelbrecht's Avatar
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    Quote Originally Posted by MeteorWayne
    Of course all scientific evidence does not support it, but don't let that get in the way of your fantasy...
    That's a major problem, scientific evidence does support that 'fantasy', but aparently that seems to have very little to do with it.

    I'm trying very hard to keep my mind open for other options, even though I find it hard to see them make any sense anymore. If I'm so desperately wrong, then for the love of Darwin help me see it. Is anyone in here actually interested in a scientific debate, or is this all just human dominanse behavior?
    "The suppression of uncomfortable ideas may be common in religion or in politics, but it is not the path to knowledge, and there's no place for it in the endeavor of science. (History) shows us clearly that accepted and conventional ideas are often wrong, and that fundamental insights can arise from the most unexpected sources."
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    It's already been covered. Some of us are just bored repeating ourselves: http://www.thescienceforum.com/viewtopic.php?t=28828
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    In my opinion, the biggest problem with the aquatic primate theory of human evolution is the lack of supporting fossil evidence. Prehuman fossils exist, and none were laid down in marine sediments. Yet this is an excellent way to form fossils. Marine animals tend to leave vastly more fossils than land animals. If our ancestors had a habit of entering the sea to collect food, why did none die there and be preserved under marine sediments?

    My favourite theory for bipedalism is that it arose out of simple tool use. Wild chimps use tools such as stones to bash open nuts, grass stalks to tease out termites, large leaves folded to hold drinking water, and even short 'spears' for hunting. If our ancestors did all that, and then developed much better technology, then it makes sense that their bodies evolved to better use tools and weapons. This would include bipedalism to free the forelimbs for holding and using tools and weapons.

    If there is one thing that sets humans apart from the rest of the animal world, it is our use of sophisticated technology.
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    Quote Originally Posted by skeptic
    In my opinion, the biggest problem with the aquatic primate theory of human evolution is the lack of supporting fossil evidence. Prehuman fossils exist, and none were laid down in marine sediments.
    We have no transitional fossils at all, in any sediments. It seems likely the transition was fairly rapid and localized.

    And the marine sediments we have examined tend to be much older - they have to be raised from the water, dried out, etc, which is geological time.

    And the environment need not have been marine - seasonally flooded forest makes more sense, actually, for an ape to come down from the trees and start walking on its hind legs for some reason.
    Quote Originally Posted by skeptic
    My favourite theory for bipedalism is that it arose out of simple tool use.
    The better technology seems to require the bipedalism, not the other way around. And speaking of missing fossil data, we were fully bipedal (several species of us) long before any evidence of anything more sophisticated than a sharp rock shows up.
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    Hey guys, new here but been a stalker for a while... My understanding had always been that as the climate changed and grasslands were born, our ancestors were the ones to move out onto the plains, where height and bipedalism became an advantage. If you live an arboreal lifestyle, I can't think of any benefits afforded by being taller.

    And of course, it meant that our hands were free for tool use and to carry our belongings - which meant that we were better adjusted to the nomadic/migratory lifestyles of our prey than say our quadruped cousins were. The taller, bipedal individuals were more successful than the other strategies.
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    Quote Originally Posted by jaq835
    My understanding had always been that as the climate changed and grasslands were born, our ancestors were the ones to move out onto the plains, where height and bipedalism became an advantage.
    That's the traditional 'savannah theory' on human evolution. Problem is that the African grasslands were produced much later (~1 million years ago) than earliest known occurence of human bipedalism (Ardipithecus 4.4mya (Ardi is disputed, Lucy is surer 3.2mya)). The savannah theory is considered dead now and replaced by a so-called 'mosaic theory' in patches of woodland and open range (or an aquatic one, but that's aparently heavily disputed).
    "The suppression of uncomfortable ideas may be common in religion or in politics, but it is not the path to knowledge, and there's no place for it in the endeavor of science. (History) shows us clearly that accepted and conventional ideas are often wrong, and that fundamental insights can arise from the most unexpected sources."
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  10. #9  
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    Quote Originally Posted by skeptic
    In my opinion, the biggest problem with the aquatic primate theory of human evolution is the lack of supporting fossil evidence. Prehuman fossils exist, and none were laid down in marine sediments.
    Not exactly true. A specimen like Lucy (Australopithecus afarensis) was found in lake sediments and her habitat is genereally agreed to have been "lush and well watered" (her bones lay among crocodile and turtle eggs, and crab claws). Ardipithecus ramidus was found in sediments flanking the Awash River in Ethiopia. Even when Raymond Dart originally studied the Taung baby in 1924, he was presented with two boxes of fossils from an amateur collector. Quote: "Hoping for more primate fossils, Dart was disappointed after opening the first box, as it contained only fossilized egg shells, turtle shells and some bones [not for sure, but assumably from the same region]. However, as soon as he opened the second box he became elated. Sitting on top was an endocranial cast of a primate [the Taung baby]".
    http://www.suite101.com/content/raym...icanus-a328611
    Not that it's decisive aquatic evidence, as these few specimens of proto-humans may have only been preserved, because they happened to die at a body of water, and other specimens died inland without being preserved. But it's horrible if the dots are not being connected on this because of academic complacency.
    It could be interesting if someone studied on just how big a percentage of found proto-human specimens lived in then coastal regions. (Yeah, that'll happen ...)

    Quote Originally Posted by skeptic
    My favourite theory for bipedalism is that it arose out of simple tool use. Wild chimps use tools such as stones to bash open nuts, grass stalks to tease out termites, large leaves folded to hold drinking water, and even short 'spears' for hunting. If our ancestors did all that, and then developed much better technology, then it makes sense that their bodies evolved to better use tools and weapons. This would include bipedalism to free the forelimbs for holding and using tools and weapons.

    If there is one thing that sets humans apart from the rest of the animal world, it is our use of sophisticated technology.
    Some pointed out that wider use of technology beyond a sharp rock showed much later than earliest human bipedality, but a technology link is not impossible.

    Thereís also the case of observing the other great apes for bipedality. A Google pic search on 'standing chimp' or 'standing gorilla', Ďorangutaní, etc. does show that they can stand up on two, or though not habitually. In gorillas itís dominance behavior for males. It may not explain why human females also ended on two, but an angle towards some extention of dominance is also possible (ok, I donít buy it meself). Question is why chimps or orangutans stand up on two, and if that behavior may have been a key to habitual human bipedality.

    Sorry, Iím gonna rant into another pro-aqua perspective here, when talking about why and when chimps are up on two. It seems that chimps and other great apes tend to wade through water vertically on two:
    Gorilla: http://www.theregister.co.uk/2005/09...rilla_pool.jpg
    Gorilla: http://www.riverapes.com/Me/Work/Wal...s/image006.jpg
    Gorilla: http://www.riverapes.com/images/wadinggorilla.jpg
    Gorilla: http://cdn1.arkive.org/media/62/62FF...ugh-stream.jpg
    Chimp: http://img375.imageshack.us/img375/4443/wadinglf4.png
    Orangutan: http://www.chinadaily.com.cn/world/i...0b97fc191b.jpg
    Bonobo: http://anatomyofnorbiton.org/images/...ough-water.jpg
    Bonobo: http://i.telegraph.co.uk/multimedia/...k_1868081i.jpg
    Bonobo: http://www.shahrogersphotography.com.../LYB10-182.jpg
    Japanese macaque (technically a monkey): http://michaeljosephtherapy.com/blog...acaque_001.jpg
    Video of bathing chimp: http://www.youtube.com/watch?v=q916J6rzqno
    (Notice that itís snorting as it surfaces, because it hasnít developed a hooded nose like us to keep the water out of the skull.)

    As opposed to eg. wildebeest or hippos that stay on all fours in water, apes as a general trend move up on two in water. This is likely due to the primate subdivision of fore- and rear limbs into specific tasks, where the forelimbs interact with the surroundings, to pick food, carry young, and not always having ground contact like all quadrupeds. Compare to elephants, which interacts with the surroundings with its trunk, in primates as a group it is the forelimbs. That means that when these species move through water, they move to a vertical position so their forelimbs can still interact with the surroundings; carry food, young etc., as is being observed. The idea is then that in humans it became permanent, because beaches were our original habitat.

    Compare to penguins, which to my knowledge is a rare occurance of habitual vertical bipedality (granted, penguins are a large group of birds). As an aquatic bird, its forelimbs were originally specialized into glided flight, but are now adapted to aid propulsion underwater. They seek back towards land to flee from predators, mate and tend to offspring, and when they do, they move up to a vertical body position with a 180 degree angle between rear limbs and spine, as opposed to all other birds with a near-90 degree angle between rear limbs and spine. In early humans, a similar thing might have happened, in that the legs migrated from the chimp-like 90-degree angle between rear limbs and spine to a 180 degree angle in water, which then shows itself as a habitual upright vertical bipedalism when moving back on land.

    Sorry to bore you with this stuff. My intention is still to hear about the non-aquatic explantions (in case Iím crazy), even though I feel like Galileo arguing against the heliocentric universe.
    "The suppression of uncomfortable ideas may be common in religion or in politics, but it is not the path to knowledge, and there's no place for it in the endeavor of science. (History) shows us clearly that accepted and conventional ideas are often wrong, and that fundamental insights can arise from the most unexpected sources."
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    If you're not gonna say anything, you just confirm my perspective of being among the righteous on this topic.
    "The suppression of uncomfortable ideas may be common in religion or in politics, but it is not the path to knowledge, and there's no place for it in the endeavor of science. (History) shows us clearly that accepted and conventional ideas are often wrong, and that fundamental insights can arise from the most unexpected sources."
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  12. #11  
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    Quote Originally Posted by skeptic
    My favourite theory for bipedalism is that it arose out of simple tool use. Wild chimps use tools such as stones to bash open nuts...
    Chimps do not go bipedal when carrying or using tools. They walk on the knuckles of that hand carrying the object, and sit to use a tool. Even toting an awkward handful like a baby, chimps go on three legs.

    But I don't find theories for bipedalism mutually exclusive. There are numerous advantages to standing & walking upright; in my opinion all of them drove our adaptation. So the enhanced ability to forage shellfish and bash them open helps explain, and being poised to swing sticks at the damn babboons also helps explain.

    Quote Originally Posted by CEngelbrecht
    My intention is still to hear about the non-aquatic explantions (in case Iím crazy), even though I feel like Galileo arguing against the heliocentric universe.
    Bad analogy, because the truth of one bipedalism theory doesn't falsify another.
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    My understanding had always been that as the climate changed and grasslands were born, our ancestors were the ones to move out onto the plains, where height and bipedalism became an advantage.
    The problems with that are not just the timelines, as the stopgap "mosaic" environment is supposed to handle, but with the proposed transformation pressures: the advantages of bipedalism on a savannah require competent, structurally established, bipedal locomotion in the first place.

    A dog or baboon or squirrel gains nothing and suffers much from walking for long distances on its hind legs over a grassland, even "mosaic" stretches of grass between patches of woods.

    A quadrupedal ape can throw better, swing a club better, carry tools better, run faster and farther, and so forth, on three legs than on two, on four legs than on three. Whatever selection pressures drove the original transformation, they operated on a natural quadruped - there had to be some overwhelming advantage accruing to a naturally four-legged walker instead spending hours at a time every day, hundreds of days every year, and thousands of years consecutively, walking on its poorly adapted hind legs in defiance of its poorly adapted spine and hip and foot and internal organ structure, while the obviously overwhelming disadvantages were kept at bay.

    How that was supposed to happen on grassland patchwork or savannah environments, I have no idea.
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    Quote Originally Posted by CEngelbrecht
    Problem is that the African grasslands were produced much later (~1 million years ago) than earliest known occurence of human bipedalism (Ardipithecus 4.4mya (Ardi is disputed, Lucy is surer 3.2mya)).
    where do you get that piece of information from ? grasslands have been around in Africa since at least the Miocene
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Quote Originally Posted by iceaura
    swing a club better, carry tools better, run faster and farther, and so forth, on three legs than on two
    Ah, that part of the Sphinx's riddle: What goes on three legs?
    A: Man, with his walking stick.

    Until very recent times, man was commonly depicted with a staff. This aid to locomotion distinguished us from the other animals. So, given that we less-than-perfectly bipedal modern humans employ a stick, is it reasonable to imagine our early steps also got the same support? I think the hypothesis is testable. Evidence of habitual walking stick use should be in the wrist bones and rotation of the forearm.

    Inconclusively we can observe chimp behaviour: their posture while grasping sticks including upright branches. Chimpanzees typically dash for the branches when threatened. But the goal is not to climb - they grasp a vertical branch and swing around it, upright. There is safety in having a stick between oneself and one's foe, plus the branch supports a tall threatening posture. Normally the branch is shaken, sometimes it breaks off. Then instead of swinging around the stick, the chimp finds itself swinging a stick. Here the likening to our common ancestor must end, because while any sane human would hang onto that stick for continued protection, the chimp throws it wildly.

    It is pure speculation that our pre-bipedal ancestors felt safer with a good stick in hand, when crossing open areas. I don't think the behaviour would require planning or cultural learning - just that they might feel brave enough to risk it when they happened to be clutching what we'd later call walking sticks. It is unsubstantiated speculation that any one who dropped his stick while crossing the savannah would be quite helpless against hyenas even if he ran full speed on all fours. However it is easily tested by placing some naked modern humans in a Kenyan game park, amongst predators, one group with sticks and the other group without.
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    I don't think it's strictly accurate to refer to chimps and the like as quadrupeds (they are not complete terrestrial bipeds either). As with a great deal of things in biology, the definitions we impose on the natural world often refuse to fit neatly into our artificial pigeon holes. I would argue that chimps, and primates in general, exhibit a high degree of bipedalism. Watching chimps for any length of time (YouTube is an ideal venue) reveals that chimps move effortlessly and fluidly switching from four to three or two limbs continually. What the word for that is I don't know.

    Also worth pointing out that the "savanna" hypothesis and "mosaic" hypothesis are just that - hypotheses. A great deal of paleoanthropological evidence would suggest that we never left the forest at all.
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    Quote Originally Posted by Zwirko
    I don't think it's strictly accurate to refer to chimps and the like as quadrupeds... chimps move effortlessly and fluidly switching from four to three or two limbs continually.
    Very good point. Glad you made it.

    Could we say humans lost multipedalism?

    Quote Originally Posted by Zwirko
    A great deal of paleoanthropological evidence would suggest that we never left the forest at all.
    Well, the genetic plus circumstantial evidence is pretty conclusive. Chimpanzees have been adapting to better live in jungles. Since we share a common ancestor, that adaptation must be in contrast to ours. Now we're guessing whether they drove us out, or we drove them into the jungle, so our species diverged. I'd wager there were already cultural/technological differences driving the speciation, since both chimps and humans practice tribalism and sexual exclusivity to the point of genocide.

    I don't think it coincidence that the reclusive black chimpanzee (bonobo) is less in competition with our species and more bipedal than common chimpanzees.
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    Quote Originally Posted by marnixR
    Quote Originally Posted by CEngelbrecht
    Problem is that the African grasslands were produced much later (~1 million years ago) than earliest known occurence of human bipedalism (Ardipithecus 4.4mya (Ardi is disputed, Lucy is surer 3.2mya)).
    where do you get that piece of information from ? grasslands have been around in Africa since at least the Miocene
    I know, but not in the locations where proto-humans have been found, eg. the Afar Depression in Ethiopia.

    Example:
    http://www.mudfirst.net/articles/emm...ipedalism2.htm
    Quote: Most evidence suggests that bipedalism developed long before the drastic change in African ecology from forest to savannah (Jacobs, 2000).
    "The suppression of uncomfortable ideas may be common in religion or in politics, but it is not the path to knowledge, and there's no place for it in the endeavor of science. (History) shows us clearly that accepted and conventional ideas are often wrong, and that fundamental insights can arise from the most unexpected sources."
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    Quote Originally Posted by pong
    So, given that we less-than-perfectly bipedal modern humans employ a stick, is it reasonable to imagine our early steps also got the same support?
    Not even humans use walking sticks until old age or other infirmity.

    By the time we were tool using bipeds capable of reaching old age, we had been bipedal for a very long time.
    Quote Originally Posted by pong
    It is pure speculation that our pre-bipedal ancestors felt safer with a good stick in hand, when crossing open areas.
    Attempting to posit unexplained mental attitudes that cause animals to behave oddly and self-abusively, as a species-wide and millenia-standard behavior in the face of all its malign effects (high rates of leopard predation, slower and less efficient locomotion, greater rates of injury and incapacitation, etc), would be a last resort.

    Only if forced, by overwhelming evidence. And it isn't.

    When modern chimps enter dangerous country on foot, they get low and pack together. That makes sense.
    Quote Originally Posted by zwirko
    I would argue that chimps, and primates in general, exhibit a high degree of bipedalism. Watching chimps for any length of time (YouTube is an ideal venue) reveals that chimps move effortlessly and fluidly switching from four to three or two limbs continually.
    They do not walk effortlessly and fluidly on two legs for any distance. They lack the skeletal modifications necessary for efficient bipedal locomotion. They possess the skeletal structures of a quadruped primate, and it's difficult to describe circumstances in which they would voluntarily spend hours walking on their hind legs in pursuit of some very significant selection or reproduction advantage ( The Youtube videos are biased toward the circumstances of videography - chimps hanging around in a small area, playing and stuff. )

    Lots of quadrupeds spend considerable time on two legs - raccoons, rabbits, monkeys, squirrels, (put a stopwatch on a squirrel foraging acorns - it spends a fair amount of time fluidly and effortlessly on its hind legs holding nuts to its mouth).
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    Iceaura, most of what you responded to I did not in fact say.



    They do move effortlessly and fluidly switching from 2 to 3 to 4 limbs continually. I never made mention of long distances or long time frames, neither did I say that they walk on two legs for any sort of distance or for how long. The effortless and fluid motion I refer to is the smooth and constant shifting from 2 to 3 to 4 limbs that chimps often exhibit. Chimps do in fact display a high degree of bipedal behavior and I'm well aware that they are not complete terrestrial bipeds - the pointless point I'm making is that the simple categories we use fail to capture the nuances of locomotion observed in modern day primates such as chimps. If we go away thinking that chimps move only on four limbs, then we have missed something of great importance. To repeat: I'm not reclassifying chimps as bipeds.

    The bipedal behaviors of modern day non-human primates have a great deal of relevance to the evolution of complete terrestrial bipedality in humans and in other extinct primates; the skeletal and muscular anatomies that facilitate such behaviors are major pre-adaptations to complete bipedality and the ecological/behavioral settings under which it evolved and continued to evolve is of interest here.
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    Quote Originally Posted by iceaura
    When modern chimps enter dangerous country on foot, they get low and pack together. That makes sense.
    That's one strategy, though not recommended for human hikers. Hikers are advised to walk tall and make their presence known. Survivals of black bear attacks teach that you'll want a stick, and you'll want it for fighting back.

    Chimpanzees provide insight of our common ancestor, but one can overdo it: remember that while we've evolved in our ways, they've evolved in theirs. Chimps represent an ongoing and alternate course of evolution, not our ancestors.

    Are you suggesting that modern humans and modern chimps use sticks as tools & weapons, but our common ancestor didn't (or if they did it was "self-abusive" :P )? I'm assuming that we did at least as often as chimps do today. From there I'm speculating that some groups (a cultural difference to start) began to rely more on sticks and wouldn't quickly toss them away as chimps will.

    Then, often going on three legs with a stick in hand, helps explain the change in posture. This hypothesis may be supported by appropriate changes in wrist anatomy, but I'm unqualified to determine that.
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    Quote Originally Posted by zwirko
    I never made mention of long distances or long time frames, neither did I say that they walk on two legs for any sort of distance or for how long.
    And I pointed that out, observing that the omission begs the question before us.

    Chimps are quadrupeds, meaning that when they walk any great distance they do so on four limbs and are built that way. The evolutionary changes in skeletal and organic structure necessary for bipedalism - walking on two legs as one's standard mode of locomotion over the distances one ordinarily walks - are exactly what we are trying to explain.
    Quote Originally Posted by pong
    That's one strategy, though not recommended for human hikers. Hikers are advised to walk tall and make their presence known. Survivals of black bear attacks teach that you'll want a stick, and you'll want it for fighting back.
    Humans are tool using bipeds. They evolved from ape-structured quadrupeds. The transition from that starting point is what we are trying to explain. We need an explanation that works for quadrupedal apes, not bipedal humans.
    Then, often going on three legs with a stick in hand, helps explain the change in posture.
    How?

    Going on three limbs to carry a stick is a quadrupedal strategy, and relies on quadrupedal musculature and skeletal structure - to the extent it works, it blocks any transition to bipedalism. To the extent it doesn't work, it won't be employed.
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    Forgive me if I'm being dense: Going on three limbs to carry a stick is tripedal, not quadrupedal. How does 3 "block any transition" from 4 to 2?

    ***

    Your argument against Zwirko's point depends on "walking a great distance", like if you put an orb spider on a floor it must walk proving one form of locomotion. We know chimpanzees seldom walk a great distance. Their normal mode employs any number of limbs, and I'll add that besides the 2, 3, 4 mentioned chimps also use 1 to reach and swing a short distance, and they roll over, and even employ somersaults or shuffling on their butts. They do not normally walk a great distance by any means.
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