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Thread: Evolution of Bipedalism

  1. #1 Evolution of Bipedalism 
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    This is a video I made for my Human Anthropology class. It talks about how animals that walked on 4 feet, evolved into animals that walk on 2 feet... THere are some funny moments in the video. Check it out if you wanna learn something!!

    http://www.youtube.com/watch?v=-g7Inj62Axk


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    So did you want to start a discussion about this or...what, exactly? Paralith would be a great person to wait for (she'll be around soon) to talk to about all this, she's pretty damn smart.

    I'm glad to see you and your homie Jamal did some research on the internet and all that stuff, was this a university course? I'm guessing a first year kind of thing, there are always fun projects in intro courses it seems.

    Also, welcome to the forum, I haven't seen you around here before.


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    I really liked the video. Pretty funny
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    Disclaimer: I'm being nitpicky because this is a class assignment, and if it is at all possible for the OP to make some corrections before handing it in, I'd like to help him out.

    Technically, the hominids is a classification that contains all the great apes. The hominan is the classification that contains only the line that eventually lead to us, if you wanna get picky. There is no classification that consists only of the hominans that existed approximately 6 million years ago; a more exact term might be early Australopithecines, or even Ardepithecines if you think ramidus merits its own genus.

    The seeing-over-the-grass hypothesis has come into disfavor lately because the earliest bipeds did not live in true savannahs, but in woodlands. Not the thick jungles of chimps, mind you - they were more open and may have contained patches of grass, but probably not the tall grasses you see in the plains. Incidentally, there are other animals that stand upright momentarily to get a good view, like meerkats, but that wasn't enough to make them move bipedally. Why would it be enough for Australopithecines?

    Chimp males do on occasion stand up and run around in order to intimidate each other, but it's not something that attracts a female chimp. In fact, the male may actually be running at her just prior to beating her, in order to scare her out of the idea of mating with any other male besides him. There is no evidence that standing tall attracts females, at least not in chimpanzees.

    And, if you're using chimpanzees as your model for the Australopithecines, chimp males don't do squat for chimp females. She's all on her own when it comes to getting food. Was the same true for Australopithecine males? We really don't know, but I'm inclined to think that at that point they probably weren't too different from most apes, and probably did not provision females at all. Nor is there any evidence of stone tool use until around 4 mya, so they probably didn't use tools enough to justify becoming bipedal for them.
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    My understanding is that bipedalism evolved as a means for marathon movement. The great apes which travel on all fours have a more limited range than humans. Ancient humans needed to be able to travel long distances efficiently, and since they started with a great ape physiology, bipedalism was the more likely outcome. (Similar to how kangaroo hoping is more efficient than horse trotting, but horses aren't likely to learn how to hop because they start out with horse physiology).

    I could be mistaken, of course, but that's the explanation I understand.
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    it probably had something to do with line of sight as well
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    Quote Originally Posted by paralith
    Chimp males do on occasion stand up and run around in order to intimidate each other, but it's not something that attracts a female chimp. In fact, the male may actually be running at her just prior to beating her, in order to scare her out of the idea of mating with any other male besides him. There is no evidence that standing tall attracts females, at least not in chimpanzees.
    Yup, yet I think Mikey, flaunting his bipedalism, was onto something. He's making plain his species, to anyone or anything that's watching. Notice birds don't land near Mikey. They know man. Wild animals see Mickey walking tall and they think: "Man!" and run away.
    A pong by any other name is still a pong. -williampinn
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    Quote Originally Posted by paralith
    Disclaimer: I'm being nitpicky because this is a class assignment, and if it is at all possible for the OP to make some corrections before handing it in, I'd like to help him out.

    Technically, the hominids is a classification that contains all the great apes. The hominan is the classification that contains only the line that eventually lead to us, if you wanna get picky. There is no classification that consists only of the hominans that existed approximately 6 million years ago; a more exact term might be early Australopithecines, or even Ardepithecines if you think ramidus merits its own genus.

    The seeing-over-the-grass hypothesis has come into disfavor lately because the earliest bipeds did not live in true savannahs, but in woodlands. Not the thick jungles of chimps, mind you - they were more open and may have contained patches of grass, but probably not the tall grasses you see in the plains. Incidentally, there are other animals that stand upright momentarily to get a good view, like meerkats, but that wasn't enough to make them move bipedally. Why would it be enough for Australopithecines?

    Chimp males do on occasion stand up and run around in order to intimidate each other, but it's not something that attracts a female chimp. In fact, the male may actually be running at her just prior to beating her, in order to scare her out of the idea of mating with any other male besides him. There is no evidence that standing tall attracts females, at least not in chimpanzees.

    And, if you're using chimpanzees as your model for the Australopithecines, chimp males don't do squat for chimp females. She's all on her own when it comes to getting food. Was the same true for Australopithecine males? We really don't know, but I'm inclined to think that at that point they probably weren't too different from most apes, and probably did not provision females at all. Nor is there any evidence of stone tool use until around 4 mya, so they probably didn't use tools enough to justify becoming bipedal for them.
    I thought the term was hominins not hominans?
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    Quote Originally Posted by Numsgil
    My understanding is that bipedalism evolved as a means for marathon movement. The great apes which travel on all fours have a more limited range than humans. Ancient humans needed to be able to travel long distances efficiently, and since they started with a great ape physiology, bipedalism was the more likely outcome. (Similar to how kangaroo hoping is more efficient than horse trotting, but horses aren't likely to learn how to hop because they start out with horse physiology).

    I could be mistaken, of course, but that's the explanation I understand.
    That is my understanding also. I think it sounds most logical. Especially if you compare the genome of chimps to humans... you can see certain fitness genes that we have and they do not. If you use the program below you can easily compare any gene to other animals. If it is highly conserved then it is likely that it was important for hominin evolution. If it is not conserved or it is different then I guess you can work out what's changed. I think I explained that poorly... but you get the idea right?

    Have a go. Type AMPK (This is an energy sensor in cells that is very important as it can be found in all eukaryotes).

    http://ecrbrowser.dcode.org/
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    hominans
    Those are their grandmothers.
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    I've always thought bipedalism came about as a result of foraging in open grassland. I made a post on facebook concerning this. I'll post some of it here:

    Recent geological evidence has shown that millions of years ago Africa began turning from a lush jungle area to a desert climate through desertification and that areas between different jungle environments were separated by vast stretches of savanna. It is my belief (Although I'm fairly certain this has been proposed before) that our ancient mammalian ancestors lived on the borders of these jungle/savanna wildernesses. To forage and hunt for food they needed to travel outside of the safety of the jungle, both armed with weapons such as sticks or clubs and in packs, to gather what they needed. Having a weapon in one hand and a pile of food in the other didn't really allow for movement on all fours. They needed to walk bipedally back to the safety of the jungle. Eventually their bipedalism grew enabling them to carry more food as well as enabling them to protect themselves better. With bipedalism becoming more common it allowed our ancestors to free up their hands which would then provide them the means of more tool use, better tools and subsequently bigger brains.

    The original post goes on to explain how this would then lead into loss of body hair and then to darkening of the skin which, when humans began moving northward, became lighter to allow absorption of Vitamin D.
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    Numsgil and Molecular:
    That is one of the prevailing ideas, but the problem is that the very first bipedal species were not bipedal like you or me - they have what is called a compromise morphology, somewhere between chimpanzees and humans. It has long been an issue of contention whether or not this morphology is actually more efficient when moving bipedally compared to moving quadrupedally. It's hard to tell exactly how Lucy moved, and some think she had a "bent knee bent hip" stride that doesn't seem very efficient at all. The later species, especially Homo erectus, develop a more modern bipedalism are most certainly more efficient (and the fitness genes Molecular mentions may have evolved with this species and not previous ones - are there divergence dates on these gens?) - the question is, was efficiency a major driving force at the very advent of bipedalism? It's hard to say.

    Pong:
    There are some who think bipedalism evolved in order for groups of humans to intimidate predators off their kills, giving them access to the meat. But again we have to understand exactly what the first bipeds were like: Lucy wasn't much taller than a chimp would be if it stood up. Is that enough to scare a predator like a lion or a hyena? And again, she didn't live in the open savannah, she lived in woodlands. Would she encounter those types of predators there? It's very well possible that she may have, these are just unanswered questions.

    BumFulff:
    Again, Lucy did not live in the savannah, she lived in woodlands. Granted, some of these woodlands appear to have bordered more open areas, but very few specimens are found with evidence of that type of environment. Also, her use of tools is another issue of debate. The first evidence of stone tool use happens with Australopithecus garhi, about a million years after Lucy is on the scene. This of course doesn't necessarily mean Lucy didn't use tools, especially of the wooden, biodegradable sort, but how much did she use them? How important were they to her survival? Was their use a primary driver of bipedalism? Again, it's hard to say.



    If there is one thing I have learned about paleoanthropology, it's that the actual state of knowledge on many of these issues is much less certain than is often portrayed in undergraduate classes and popular media. When dealing with fossil animals like these the amount of data is so limited that it is very difficult to make sound conclusions. Half or more of what I said above may be turned on its head in the coming years by the discovery of a new fossil or two. I would just like to caution all of you to maintain a healthy degree of skepticism when it comes to these things, and to understand that all the postulation in the world is no good without the evidence to support it.
    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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    Quote Originally Posted by paralith
    Numsgil and Molecular:
    That is one of the prevailing ideas, but the problem is that the very first bipedal species were not bipedal like you or me - they have what is called a compromise morphology, somewhere between chimpanzees and humans. It has long been an issue of contention whether or not this morphology is actually more efficient when moving bipedally compared to moving quadrupedally. It's hard to tell exactly how Lucy moved, and some think she had a "bent knee bent hip" stride that doesn't seem very efficient at all. The later species, especially Homo erectus, develop a more modern bipedalism are most certainly more efficient (and the fitness genes Molecular mentions may have evolved with this species and not previous ones - are there divergence dates on these gens?) - the question is, was efficiency a major driving force at the very advent of bipedalism? It's hard to say.

    Pong:
    There are some who think bipedalism evolved in order for groups of humans to intimidate predators off their kills, giving them access to the meat. But again we have to understand exactly what the first bipeds were like: Lucy wasn't much taller than a chimp would be if it stood up. Is that enough to scare a predator like a lion or a hyena? And again, she didn't live in the open savannah, she lived in woodlands. Would she encounter those types of predators there? It's very well possible that she may have, these are just unanswered questions.

    BumFulff:
    Again, Lucy did not live in the savannah, she lived in woodlands. Granted, some of these woodlands appear to have bordered more open areas, but very few specimens are found with evidence of that type of environment. Also, her use of tools is another issue of debate. The first evidence of stone tool use happens with Australopithecus garhi, about a million years after Lucy is on the scene. This of course doesn't necessarily mean Lucy didn't use tools, especially of the wooden, biodegradable sort, but how much did she use them? How important were they to her survival? Was their use a primary driver of bipedalism? Again, it's hard to say.



    If there is one thing I have learned about paleoanthropology, it's that the actual state of knowledge on many of these issues is much less certain than is often portrayed in undergraduate classes and popular media. When dealing with fossil animals like these the amount of data is so limited that it is very difficult to make sound conclusions. Half or more of what I said above may be turned on its head in the coming years by the discovery of a new fossil or two. I would just like to caution all of you to maintain a healthy degree of skepticism when it comes to these things, and to understand that all the postulation in the world is no good without the evidence to support it.
    Thanks for your post and information that is great. There are limited known fitness genes at present. I am aware that a new gene map has very recently been published (Gene Map For Human Performance and Health) so we can hope there are some that are comparatively different.

    I understand and there is proof of a correlation between bipedalism and losing the function of the myosin heavy chain 16 gene (jaw muscle gene) which is present in all apes but not present (or not functioning) in all humans across the world. They think that this mutation caused the muscles of the jaw to attach at a different place which allowed for the brain to grow larger. This has been correlated to 1.7 million years ago.
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    OP- I just know that the discovery of Lucy in '74 proved the hypothesis that big brains led to bipedalism wrong. I'm unsure of what the current state of affairs concerning this is...
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    Lucy's relative brain size is only marginally bigger than that of a chimp. We don't see marked expansion until possibly Homo rudolfensis, and definitely Homo erectus. So yes, bipedalism came long before a significant increase in encephalization.

    Molecular, 1.7 mya is pushing it for the oldest Homo erectus finds, which are estimated at 1.55 mya - definitely suggests that perhaps the gene you mentioned was associated with encephalization.
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    Quote Originally Posted by paralith
    Lucy's relative brain size is only marginally bigger than that of a chimp. We don't see marked expansion until possibly Homo rudolfensis, and definitely Homo erectus. So yes, bipedalism came long before a significant increase in encephalization.

    Molecular, 1.7 mya is pushing it for the oldest Homo erectus finds, which are estimated at 1.55 mya - definitely suggests that perhaps the gene you mentioned was associated with encephalization.
    I think I was getting muddled. I did mean that it correlated with encephalization not bipedalism!
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    What about hunting tools? An animal that can run faster standing up than the next would have a better chance of killing a difficult prey that requires the use of a spear or something. Do we have an idea of what kind of larger prey might have been around in the forest at that time? Maybe hogs?
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    At the time bipedalism was developing I think protohumans were more often prey than hunter. Probably scavengers when they ate meat. (Tasty brains easier to get to with long spindly fingers).
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    As I just did a paper last semester on the possible diet of Australopithecus afarensis, I can tell you it is unlikely (based on current evidence which is of course not the greatest) that they ate meat in any significant amount. Mostly small soft fruits, fresh shoots and leaves, possibly some tubers. This is all based on microwear and tooth morphology, sadly no isotope work has been done on this species (which would tell us relative proportions of C3 versus C4 plant foods they ate).
    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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    Quote Originally Posted by KALSTER
    What about hunting tools...run faster standing up
    It's a common sense solution but, looking at our modern relatives: they run best while carrying an object by adopting less upright posture than their casual posture, running three-legged. They push off with hind legs while pivoting on one arm, or both arms if it's a durable object (not a baby!).

    Quote Originally Posted by Numsgil
    At the time bipedalism was developing I think protohumans were more often prey than hunter.
    In a group, alert hominids only suffer freak predation. We adopt an intimidating posture, swinging and throwing objects, hooting, fainting and outflanking. We humans still do this instinctively. AFAIK only (arboreal) orangutans lost it. Predators learn we're not worth the hassle. They rather prey that flees, they can single out with impunity.

    Quote Originally Posted by paralith
    unlikely that they ate meat in any significant amount. Mostly small soft fruits, fresh shoots and leaves, possibly some tubers.
    So we wanted to drive competing herbivores away from food sources, and better yet have them keep well away while we foraged a choice area in peace.
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    Quote Originally Posted by Pong
    Quote Originally Posted by KALSTER
    What about hunting tools...run faster standing up
    It's a common sense solution but, looking at our modern relatives: they run best while carrying an object by adopting less upright posture than their casual posture, running three-legged. They push off with hind legs while pivoting on one arm, or both arms if it's a durable object (not a baby!).
    This point is debatable, but it's also important to keep in mind that running is a significantly different form of locomotion than walking, and given the compromise morphology of the first bipeds, running bipedally may have been highly impractical. I'm not sure though, I've never read anything on running estimates for Lucy and her ilk, only walking. Also, it's likely that at the time of Lucy infants were still able to cling to their mothers, especially given that Lucy was probably still partially arboreal herself.

    Quote Originally Posted by Numsgil
    At the time bipedalism was developing I think protohumans were more often prey than hunter.
    In a group, alert hominids only suffer freak predation. We adopt an intimidating posture, swinging and throwing objects, hooting, fainting and outflanking. We humans still do this instinctively. AFAIK only (arboreal) orangutans lost it. Predators learn we're not worth the hassle. They rather prey that flees, they can single out with impunity.
    Estimating predation rates on primates in general is notoriously difficult. It happens so rarely when humans are around to observe it. More often individuals simply go missing and there's no way to be sure what happened to them. Some also question whether or not great apes are significantly predated upon simply by virtue of their body size; and yet, others say that orangutans are probably almost completely arboreal because of predation (though those predators may very well have been humans). The behaviors you describe, Pong, are used in intimidating each other, and yes, male orangs will to intimidate one another on their occasional encounters. To my knowledge no one has ever observed this type of behavior in response to the presence of a predator.

    Quote Originally Posted by paralith
    unlikely that they ate meat in any significant amount. Mostly small soft fruits, fresh shoots and leaves, possibly some tubers.
    So we wanted to drive competing herbivores away from food sources, and better yet have them keep well away while we foraged a choice area in peace.
    An interesting idea, but evolutionary history seems to suggest that response to this type of competition is movement towards a new niche. It has been suggested, though I'm unfamiliar with what the evidence on this is, that our ancestors were in fact driven to the undesirable jungle edges by the better jungle-adapted chimpanzee ancestors. Thus we responded by adapting to this new niche.
    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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    http://www.jstor.org/pss/1469413

    http://johnhawks.net/weblog/reviews/...opes_2005.html

    I found these two interesting pages.

    Adaptations generally, as I have it, are usually ones that would help the animals survive trying times, whether it is food scarcity or abundance of predators, etc. I am thinking that early Hominines would have preferred to expend as little as possible energy while food was abundant (and inert or easy to catch), but when a dry spell happened they would have worked harder for food. I am thinking that this could have been where a faster running hominine with a spear would have had a better chance of surviving.

    One of the possibilities that fit the isotope evidence in A. africanus and A. robustus suggested by the second link includes an intermittent diet of grazers, animals that eat high C<sub>4</sub> plants. Being able to run at a fast pace while wielding a spear would have made it that much easier to catch them. A diet that includes termites might have accounted for some of the high <sup>13</sup>C levels present in their tooth enamel, but that would have required it to make up 40% of the diet, which apparently is not likely. They could also have hunted leaf eaters, but these would not have contributed to <sup>13</sup>C content, so could be hidden in the results.

    How wrong am I?
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    Your information is accurate as far as I know, you just have to remember that africanus and robustus came on the scene after bipedalism first appeared. They're not necessarily the best models for understanding why bipedalism is adaptvie.
    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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    Quote Originally Posted by paralith
    Your information is accurate as far as I know, you just have to remember that africanus and robustus came on the scene after bipedalism first appeared. They're not necessarily the best models for understanding why bipedalism is adaptvie.
    Those afarensis isotope studies would then be very interesting, as you said.
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    Quote Originally Posted by paralith
    Quote Originally Posted by Pong
    running three-legged
    This point is debatable... compromise morphology... Also, it's likely that at the time of Lucy infants were still able to cling to their mothers
    Yeah I can see the compromising path to full bipedalism. How does the mechanical problem of toting babies around fit this puzzle? Or maybe solve it?

    I've thought that retaining a stick - a walking stick! - might have been literal crutch along part of our evolutionary path. It's a safe bet we already had an eye for "a good stick" and employed various sticks in normal activity. So what happens if pedally-compromised Lucy holds onto her good stick, and wants to cross open ground with it? Maybe we'd see that in the wrist bones?

    Quote Originally Posted by paralith
    Quote Originally Posted by Pong
    Quote Originally Posted by paralith
    unlikely that they ate meat in any significant amount. Mostly small soft fruits, fresh shoots and leaves, possibly some tubers.
    So we wanted to drive competing herbivores away from food sources, and better yet have them keep well away while we foraged a choice area in peace.
    An interesting idea, but evolutionary history seems to suggest that response to this type of competition is movement towards a new niche.
    While it's true that swans, geese, and ducks specialize in different corners of overlapping niches, and we could surely prove it by their fossils, we know practically all herbivores and omnivores compete daily for the same food sources. I think it's safe to assume we faced competition! So whatever we could do to drive off other species must have been advantageous, especially if we didn't hunt. Are you suggesting Lucy slunk away from birds and monkeys?

    Quote Originally Posted by paralith
    The behaviors you describe, Pong, are used in intimidating each other
    And other species, no wiggle about it. These behaviours (standing, swinging arms & sticks, throwing objects, yelling) are vital to the survival of hominids on the ground, at least when facing a predator. Watch Chimps Attacking Leopard.

    Moreover the efficacy of those behaviours against animals is easily proved by modern humans scaring off any old animal we meet in our yards or in the bush. It works. We do it instinctively. Why would modern city-dwellers hold effective instincts regarding other species and not have those earlier?

    BTW advice to hikers for surviving bear attack is stand your ground, make noise, raise your arms high. Flight makes the animal think you're prey.
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    At what point did human ancestors begin to lose body hair? I believe the current mode of thought by experts is that it occurred as a result of better cooling. Did it occur at the same time bipedalism began to form?
    "The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt" - Bertrand Russell
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    I apologise if I am going off topic slightly. This is all I have left to contribute

    In various articles Booth et al. suggest that it was not unusual for members of the hunter-gatherer society in the Late Paleolithic (50,000-10,000 BC) to undergo feast (during food abundance) and famine cycles (under drought conditions, unsuccessful hunt or inability to hunt due to physical inactivity or illness). Survival during starvation depends on the amount of fat stored. The record for surviving starvation is 382 days (Stewart and Fleming 1973).

    Neel (1962) proposed the ‘thrifty genotype’ hypothesis. It proposed that genes allowing the conservation of energy storage aid survival during subsequent famines. The thrifty genes that are beneficial for surviving starvation become deleterious in sedentary societies with abundant food because the deleterious phenotype is exposed well after sexual maturation.

    Prolonged periods of physical activity (foraging, hunting) and rest were also part of the lifestyle in the Late-Paleolithic era. It is estimated that men hunted 1-4 non-consecutive days per week and women have gathered food every 2-3 days.

    Chakravarthy and Booth (2004) therefore extend Neel’s (1962) ‘thrifty gene hypothesis’ and state that human beings were also selected for genes that support a physical activity-rest cycle.

    A lack of famine and physical activity as we see today leads to the development of chronic disease. We are living a space age lifestyle with a genome selected for a stone age life which results in chronic diseases such as heart disease, diabetes and hypertension among others.
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    That's fairly topical if it means we developed posture under the condition of fat and slim seasons. And just look at those paleolithic Venus figurines. On all fours she'd be snagging nipples, and crushing the the baby clinging to her tummy too.

    Just how could our female ancestors move anywhere with pregnant belly and breasts heavy with nursing a first child she's got to carry? And then make her fat on top of that?

    I know we can guess weight by shin bone. But what if heavy-boned folk like neanderthals were really adapted to seasonal obesity, straining their bones during a sedentary glutted period... like, eating ten mammoth.
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    Ok, so the possibility exists that bipedalism was beneficial in terms of more efficient hunting during difficult times.

    Now, would a bipedal stance be beneficial when fighting for position within a group? Chimps fight with fists much as we do, so being able to hold your balance while manoeuvring about while exchanging blows could be a serious advantage. The same goes for when territory disputes arise. Being able to wield a weapon during all of this would also have been advantageous, no?

    What type of trees where prevalent during those times? Could they have been able to better hold their balance when traversing a long solitary branch if they could walk upright more efficiently? This could have helped with reaching difficult to reach fruits or escaping an attack or when doing the attacking.
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    I think we evolved bipedalism because we were tired of looking at assholes.

    Unfortunately this didn't quite work out the way it was intended, since whole people turned into assholes when our brain size increased.
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    Quote Originally Posted by spuriousmonkey
    I think we evolved bipedalism because we were tired of looking at assholes.

    Unfortunately this didn't quite work out the way it was intended, since whole people turned into assholes when our brain size increased.
    Speaking of which...

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    Yes, I do have a large brain.
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    Quote Originally Posted by KALSTER
    Now, would a bipedal stance be beneficial when fighting for position within a group?
    Apparently it is, but patriarchal advantage doesn't apply to females. Men are no more graceful on their feet than women.
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    Quote Originally Posted by Pong
    Quote Originally Posted by KALSTER
    Now, would a bipedal stance be beneficial when fighting for position within a group?
    Apparently it is, but patriarchal advantage doesn't apply to females. Men are no more graceful on their feet than women.
    Does that say anything though? A male that can fight better by being better at bipedalism and gain higher status, would produce more offspring with better bipedalism of both sexes. That female offspring would then in turn stand a higher chance of producing offspring with better bipedalism, who then go on to gain higher status, etc...
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    If so then gorilla girls would grow up to be silverbacks.
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    Quote Originally Posted by Pong
    If so then gorilla girls would grow up to be silverbacks.
    That is just gene expression though isn't it? Reaction to hormones? Is there any reason why the mutation has to be bound to sex? What if the females can also gain from being able to walk better, or just having longer legs even.
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    :? I get what you're saying. Multiple, sex-specific pressures apply to this "single" adaptation. Third opinion, anyone?
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    It depends on the cost to female. In general females try to avoid direct physical conflict because any injury they suffer could seriously affect their ability to care for any dependent offspring, now or maybe even in the future. This isn't to say females won't be aggressive but they go about it differently; a female won't posture and signal and warn that she is about to attack - she waits until your back is turned and hits you hard. I was just told an anecdote today about chimps raised with humans, where a female nearly ripped out the jugular of a carer who had harrassed her some weeks previously - she was out walking with a different caretaker, saw the harrasser, and made a beeline for him from behind.
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    Or more recently the incident of a 4 legged 'house' chimp, ripping off the face of one the bipedal housemates.

    The answer isn't going to be found by looking at some general beneficial function of bipedalism.

    Evolution of adaptations such as this one is usually caused because of fall-back adaptations.

    For instance, a certain species has teeth adapted to eat nuts. Ironically they don't eat nuts most of the time. Why are their teeth adapted to eating nuts? Because during a short period in a year there is nothing to eat but nuts, and if they don't eat nuts they will die or be severely affected in their ability to compete.

    That's a fall back food.

    I venture to guess something similar happened to bipedalism. It didn't evolve for the things it later became good at. It had a more important function that was used only once in a while, but it was critical.
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  41. #40  
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    Quote Originally Posted by spuriousmonkey
    I venture to guess something similar happened to bipedalism. It didn't evolve for the things it later became good at. It had a more important function that was used only once in a while, but it was critical.
    What then? The setting is forest fringes. So we're migrating between groves of depleteable resource, I think, and the dodgy part is the grassy expanse between groves. In that journey I imagine we'd be vulnerable, terrified, conspicuous, but resolved to press on despite savanna predators like pack baboons shadowing us at opportunity range.

    Wouldn't we along that whole gauntlet maintain the standard "intimidate predator" behaviour? That is: walking upright, hooting, swinging sticks. Wouldn't it work better than any other strategy? The reward is every isolated "island" of forest too small to support permanent forager population. Real treasure there.

    If it worked passably well, we'd not only refine it, but other species would adapt to avoid it. Then we'd begin to own the savanna as well.



    I'm depending on assumption that how chimps and humans behave in common today is how our ancestor also behaved.


    EDIT:
    Out in the middle of nowhere, it would be a really good idea not to drop the stick. Something about the size of staff or cane is ideal. If employed as walking support (I know I'm getting weird now) the fossils should reflect that. Specifically, the wrist would be unusually sturdy for non-arboreal hominid, and the hand perhaps rotated to best grasp a vertical staff, or in the case of shorter stick (cane) the carpal tendons would be strengthened.
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  42. #41  
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    Quote Originally Posted by Pong
    What then?
    Something that isn't obvious.

    So no point in looking for sensible obvious routes.

    The only thing you can be sure of is that the behaviour, adaptation was essential.

    But that doesn't mean that it has to be a central feature of what we conceive is a human being.

    It is probably something that left no trace.
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    I just learned that gorillas use walking sticks. A female was observed employing stick to balance bipedally (tripedally) and gauge water depth while fording waist-deep, and also planting stick to lean on while scooping plants near water's edge.

    I think we can assume our ancestors employed walking sticks sometimes, and hypothesize this tool supported our development. Does anybody know the fossils well enough to corroborate or refute habitual use of walking stick? I'm predicting an arm and wrist optimized for prolonged leaning on a staff or top of cane, as we see humans do today.

    Another way to approach the question, is to ask why prehistoric and historic humans widely depended on staffs ("What walks on four legs, then two legs, then three legs?") if they didn't earlier. Our balance and stamina on two legs is supposed to be improving. If Lucy didn't need a staff but Boy Scouts do, she must be ahead of her time and ours!
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