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Thread: Our Legs

  1. #1 Our Legs 
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    Isn't the generally accepted theory of why we evolved to be erect on two feet was to move large distances quicker and more efficently, while migrationg across africa.

    Lion top speed: 35mph
    cheetah: 60mph
    human: about 25 mph

    It seems to me like 4 legs is faster, but mabey not more efficeint.

    So is having two legs faster and more efficeint is my question


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    you need to compare our locomotion with that of our nearest relatives, the chimps and the gorillas - does bipedal gait represent an advance over knuckle walking for doing long-distance in a savannah environment ?


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  4. #3 Re: Our Legs 
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    Quote Originally Posted by Jon not Ron
    Isn't the generally accepted theory of why we evolved to be erect on two feet was to move large distances quicker and more efficently, while migrationg across africa.

    Lion top speed: 35mph
    cheetah: 60mph
    human: about 25 mph

    It seems to me like 4 legs is faster, but mabey not more efficeint.

    So is having two legs faster and more efficeint is my question
    Many people think that had something to do with it, but the situation is more complex than is usually portrayed by popular media.

    The first bipedal species for whom we have a decent skeleton is the famous Lucy, Australopithecus afarensis. However, Lucy's skeleton is far from the specialized bipedal skeleton modern humans have. She exhibits what is often called a compromise morphology - not fully quadrupedal, but not like modern humans either. So the question has long been: in this compromise form, is bipedalism more efficient than quadrupedalism? If efficiency was a major selective force in the evolution of bipedalism, then it must be. But was it?

    It's difficult to measure exactly how efficient Lucy's gait may have been based on a skeleton alone. We're still unsure exactly how she would have moved; many advocate a "bent-hip, bent-knee" posture, which sounds very inefficient. Most tests, then, are done comparing the efficiency of a chimpanzee walking bipedally, a chimpanzee walking quadrupedally, and a human walking (bipedally of course). The most recent study of this nature was done here:

    http://www.pnas.org/content/104/30/12265.full

    Modern human bipedality wins by far in terms of efficiency, but that goes without saying. What this study found is that, on average, quadrupedal chimps are more efficient than bipedal chimps. However, their sample was only made up 10 individuals, and interestingly one of those individuals showed greater efficiency walking bipedally than they did walking quadupedally. This paper shows that small individual differences in things like stride length and knee flexion can make even a largely quadrupedal morphology like chimp's be more efficient in a bipedal mode.

    Considering that though Lucy is less bipedal than modern humans but more bipedal than modern chimps, I'm inclined to say her bipedal gait may have been more efficient. But it's still hard to know for sure, and it's hard to know if the difference in efficiency was big enough to form a strong selective pressure for bipedalism. I'm of the opinion that it was a combination of factors, of which efficiency was only one, but did contribute.
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    The hypothesis that bipedalism allows greater tool use is an attractive one, which has nothing to do with efficient locomotion.
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    The first bipedal precursor to humans was Orrorin tugenensis, which preceded Lucy by 3 million years - ie 6 million years ago.
    http://en.wikipedia.org/wiki/Orrorin_tugenensis

    So bipedalism has been around a long time. Orrorin and Lucy both climbed trees also, but probably spent a lot of time on the ground. Computer studies have shown that bipedal locomotion is more energy saving that the knucking method used by chimps and gorillas.

    However, as Paralith said, it is unlikely to be that simple. Other benefits also accrue from bipedalism, including the freeing of the fore limbs to become tool users and carriers.
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  7. #6  
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    Quote Originally Posted by skeptic
    The first bipedal precursor to humans was Orrorin tugenensis, which preceded Lucy by 3 million years - ie 6 million years ago.
    http://en.wikipedia.org/wiki/Orrorin_tugenensis

    So bipedalism has been around a long time. Orrorin and Lucy both climbed trees also, but probably spent a lot of time on the ground. Computer studies have shown that bipedal locomotion is more energy saving that the knucking method used by chimps and gorillas.
    We only have fragments of a femur for Orrorin, and it is based on this alone that it is claimed to be bipedal. It has several characters which you would find in bipedalism, but that you might also find in quadrupeds as well. I would hesitate to conclude with any great certainty that Orrorin was bipedal, and even if it is we have very little idea of what kind of bipedality it was capable of due to the lack of fossils. Thus Orrorin is not informative when discussing the efficiency hypothesis of bipedality.

    If we want to speculate on the oldest potentially bipedal ancestor, Sahelanthropus chadensis is also a contender at possibly 7 mya (the skull is highly deformed but a computer reconstruction suggested a formen magnum position under the skull instead of at the back of the skull). And if you really want to stretch it, Aaron Filler believes that Morotopithecus bishopi, a 21 mya miocene ape, was also bipedal. His analysis is based on a single lumbar vertebra and is, by far, the most speculative.

    However, as Paralith said, it is unlikely to be that simple. Other benefits also accrue from bipedalism, including the freeing of the fore limbs to become tool users and carriers.
    This may have contributed to the maintenance of bipedality, but most certainly not to its original evolutionary advent. The first verifiable stone tool user was Australopithecus garhi that lived 2.5 mya, well after bipedality first appeared, and who's to say whether or not tool use was important enough to this particular species to form a selective pressure on their posture. Remember, chimps also make and use tools, but not in a way that requires or is significantly improved by bipedality.
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    The problem with discussing when tool use began, is that the first fossil evidence of tools comes with chipped stone. However, the use of unmodified objects as tools would, no doubt, precede the manufacture of chipped stone by a very long period. If an antelope jawbone is found near an Australopithecus fossil, is that evidence of tool use? Sadly, we cannot tell.
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    Quote Originally Posted by skeptic
    The problem with discussing when tool use began, is that the first fossil evidence of tools comes with chipped stone. However, the use of unmodified objects as tools would, no doubt, precede the manufacture of chipped stone by a very long period. If an antelope jawbone is found near an Australopithecus fossil, is that evidence of tool use? Sadly, we cannot tell.
    If the jawbone appears to have wear marks that are not typical of predatory feeding, then yes, perhaps it is. I will not deny that estimations of tool use are extremely difficult given the overall lack of evidence, so let me revise my previous statement: I think it less likely that tool use was important enough to the first bipedal species to form a significant selective pressure of any kind on posture since no suggestions of tool use have ever been found with such species. Not impossible, just less likely.
    Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
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    no Bipedal movement did not evolve for faster migration you are being to narrow minded


    things evolve for various reasons and once a reason becomes unneccessary the evolved thing won't change much untill it is required to, for example A Tiger that for some reason gets stuck in an area where the primary foodsource is very toughskinned and difficult to kill, Over time the species develop long sharp teeth (sabertooth) and then if the tigers somehow get trapped somewhere where the main prey are fleshy mammals and long pointy teeth are no longer neccessary the teeth don't go away, they stay even though they arn't needed anymore

    Bipedal legs I would assume evolved for a variety of reasons the main being free hands giving the ability to quickly climb, a straightened spine evolved for a height advantage, When brainsize grew exponentially the need for climbing disapeared and two legs did not


    Plus there is the larger point, Cheetahs can run at 60kmph for 60 seconds there is a tribe that run at 25kmph and can run non-stop for over 150 miles, (it's how they hunt, the chase a deer for so long the deer collapses from exhastion before they do) this tribe is very close to early man
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    Quote Originally Posted by Booms
    there is a tribe that run at 25kmph and can run non-stop for over 150 miles, (it's how they hunt, the chase a deer for so long the deer collapses from exhastion before they do) this tribe is very close to early man
    Is that 25,000 mph? - either way you are a little out these hunters merely walk (or at best 'jog') to catch their prey, the prey runs for a while and when it feels safe it it will stop, after a while the hunter catches up and the process repeats until the animal is exhausted. As an example try running as fast as you can for 1/4 mile or so, at the end of this you will have used far more energy and be far more tired than if you simply walked the same distance.
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    Quote Originally Posted by Booms
    Bipedal legs I would assume evolved for a variety of reasons the main being free hands giving the ability to quickly climb, a straightened spine evolved for a height advantage, When brainsize grew exponentially the need for climbing disapeared and two legs did not
    Booms, if bipedalism "free hands giving the ability to quickly climb," then why are all the other apes still quadrupedal? I think it's safe to say chimpanzees can climb better and quicker than we can.

    The height advantage hypothesis was related to allowing early human ancestors to see over tall grasses; unfortunately, this hypothesis assumes bipedalism evolved in the savannah and it did not. It evolved in forests and woodlands - not as thick as jungles but most certainly not grasslands.

    And what does brain size have to do with the need for climbing? I don't quite understand that reference.

    Plus there is the larger point, Cheetahs can run at 60kmph for 60 seconds there is a tribe that run at 25kmph and can run non-stop for over 150 miles, (it's how they hunt, the chase a deer for so long the deer collapses from exhastion before they do) this tribe is very close to early man
    Quote Originally Posted by wert
    Is that 25,000 mph? - either way you are a little out these hunters merely walk (or at best 'jog') to catch their prey, the prey runs for a while and when it feels safe it it will stop, after a while the hunter catches up and the process repeats until the animal is exhausted. As an example try running as fast as you can for 1/4 mile or so, at the end of this you will have used far more energy and be far more tired than if you simply walked the same distance.
    What I think Booms is trying to refer to is persistence hunting, a form of hunting used by, among others, the hunter-gatherer Hadza in Ethiopia. Basically, they follow a single animal constantly, forcing that animal to run constantly until it drops down from pure exhaustion.

    However, this is unrelated to the advent of bipedalism. It is related to the endurance running hypothesis which is about the more modern human bipedal form, specifically that found in Homo erectus. Two researchers, Bramble and Lieberman, put forward the theory that this species evolved to run, not for speed, but for very long distances. Again, it is a matter of efficiency. The largest problem with their hypothesis is that there hasn't been a very strong case for why this would evolve.

    Some people have pointed to persistence hunting and said, THAT is why they evolved it! But persistence hunting is extremely difficult, time consuming, potentially dangerous, and some argue that erectus may not have had the mental capacity to carry out the type of tracking required for persistence hunting. Most of the time you are not actually in sight of the animal, but following its tracks. Nor is persistence hunting the main form of hunting used by any modern hunter gatherer.

    You always have to be a little careful when comparing hunter gatherers to early humans, however; remember that though their lifestyle is probably quite similar that are not early humans themselves, and have probably undergone changes of their own since that time.
    Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
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    i think we can all agree that bipedalism developed while we were still living in a wooded environment (e.g. Ardipithecus)
    so maybe there was no particular reason why it developed and established itself in a small population of chimp-like apes, but once the woods turned into wooded savannah this fortuitous trait may have turned out to be advantageous
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    I personally think that persistence hunting was a result of the earliest clothing. A big problem with persistence is the need to dump large amounts of heat. Those that cannot, will quickly become exhausted through over-heating. However, at some stage our prehuman ancestors lost their fur. Without clothing, this would have rapidly led to hypothermia, even in the tropics, on those early morning accasions when it got cold. However, the use of clothing or clothing substitutes would permit fur loss without risk of hypothermia.

    Once fur is lost, persistence hunting becomes more fesible, since bare skin permits extremely efficient dumping of heat.
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    I personally think that persistence hunting was a result of the earliest clothing. A big problem with persistence is the need to dump large amounts of heat. Those that cannot, will quickly become exhausted through over-heating. However, at some stage our prehuman ancestors lost their fur. Without clothing, this would have rapidly led to hypothermia, even in the tropics, on those early morning occasions when it got cold. However, the use of clothing or clothing substitutes would permit fur loss without risk of hypothermia.

    Once fur is lost, persistence hunting becomes more feasible, since bare skin permits extremely efficient dumping of heat.
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    I don't think persistence hunting is required to make the loss of fur adaptive. Simply being active during the hottest part of the day, which most animals are not, would be reason enough.
    Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
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    As I am sure you are well aware, Paralith, an evolutionary change may be driven by more than one cause. Persistence hunting and heat of the day - both. Sure, I agree. In fact, if we think about it, I am sure we come up with even more advantages to improving the ability to dump heat.

    The point I was making, really, is that this advantage would follow the invention of clothing, or other artificial means of keeping warm.

    If tool use is a driver of bipedalism, this would mean another technological advance driving another evolutionary change.
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    Seems we had many good reasons to become bipedal. This needn't be either/or.

    One advantage not mentioned yet, is in the predator's eyes. Many species have accentuated traits simply to announce what they are to other species. Look I'm plainly a skunk - go snarl elsewhere. Hiss - I'm a venomous snake. Etc.

    Judging by our cousins we had little trouble dealing with predators. We, as they, probably waved our arms, hooting and throwing objects. The predators learn to avoid this abuse - confronting us just isn't profitable. So becoming a caricature of our unique displays would be advantageous, especially the passive one: standing erect. Note that animals today are clearly most afraid when we stand and walk on two legs. If that isn't enough, we instinctively frighten bothersome animals by raising our arms and shouting, just as the chimps do but more characteristically. It's a warning pose. Hikers purposefully talk and sing in the forest, even alone, so bears hearing the distinctly human voice may make a dignified early exit rather than meet a human face to face.

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    Quote Originally Posted by Booms
    Plus there is the larger point, Cheetahs can run at 60kmph for 60 seconds there is a tribe that run at 25kmph and can run non-stop for over 150 miles, (it's how they hunt, the chase a deer for so long the deer collapses from exhastion before they do) this tribe is very close to early man
    I'm going to have to call BS on this. The current world record for a marathon is only about 20 kph, sustained for only 40 km.
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    Two legs is actually more efficatious as far as long distances are concerned, which people are champions, at least as far as I heard.
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  21. #20  
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    Quote Originally Posted by Scifor Refugee
    Quote Originally Posted by Booms
    Plus there is the larger point, Cheetahs can run at 60kmph for 60 seconds there is a tribe that run at 25kmph and can run non-stop for over 150 miles, (it's how they hunt, the chase a deer for so long the deer collapses from exhastion before they do) this tribe is very close to early man
    I'm going to have to call BS on this. The current world record for a marathon is only about 20 kph, sustained for only 40 km.
    I think the record is something like 147.6km in 12 hours.
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