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    Food - The Key To Human Bipedalism?
    By Catarina Amorim | April 20th 2012 07:16 AM | 19 comments | Print | E-mail | Track Comments
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    After many years as a scientist (immunology) at Oxford University I moved into scientific journalism and public understanding of science. I am...

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     Our ancestors might have started walking on two feet in order to carry food more efficiently suggests new research in the journal Current Biology.

    Bipedalism (walking on two feet) is one of the key features that distinguishes us from chimpanzees and gorillas, our closest relatives, but it is also an adaptation that radically changed our evolution when it released our ancestors’ hands to all kind of jobs.

    Despite its importance, the reason why the behavior first appeared remains a mystery. But now a study by researchers from Portugal, the UK and Japan, using wild chimpanzees as a proxy model for early hominids, discovered that limited availability of highly desired foods turns the animals bipedal in order to be able to carry more items quicker. Since the circumstances where bipedalism occurs among chimpanzees probably parallel the challenges faced by first hominids, the results suggest that a need to collect and carry food was crucial in the evolution of the upright posture among hominids.

    Walking on two feet was a dramatic step in the transition from ape to man. Releasing the hands to make tools and hold weapons or infants led to new ways of feeding and living, as well as the challenges that contributed to the human lineage’s bigger brain. The first signs of bipedalism coincide with a time of major climate changes that reduced forested areas around 5 millions of years ago, and with the first hominids. In fact, Australopithecus 3.6 millions years ago already had physiological changes linked to an upright posture, such as spinal adaptations for vertical pregnancies in females and modified bones in the feet and legs.

    But even if environmental changes are linked to the appearance of bipedality among hominids the specific issues/selective pressures that trigger it remain a mystery.

    To test one of the main theories on the subject - which proposes that walking upright appeared from a need to free the arms to carry food - researchers Susana Carvalho, Dona Biro and colleagues from the University of Coimbra in Portugal and Oxford and Cambridge Universities in the UK in the study now published studied wild chimpanzees from the forest of Bossou, in Guinea as a proxy model for early hominids. Not only chimpanzees are often bipedal, but those in Bossou, similar to early hominids,are facing an increasingly deforested habitat with highly variable ecological conditions.

    To start the researchers tested what would happen when a new nut, more appealing than those that the animals normally had access to, was introduced into their environment comparing three different situations – when the new nut was introduced in high quantities becoming the most common resource, when it was introduced in small amounts and, as control,when it was not present in the environment. 

    Observing more than 700 food transports Carvalho, Biro and colleagues found that when high quantities of the new nut were introduced chimpanzees not only stopped collecting other nuts but also did three times more food transports (presumably to collect as many new nuts as quickly as possible) showing that the new resource was particularly high-valued.

    Images and video courtesy of the journal "Current Biology"

     Even more interesting, in the presence of the new nut, food transports were five times more frequently bipedal probably because this allowed chimpanzees to carry twice as many items than when walking on all four limbs. 

    These results reveal how upright locomotion among chimpanzees can appear from a need to improve food carrying efficiency when resources are scarce or unpredictable, suggesting that the same might have occurred among the early hominids.

    To further confirm this possibility Carvalho and Biro next investigated another situation where access to high-valued food was unpredictable - when chimpanzees raided human plantations. Again more than a third of the transports were bipedal with the animals using both their mouth and hands in order to carry many more items.

    These are particularly interesting results because bipedality among chimpanzees is usually postural, so not for locomotion, and used to have access to fruit in short trees, not to carry items. The foraging behavior of the Bossou’s chimpanzees - who live in an area where forest has been reduced and replaced by patches of other vegetations or even human plantations – give us with clues on what might have happened during hominid evolution when the ecological conditions were also changing rapidly. If the environment of early hominids also had high value unpredictable resources(maybe as result of the changing climate of the time), then it would have been advantageous to turn bipedal as this allowed individuals to carry and collect more resources quicker increasing their survival chances. And if bipedalism was  used often, with time the anatomic changes that facilitated an upright posturewould have been selected and incorporated into the hominids’ populations.

    In conclusion, the work now published supports the theory that hominids started to walk upright to be more efficient when carrying food, which could have become scarcer and more unpredictable with the changes in climate (and vegetation) that occurred at the time of the first hominids. Standing upright, by allowing them to carry and collect high-value resources quicker, improved survival chances. 

    The results also support the idea that highly variable environments (more than specific habitats) were behind important adaptive evolutionary steps in the history of humans.

    Citation: "Chimpanzee carrying behaviour and the origins of human bipedality”, Current Biology,Volume 22, Issue 6, R180-R181, 20 March 2012 doi:10.1016/j.cub.2012.01.052

    Comments

    Gerhard Adam
    While it seems that this is certainly an element of what probably occurred, it seems that other even more important elements are missing [or were not addressed].

    The most obvious question is "why carry food at all"?  This would suggest that the driving forces were actually increased cooperation, social interdependence, and having a "nest" or a fixed place in which they lived.  This is a point addressed by Edward O. Wilson in his new book "The Social Conquest of Earth".

    Mundus vult decipi
    amorca
    I would think that it's actually more to collect resources to oneself Gerhard - they also carry tools/stones to break the nuts and if you see the video the chimp collects the food and moves away from the others to apparently  eat
    Gerhard Adam
    I honestly think that would be of limited utility.  After all, one can't acquire very much additional food [beyond that which you can readily eat] since to do so would require a means of being able to protect what you've acquired.  So, while I'm not disputing the fact that they may take food and go off by themselves to eat it, it just doesn't seem like much of an advantage nor selection pressure.

    In viewing the video, your conclusion doesn't seem warranted.  In fact, it doesn't look much different than the way a human might behave at a picnic.  Take some food, and find a comfortable place to sit down and eat it.  In other words, the chimp didn't actually move away from the group [at least not in any appreciable sense].  In addition, you could see the others also sitting there, apparently without any sense that they were competing for the nuts. 

    Actually in watching the video more closely, it appears that the exactly opposite is happening from what is being described.  The chimp appeared to move closer to the group and not farther away.  He was much more isolated in his original position [just estimating based on the number of steps he took to get to the group where the stones were].  Once he sits down, you can now see others from his group, so it seems he's moved closer, not farther away.
    Mundus vult decipi
    Thor Russell
    According to this article about "The Social Conquest of Earth"http://online.wsj.com/article/SB10001424052702303404704577311553569846904.html


    "It's not every book that is preceded by a critical public letter from more than 130 of the author's peers, as Mr. Wilson's was when a legion of biologists wrote to the journal Nature last year to register their belief that his current thinking is wrong."


    If this claim is correct, (I'm no wsj fan) would you care to provide a link to such a letter (I can't find it) in the interests of balance and so readers can be more informed about why they object in such a way?
    Thor Russell
    Gerhard Adam
    This kind of encapsulates the debate.

    http://news.sciencemag.org/scienceinsider/2011/03/researchers-challenge-eo-wilson.html

    However, despite all the bravado, the reality is that kin selection has never actually made much sense, since the primary criteria of assisting kin is dependent on being able to actually recognize them.  After all, without that little tidbit, the theory is conflating proximity with kinship [in other words, it's more important who you were raised with, than actually knowing if you're genetically related].

    In addition, inclusive fitness is attempting to explain the eusociality of insects [ants/bees] despite the fact that the claims don't hold up in practice.  It's all well and good to proclaim that the members of a colony cooperate because they all share the same genes, but that isn't necessarily true [such as when a queen bee is replaced in a functioning hive].

    In addition, there have been papers that demonstrate that many ant colonies are not closely related, genetically and this is especially true of the Argentinian fire ants that form super-colonies between different queens and unrelated members.

    So, while the main thrust still favors Hamilton's rule, the reality is that it almost never fits where it is actually applied.  One of the most famous quotes comes from Haldane.
    He famously said that, "I would lay down my life for two brothers or eight cousins"
    With just a little scrutiny, one can see the sleight of hand in this comment.  In other words, Hamilton's rule holds ONLY if he can save two brothers or eight cousins at the same time.  In any other circumstance, it wouldn't apply.  More to the point, even if the circumstances were as described by Haldane, the only logical conclusion is to simply let them die, because the best odds for passing your genes on, is to not risk your life saving any of that lot.
    "It's not every book that is preceded by a critical public letter from more than 130 of the author's peers, as Mr. Wilson's was when a legion of biologists wrote to the journal Nature last year to register their belief that his current thinking is wrong."
    Let's also bear in mind that 130 authors or 130,000 authors is still just an argument from authority and doesn't constitute evidence.  What I find more interesting is that Wilson clearly has enough "clout" to raise such hackles.  Yet, when you read the criticisms, they are fairly weak refutations of Wilson.

    My critique of one of the original studies for kin selection is located here and it illustrates how poorly the data actually match up.
    http://www.science20.com/gerhard_adam/hamiltons_rule_again
    Mundus vult decipi
    amorca
    This is what the paper say Gerhard
    Chimpanzees carried food-items and food-related objects (tools), when the latter were needed to process the food. Simultaneously carrying nuts and tools to another location may have energetic advantages — such transports may help individuals to establish temporary ‘personal space boundaries’, or ‘exclusion zones’, allowing them to consume more and share less, especially at higher levels of group competition. 


    For chimpanzees, whose activity budgets comprise little overall daily locomotion [10], such carrying of valuable items could act as a strong selection pressure. The energetic intake resulting from resource monopolizing through short bipedal bouts of carrying may eventually select for a gradual anatomical change. We predict that if the environment of early hominins provided similar high-value, unpredictable resources at a greater frequency than seen in most of today's chimpanzees, this could reward higher frequencies and/or longer distances of bipedal bouts of carriage, creating a selection pressure for more economical bipedality. 

    Steve Davis
    Gerhard, there might be slight weaknesses in the video, but I think the overall conclusion is correct.
    Indigenous Australians for example, carried both food and water over significant distances in dry savannah and desert regions as resources in one area depleted.
    It seems to be generally accepted that climate change was the trigger for bipedalism, and I think the carrying of food and water would have been a manifestation of that. 
    Gerhard Adam
    I want to be clear.  I'm not disputing the value of carrying food or tools.  My only point of contention was that this [the carrying of food and tools] made much more sense in light of a tighter social organization and having a "nest" or base to return to. 

    Regardless of the video's strengths or weaknesses.  It is completely unconvincing that this was anything other than a social group congregated together for a meal.  There wasn't the slightest indication that individuals were separating themselves to create boundaries or avoid sharing.  After all, sharing isn't always necessary, so there's no reason to believe that it is present in every situation and every meal.  It is equally interesting to note that none of the other chimps seems to give the slightest notice to the one carrying the nuts or picking up stones.  This isn't actually very convincing as being a "high competition" scenario.  Whether this is a problem in what was recorded or not, the video simply doesn't illustrate what is being claimed by the authors.

    On the other hand, if the video showed a group traveling together and then specifically taking their share and isolating themselves, then it may be more convincing.  However, I suspect that such a scenario almost never occurs, because it would leave the chimpanzees open for predation.

    Most animals tend to eat where they happen to be, so that even in the case of predators, transporting food is largely to protect the kill or move it to a more secure location.  To the best of my knowledge the animals that carry food [significantly transport] invariably do so because they have a "nest" or a permanent/semi-permanent residence. 

    As I said, my point of contention is not in the transportation of food/tools, but rather in the interpretation that it is intended to provide a means whereby animals could isolate themselves to avoid sharing.
    Mundus vult decipi
    Steve Davis
    "...my point of contention is not in the transportation of food/tools, but rather in the interpretation that it is intended to provide a means whereby animals could isolate themselves to avoid sharing."
    If that's the interpretation then I'm with you. But I have to say that I did not read it that way.
    Gerhard Adam
    That interpretation is based on the author's assumptions regarding the importance of food carrying in high competition situations. 
    ...such transports may help individuals to establish temporary ‘personal space boundaries’, or ‘exclusion zones’, allowing them to consume more and share less, especially at higher levels of group competition.

    More efficient access to resources may be crucial given this uncertainty (i.e., ‘If I return later, will any resource be left?’).
    http://www.cell.com/current-biology/fulltext/S0960-9822%2812%2900082-6?large_figure=true
    The last statement especially begs the question regarding "why leave in the first place?"  This isn't exactly a novel problem unique to primates.  All animals face such choices, and for most there is no compelling reason to leave their food, unless specifically threatened or driven off. 

    However, another telling part of this, is that it only occurs because of the supposed behavior within the group, itself.  Clearly carrying food like this, is not postulated to have any bearing on the group's security or to avoid other threats. 

    As I result, I find it less than compelling to believe that internal group competition was a sufficient selection pressure for bipedal development.  This would have worked counter to the evolution and strengthening of social bonds and structures.  In which case, the ability to carry would have been irrelevant.  If anything, the evolutionary trajectory of social cohesion would argue that carrying behaviors became more important to transport food back to the group and to promote sharing.
    Mundus vult decipi
    Steve Davis
     "I find it less than compelling to believe that internal group competition was a sufficient selection pressure for bipedal development."
    Gerhard, I'm with you all the way.
    "...allowing them to consume more and share less,..."
    It's comments like that which show the pervasiveness of selfish gene theory.
    Researchers trot out unsubstantiated comments like that without a second thought, secure in the knowledge that they have parroted the current orthodoxy.
    Gerhard Adam
    Well, I want to be clear that I'm not naive about the nature and even violence of competition between primates and their various groups.  However, it is equally clear that much of the more extreme violence occurs between groups, which still requires a strong social connection between those members in any particular group.

    As a result, there's no doubt that carrying food, tools, and weapons is an important adaptation, but I'm simply not convinced that it evolved as a result of competition within a group.  That seems to be the least plausible explanation, whereas if one considers the ability to carry items from raids on other groups back to one's own territory, the picture becomes a bit more likely.
    Mundus vult decipi
    Bonny Bonobo alias Brat
    Bipedalism (walking on two feet) is one of the key features that distinguishes us from chimpanzees and gorillas, our closest relatives, but it is also an adaptation that radically changed our evolution when it released our ancestors’ hands to all kind of jobs.

    Despite its importance, the reason why the behavior first appeared remains a mystery. But now a study by researchers from Portugal, the UK and Japan, using wild chimpanzees as a proxy model for early hominids, discovered that limited availability of highly desired foods turns the animals bipedal in order to be able to carry more items quicker....Walking on two feet was a dramatic step in the transition from ape to man. Releasing the hands to make tools and hold weapons or infants led to new ways of feeding and living, as well as the challenges that contributed to the human lineage’s bigger brain.
    This video also shows a chimp doing a good impression of very competent bipedalism or walking on two feet and then wielding a weapon. Are we really sure that bipedalism is one of the key features that distinguishes us from chimpanzees?
    My latest forum article 'Australian Researchers Discover Potential Blue Green Algae Cause & Treatment of Motor Neuron Disease (MND)&(ALS)' Parkinsons's and Alzheimer's can be found at http://www.science20.com/forums/medicine
    Steve Davis
    "Are we really sure that bipedalism is one of the key features that distinguishes us from chimpanzees?"
    Certainly, because in chimps it is occasional, in humans it's universal.
    Gerhard Adam
    ... and after too many drinks, it is easy to see some humans partially reverting back to their chimpanzee quadrupedal manner of walking. 
    Mundus vult decipi
    Bonny Bonobo alias Brat
    "Are we really sure that bipedalism is one of the key features that distinguishes us from chimpanzees?"
    Certainly, because in chimps it is occasional, in humans it's universal. 
    Yes Steve its occasional for chimps, bonobos and gorillas and universal for us, but as the following videos show, some gorillas and bonobos are very adept at walking, running, dancing, twirling and standing upright whenever they choose to, so I personally don't see it as a very key feature that 'distinguishes' us from them. Especially as one of the videos shows gorillas running upright and possibly faster than our fastest humans.This video shows bonobos walking upright gathering food and is also rather nice demonstration of an alpha female asserting herself in the bonobo matriarchy

    This video shows 2 gorillas who are both very adept at running and who would probably in my opinion easily beat a man in the 100 metres Olympics sprint.

    This lovely video shows a baby bonobo walking upright while playing at wearing clothes

     And last but not least, this video shows a young female gorilla walking upright wading, twirling and dancing in water.


    My latest forum article 'Australian Researchers Discover Potential Blue Green Algae Cause & Treatment of Motor Neuron Disease (MND)&(ALS)' Parkinsons's and Alzheimer's can be found at http://www.science20.com/forums/medicine
    Thor Russell
    Yes it does seem that walking upright may not be the key to why we are human. If bonobos, gorillas etc can do it to some extent, then I don't see why it would be such a significant evolutionary event for it to become more common. I think something to do with language/abstract thought/communication and a theory of mind was what caused the rapid changes, and accelerated use of technology though teasing out cause and effect is always going to be difficult. I do think that adapting to an extremely difficult and changing environment is part of the reason, requiring intelligent cooperation/planning etc. If the changes are too rapid and varied to allow genetic/physiological changes, then its either get smart or die. 
    Thor Russell
    Gerhard Adam
    Actually it is a key feature, although [obviously] not the only one.  You seemed to focus on the speed, but it isn't speed that is relevant.  Humans are long distance runners and because they can travel long distances carrying things [especially weapons] is one of the things that made them particular formidable hunters.

    They couldn't outrun the animal, but they could wear it down [especially if injured] because they could run for much longer periods of time.

    Also, it isn't just a matter of whether an animal can be bipedal.  Hell, I've got a dog that can do some of that stuff too.  However, even in watching the gorilla run, you can see that the arm movements are awkward, so it isn't the most common method of locomotion or even standing.  You can easily see that even the shape of the back isn't particularly suitable for long-term bipedal movement or activity.  So, it isn't that they can't do it, it just isn't as fundamental to them as it is to humans.  Humans are the exact opposite.  Moving on all fours is awkward for humans.
    Mundus vult decipi
    Steve Davis
    There's probably little doubt that a significant transition such as bipedalism would need more than one or two factors.
    I think Thor's point about abstract thought is a good one.
    Apes will walk upright because they can. Humans walk upright because they want to, and that is due to many things, all associated with abstract thought, language etc.