When Did Bipedal Locomotion Begin?

National Geographic and New Scientist are both reporting on a new study, in the journal Science, that provides an interesting angle on the question. The study is the result of over 3,000 observations on orangutan behavior in Sumatra (from New Scientist):

Thorpe spent a year recording orang-utan behaviour in the Gunung Leuser National Park in Sumatra, Indonesia, and from nearly 3000 observations of locomotion, the team concluded that the apes were more likely to walk on two legs – using their hands to guide them – when they are on the thinnest branches, less than 4 centimetres in diameter.
On medium-sized branches – those greater than 4 cm but less than 20 cm diameter – the apes tended to walk bipedally, but used their arms to support their weight by swinging or hanging.
Only on the largest branches, with a diameter greater than 20 cm diameter, did the animals walk on all fours.

This leads researchers to suggest:

“Walking upright and balancing themselves by holding branches with their hands is an effective way of moving on smaller branches,” says Robin Crompton of the University of Liverpool, UK, who was also involved in the study.
“It helps to explain how early human ancestors learnt to walk upright while living in the trees, and how they would have used this way of moving when they left the trees for a life on the ground.”
So, rather than evolving to walk on two feet after scrabbling around on the floor on all fours, the theory suggests our ancestors already had the rudimentary means of walking on two feet before they even left the trees.
When the ancestors of chimps and gorillas left the trees, however, they needed to maintain the ability to climb tree trunks. This need for tree-climbing strength and anatomy guided their evolution at the expense of more efficient terrestrial movement, and therefore led to knuckle-walking, says Crompton.

One interesting thing to note is the differing opinions of the outside experts National Geographic and New Scientist consulted on the story. National Geographic went with Brian Richmond who says:

“This is interesting and a very good study of how orangutans climb and walk in trees, but it’s not a study of our distant ancestors,” he cautioned.
“It tells us something about how primates other than ourselves use bipedalism. That could tell us something about how bipedalism might have been used by our distant ancestors. But it doesn’t tell us what actually happened,” Richmond said.
“It doesn’t show us the origins of our own human bipedalism.”

I kind of agree. Certainly, the research does not prove how bipedalism originated, but it does throw some interesting light on the question and gives us new ideas about what led to bipedalism. In that sense, the study is highly valuable (I’m working on tracking down a copy and will probably have more to say later).
New Scientists went with Chris Stringer and Paul O’Higgins (who was also was consulted by National Geographic):

“Nevertheless, this is the best observational data on the importance of hand-assisted bipedalism to orangs, and its possible implications for the evolution of human bipedalism.”
Since all the sites which have yielded fossil evidence of our earliest ancestors were forested or wooded, rather than open, Stringer says, “arboreal bipedalism is certainly a very plausible mechanism for the origins of walking upright.”

O’Higgins mentioned a point mirrored by Richmond:

“If extended hip and knee bipedalism did indeed arise in the distant past, this makes the task of identifying possible ancestors of the human line much more difficult,” he says.

Richmond said something pretty similar as well, but I don’t think this is a new problem, because most paleoanthropologists would expect that the closer we get to the LCA between us and chimps the harder it will be to tell them apart…
Update 1: Kambiz has an interesting discussion of the subject also.

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6 Responses

  1. I have the full text(pdf) of the article, so if your other methods fail you, I can email it to you.

  2. Chris – Thank you for the offer, but I have a copy now.

  3. Interesting and fascinating, but…1. where would you place the last common ancestor of humans and orangs and where geographically would that be? 2. what do you do with all those European Tertairy apes? Not all those environments were woody but none of the extreme oran adapations are present either 3. where does that put the “paranthropines”–do they represent a return to arboreality or its persistence?

  4. I had some stuff to say about this over at Internet Infidels, and since we’re painting the apratment today and I’m just about to start as soon as I finish my coffee, let me just cut and paste, since, hopefully, what I said is interesting (you never know — it could happen :)):
    One thing that people tend to forget about primates is that they virtually all use bipedalism at times. The general way sensible theorists look at hominid bipedalism is to show the number of activities during which apes use bipedalism, rather than one thing. For some reason, loads of people want to find one specific thing which does the deed all by itself when it was almost certainly a combination. Elaine Videan and William McGrew have done some experiments to see what some of the common ideas about bipedalism get you. Here’s the abstract:
    Videan EN, McGrew WC.
    Am J Phys Anthropol. 2002 Jun;118(2):184-90.
    “Bipedality in chimpanzee (Pan troglodytes) and bonobo (Pan paniscus): testing hypotheses on the evolution of bipedalism.”
    A host of ecological, anatomical, and physiological selective pressures are hypothesized to have played a role in the evolution of hominid bipedalism. A referential model, based on the chimpanzee (Pan troglodytes) and bonobo (Pan paniscus), was used to test through experimental manipulation four hypotheses on the evolution of hominid bipedalism. The introduction of food piles (Carry hypothesis) increased locomotor bipedality in both species. Neither the introduction of branches (Display hypothesis) nor the construction of visual barriers (Vigilance hypothesis) altered bipedality in either species. Introduction of raised foraging structures (Forage hypothesis) increased postural bipedality in chimpanzees. These experimental manipulations provided support for carrying of portable objects and foraging on elevated food-items as plausible mechanisms that shaped bipedalism in hominids.
    The idea that food-carrying was perhaps the biggest incentive among the various possibilities has been around a long time (as has the bipedal in trees idea, as has been pointed out here already). The one of their possibilities that Videan and McGrew felt might not have gotten a decent tryout in their tests is the one they call “Vigilance hypothesis”; they felt it was entirely likely they simply didn’t give their subjects something compelling to look at. Like a predator, for instance, which in a zoo setting can’t be made efective unless you want to loose some large predator in a chimp enclosure (which I think most zoo directors would frown on). As a last note, let me point out that the “aquatic ape” idea claims that water does it, and the idea’s proponents usually claim it’s either everything, the whole explanation, or the biggest one by far. Since apes and monkeys which wade usually do so quadrupedally this seems unlikely, but it would be on the overall list. But also it should be noted that bipedalism in water is most often when feeding or carrying, just as on land.
    EDIT: One other thing I meant to say before I got tangled up in posting that abstract and forgot was that all primates are essentially preadapted to bipedalism to some extent due to their posture. That is, the way the spinal column, head, and neck are situated means they don’t have to change much at that end of the backbone for bipedalism. This is because, well, A) virtually all do some bipedalism, as I mentioned before, and B) many are in an upright posture much of the time while climbing and moving in trees, plus C) when sitting and feeding or grooming, which for most is the majority of their waking hours, they tend to be sitting upright.

  5. QrazyQat – You wouldn’t happen to have a PDF of that article would you? It bears on some of the stuff in the Orang article – which is a little more complicated than the National Geographic, etc., article portrays it.
    Donald – This paper doesn’t affect the taxonomic status of any of the members of the superfamily Hominoidea. For question number 2, there are European Ramamorphs – ancestors of Orangs. For question 3, the Paranthropines (that is the robust australopithicines) would be looked at much the same way as Australopithecus afarensis

  6. No, I don’t. Wouldn’t mind getting one. I’m not surprised the paper is better than the news article. I’ve often complained about this sort of thing, and especially in the part that the researchers themselves and their university or foundation PR departments play in misdescribing the work — the reporters often get the blame, but I’ve seen before that it the confusion often starts with the PR dept, and sadly, the researchers (Wilson and “MtDNA ‘Eve’” was an example of that). It’s annoying, and I think destrcutive of science, since miscontrues how science happens (feeds right into creationist hands, among other problems like simply confusing laypeople about science).

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