Snapshot Serengeti Talk

bipedalism

  • Ettina by Ettina

    This may be a bit off-topic, but I had a thought about why we might be bipedal.

    See, predators such as lions need to know how big their prospective prey is. If it's too small, it's not worth the effort of catching. If it's too big, the probability of success gets lower, and the risk of injury goes up.

    If all your prey are quadrupeds, estimating size is probably pretty simple - just look at how tall they are. Most of the time, a bigger quadruped will also be taller.

    However, if you throw in a biped, they're going to be a lot taller for their size than a quadruped is. So comparing the size of a biped to the size of a quadruped is a lot more tricky. In fact, this sounds a lot like the Piagetian problem with the tall thin glass and the short fat glass.

    Now, there's no way lions are anywhere close to passing Piagetian conservation. So, does this mean they drastically overestimate the size of a standing human? And if so, could this be why we became bipedal in the first place?

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  • okopho by okopho

    Try a thought experiment: gather together a few healthy humans and several quadrupedal prey species of comparable size, and then introduce some hungry lions. What do you think the outcome would be? My guess is that if you ran the experiment a few times, you would see the same outcome over and over again. The quadrupeds would all run away really quickly, whilst the slow, puny, bipedal humans would be left behind to be eaten by the lions.

    It's simple thought experiments like this that have resulted in a huge number of competing hypotheses about the origin and evolution of human bipedalism. In a nutshell, the problem is this: how do you get any of the proposed advantages to balance out against all the obvious disadvantages? Needless to say, nobody has yet come up with a solution that is clearly better than all the others...

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  • Ettina by Ettina

    But why are we so slow and puny? We evolved in that environment, we must have had ways of surviving in it.

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  • davidbygott by davidbygott moderator

    The hominins would not be puny if they were organized and armed. There have been plenty of obs of baboon troops chasing away leopards and lions, and chimps ganging up to attack a leopard. If they make a lot of noise and throw things, that's even more effective. They can also climb trees to evade predators, and there's evidence that our ancestors could climb well even while they were becoming increasingly bipedal. I imagine that during the co-evolution of hominins and big cats, the big cats occasionally preyed on them but many times found it didn't pay off because the hominins were so aggressive or vengeful. You can't just view hominins in isolation as the slowest runners in the sprint event, you have also to consider their ability to cooperate, plan, deceive, and use weapons.
    That's my perspective based on a background of studying chimps and lions in the wild, as well as living among hunter-gatherers for years.

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  • okopho by okopho in response to Ettina's comment.

    Well, so much for the idea that bipedalism evolved in that environment, then!

    All the evidence shows that bipedalism evolved very early in our lineage - literally millions of years before the sophisticated tool use, big brains, culture, etc that we see amongst the later hominins. Also, it is important to realize that bipedalism evolved more than once amongst several groups of apes that lived around the same time as our early ancestors. And all these apes lived in a very different environment to the ones in which the later hominins did. In particular, the climate was much wetter and warmer then, which meant that Northern Africa and the Mediterranean Basin would have been covered in dense jungle.

    So bipedalism originally evolved amongst several lineages of arboreal apes 5-10 million years ago - not 3-4 million years ago on the savanahs of Eastern Africa. It is very important to keep in mind this distinction between the origin of bipedalism, and its subsequent evolution. Bipedalism in hominins has a very long and varied history.

    If we seem slow and puny compared with some of the animals that e.g. lions typically prey upon, this is a strong indication that our evolution was not primarily driven by those kinds of interaction. And as to the question of how we survived: many of the early hominins retained adaptions suited for living in trees long after they became bipedal. So if we ran my thought experiment with some Australopithecines, I would imagine that their first instinct would be to climb up the nearest tree, rather than try to outrun or intimidate the lions.

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  • davidbygott by davidbygott moderator

    Personally I love the aquatic-origins hypothesis (Alastair Hardy/Elaine Morgan) but alas, any circumstantial evidence for it would be deep under tropical seas 😃

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  • okopho by okopho in response to davidbygott's comment.

    Not sure if you were being entirely serious, but the various aquatic hypotheses have been pretty thoroughly debunked over the years - and in any case, no mainstream paleoanthropologist has ever taken any of them seriously.

    Having said that, the much simpler Wading Hypothesis has been given some serious attention, and does seem to have a lot going for it as an explanantion for upright posture/bipedalism.

    For anyone interested in reading a good, modern overview of the evolution of bipedalism, I would strongly recommend taking a look at this article. It's quite detailed (as you would expect from a scientific paper), but not too technical. The paper favours a Wading Hypothesis as the best explanation - but it discusses much more than that, and covers pretty much everything you could want to know on the subject of bipedalism.

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  • davidbygott by davidbygott moderator in response to okopho's comment.

    Just being provocative 😃 Exploiting the protein-rich littoral zone makes so much sense for a relatively unspecialized smart omnivore, and the wading hypothesis has a lot going for it. Thanks for that link, I shall enjoy reading it.

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