Standing up to fight, and human uniqueness

A new paper published in PLoS ONE by David Carrier tests the hypothesis that bipedalism in humans evolved because it helps them to fight better. The first fatal flaw lies in the first sentence:

Many quadrupedal animals stand on their hindlimbs to fight.

How then, does this explain human uniqueness?

Clifford Jolly wrote in The Seed Eaters,

“… it is illogical to invoke the behaviour of living apes to explain the origins of something that they themselves have not developed…”

and I think it would be great if we could ask ourselves why all of these bipedal aggression postures haven’t resulted in bipedal anteaters, felids, or canids, but were so important in human evolution. My dog does a cute little thing where she stands up on her hind legs to pounce a squeaky toy. Perhaps if I hadn’t had her spayed, her descendants would have been bipedal? (She also stands up to get food from low-hanging branches….er… coffee tables.)

A second flaw lies in their methodologies, in which they had humans stand bipedally to strike a force transducer, and then had them get down on their hands and knees and do the same thing.  What ancestral state does this posture approximate? Forget bent-knee, bent-hip- let’s go with knee-crawling! The authors themselves admit,

The fact that humans are habitual bipeds reduces the relevance of humans as a model organism for this study.

but add that using chimpanzees or bonobos would increase the “relevancy” of this particular experiment.  I don’t think it would. Chimpanzees and bonobos don’t represent an ancestral hominid, either.  You’d want to get a sample that included a bunch of different species- monkeys, anteaters, felids (why not?).  But I still don’t know that a protocol like that would support the hypothesis that humans evolved to be bipedal because that particular aggressive posture was important to their ability to secure a mate.

ResearchBlogging.org
Carrier, D. (2011). The Advantage of Standing Up to Fight and the Evolution of Habitual Bipedalism in Hominins PLoS ONE, 6 (5) DOI: 10.1371/journal.pone.0019630

About these ads

16 responses to “Standing up to fight, and human uniqueness

  1. Eric May 19, 2011 at 10:00 pm

    There are so many more interesting (and plausible) theories on the origin of human bipedalism, so why do people waste their time, effort and money on these kinds of studies?
    On the other hand, this study was even mentioned on a german newssite so at least the author gets some publicity.

    By the way, am I the only one who gets upset when he sees the aquatic ape theory being mentioned in a scientific paper?

  2. Mokele May 19, 2011 at 10:53 pm

    I have some reservations about Jolly’s argument, and also the first part of your criticism of this paper (though I agree with the second part).

    Any given species is a hodge-podge of traits under a wide variety of selective pressures, and if the species shows a mild version of a trait and uses it for a known function (not necessarily the only function), I would argue that it’s entirely possible that the expression of this trait is being limited by other constraints, and that removal of these constrains may allow the trait to reach a more “extreme” state. Inversely, when explaining an extreme trait, it’s acceptable to look at “less extreme” examples and their functions in nature for clues about it’s origins.

    After all, while it’s not primates, orthograde terrestrial bipedality has evolved only 3 other times AFAIK – penguins, frilled lizards, and argus monitors. In the latter two, it’s a direct consequence of threat displays or territorial combat. Indeed, most monitor lizards fight in a bipedal, orthograde posture, but are unable to maintain this posture without the support of a grappling opponent. Yet some combination of selective pressures has led to a species which can and routinely does adopt this posture alone.

    The same is seen throughout the animal kingdom – a clade of numerous species with a comparatively weak form of a trait and a sub-clade within them displaying an extreme form. Rear-fanged colubrids vs “true venomous snakes”, the songs of most birds vs those of passerines, various gliding mammals vs bats, reduced-limb squamates vs snakes, etc. Or, bringing it back to anthropology, primate intelligence vs human intelligence.

    I’m not saying I agree with Carrier (I’m skeptical of the methodology too), just that “Why doesn’t *everything* with trait A evolve in the same direction?” isn’t a very good argument.

    • zinjanthropus May 23, 2011 at 8:48 pm

      Hmm… I stand by the point that using the behavior of a closely related taxon (standing upright to fight in great apes) to explain a morphological adaptation that it doesn’t have (requisite bipedalism) doesn’t make sense to me. I don’t think it’s akin to asking why everything with the trait doesn’t evolve in the same direction, though I do appreciate your point.

      As for your example of the frilled lizards and monitors, I think that brings up a pretty good point in itself: Those animals do locomote bipedally during the threat display (ie, they can facilitate bipedalism), but then return to quadrupedalism. They don’t habitually walk bipedally because their morphology requires it, as humans do. (And some dinosaurs did!)

      • zinjanthropus May 23, 2011 at 8:58 pm

        And re-reading your post I see that you mentioned that the lizards can adopt a bipedal stance as they please, but I think I am correct in saying that they don’t have any special morphology that requires that they walk bipedally?

      • Mokele May 23, 2011 at 10:03 pm

        Zinj, I see your point, but I disagree with how you’re treating obligate bipedalism as qualitatively different from facultative bipedalism, rather than simply the endpoint in a spectrum of behaviors.

        Archosaurs are probably the best examples. While originally sprawling quadrupeds, some evolved erect postures, and from there, several lineages evolved facultative bipedalism (inferred from large disparities in fore and hind limb length). Some facultative bipeds returned to quadrupedalism (often the really massive predators, but also evident in the sauropods), or even reverted to a mostly sprawling posture (modern crocodilians), while others became obligate bipeds (theropods and the bizarre Effegia). While obligate bipeds like theropods had morphological adaptations other forms lacked, since the new posture released the constraint that they must be capable of both forms of locomotion and thereby allowed such specializations, they’re still part of a continuous spectrum. IMHO, postulating that the benefit to fighting from facultative bipedalism in apes led towards eventual obligate bipedalism in humans isn’t substantially different from postulating that the speed boost from facultative bipedalism in Hesperosuchus led towards eventual obligate bipedalism in theropods.

        Plus, not all human anatomical features related to bipedalism are adaptations – I remember a fairly recent paper which pointed out that there’s a LOT of phenotypical plasticity going on, to the point where the femur of a paralyzed child was essentially identical to that of a chimp in several key aspects (valgus angle, femoral head angle, etc.)

      • Eric May 24, 2011 at 1:51 pm

        I think the question we should ask is: Are extant Apes reliable models for the morphology, the locomotive behaviour, the social structure and the cognitive abilities of the earliest hominids?

        If we just look at Ardipithecus we can see that the general morphology of the Chimpanzee/Human last common ancestor probably wasn’t chimpanzee- (or human-) like and that its locomotive behaviour was also probably very different from what we can observe in extant Apes.
        Under these circumstances, is it a reliable method to base your model solely on observations of living animals? When the last common ancestor of chimpanzees and humans didn’t looked like either a chimpanzee or a human, how can we be sure that it behaved the same way? How can we be sure that the way chimpanzees (and Gorillas) walk on two legs is any way comparable to the way our LCA walked upright?
        This is what makes evolutionary modeling so hard, you cannot simply observe present day animals and infer that past time animals behaved the same. You need some way to connect your observations to the fossil record to make them testable and give them some manner of scientific value.

  3. Danniel May 23, 2011 at 7:43 pm

    I thought that the hypothesis that our bipedalism is just an “upgrade”/promotion/fine tuning from the secondary bipedalism of arboreal apes to just primary bipedalism of no-longer-arboreal apes was already pretty almost universally accepted in such a way that I’d not expect such an alternative.

    I could also bet that if we could engineer half-way biped chimps or gorillas, the would get beaten by traditional knuckle-walking counterparts any day of the week. Even if improvised weapons were allowed. They simply have more thrust. The reason why they “get” bipedal when fighting is mostly because they both fail to take down the opponent immediately, and the “draw” results in both being somewhat upright.

    I think the result of such bizarre fights would be even more drastic if we had an arboreal ape as the starting point, making something like an orangutan closer to a chimp or a gorilla, than making them fight each other. The original orangutan would be totally beaten so bad by the orangutan with a more chimp-like body conformation. The biomechanics of the punches of a “quadruped” ape has to be much superior to the punch of an arboreal, brachiator ape. One has to propel it’s own body forward with his arms, the other needs more to just hang there, swing back and forth and then jump somewhere else, which requires much less strength. Also the way that the pectoralis attaches to the sternum seems to be much more efficient in terms of punch or grappling power on “quadrupedal” apes.

    Actually, perhaps this hypothesis is better the other way around. Gorillas and chimps evolved independently their knuckle walking not only for locomotive reasons, but because it made them better fighters.

    • zinjanthropus May 23, 2011 at 8:55 pm

      …was already pretty almost universally accepted in such a way that I’d not expect such an alternative

      Ha! The thought of paleoanthropologists universally accepting something is funny! But I’m actually not quite sure what you mean by secondary bipedalism- do you mean grabbing branches above their heads as they walk on the branches below bipedally? Or do you mean the bent-knee/bent-hip gait that chimps and gorillas display when walking terrestrially? Both ideas have major flaws, and I am in the camp that human bipedalism evolved from a pronograde, Proconsul-like arboreal quadrupedalism.

      • Eric May 24, 2011 at 1:57 pm

        Any Idea how much the heaviest Pronograd climbing monkey weights? I’m just asking, because one of my professors said that Ardipithecus probably was to big and heavy to be an effective pronograd climber. On the other hand, he is in the arboreal biped group (at least when it comes to Ardi) so he might be a little bit biased.

      • Danniel May 24, 2011 at 9:59 pm

        I can never really catch all the terminology, but I was thinking of an hypothesis I think was described on Pilbeam’s “the ascent of man”, where orangutans and gibbons, and “their” bipedalism, secondary or whatever it’s called, was supposed to be the best approximate ancestral condition present on the common ancestor of humans, chimps and gorillas, rather than knuckle-walking or chimp’s and gorillas sporadic bipedalism.

        I’m not so sure it’s really an accurate description or even if it was really being defended as the best explanation then, but recently this idea or very similar ideas were being again presented as top contenders at least. I remember from the somewhat hypey framing of “an human ancestor for the apes” on anthropology.net and some other blogs like pharyngula.

        Additionally, I remember having read some stuff in the sense that australopithecines might be better seen as more closely related to gorillas than to humans, which combined with the recent news about Ardi, seemed to me somewhat favorable to the whole “human” ancestor for the apes scenario; Lucy ceases to be a “necessary” link between humans “and” apes evolved from a more gorilla or chimp-like posture, and is “demoted” as just an ancestor of gorillas, that still retains a more upright posture though.

        … and from these snippets of information I just assumed that it was already the new mainstream explanation, rather than something more like that classic illustration of the “march of progress”, or something similar at the very beginning, but where the upright posture comes first and chimps and gorillas split and progressively evolve in the “backward” direction of the illustration, while man keeps a more ancestral condition.

  4. Danniel May 23, 2011 at 7:50 pm

    I wonder if bonobos, who are less aggressive, are also somewhat less knuckle walkers, with more anatomical remnants of an ancestral bipedalism.

    • zinjanthropus May 23, 2011 at 9:07 pm

      “ancestral bipedalism”?

      This book chapter says that bonobos are more suspensory, while chimps are more terrestrial, but that when walking quadrupedally, chimps and bonobos both knuckle-walk equally.

      • Danniel May 24, 2011 at 10:02 pm

        Now that you put that into quotes I just felt a creepy cold feeling in my stomach. I’m not talking about *that* ancestral bipedalism, but rather that humans, chimps and gorillas descend from some sort of ape that was pretty much an upright biped, but chimps and gorillas evolved their condition independently, instead of humans having evolved uprightness from a more chimp or gorilla-like posture.

  5. Danniel May 24, 2011 at 10:38 pm

    And thanks for the article. I just found another, this one states that although neither of them walk bipedally significantly more than the other, they tend to use bipedalism for different reasons; chimpanzees for display and bonobos for carrying and vigilance.

    http://www.ncbi.nlm.nih.gov/pubmed/11468753

  6. Claudius Denk August 7, 2011 at 9:37 pm

    Bipedalism arose due to the need to defend territorial food resources (using rocks and sticks) to survive the dry season as a communal group.

    Search the phrase Ecological Gatekeeper Hypothesis in the newsgroup: sci.anthropology.paleo

  7. Daud Deden October 8, 2011 at 7:25 pm

    Morotopithecus vertebra shape indicate an upright stance (but not necessarily habitual upright bipedalism), advantageous for plucking hanging fruit from below very narrow branches, this provided an advantage for prolonged upright posture and disadvantage for quadrupedal pronograde above-branch walking. Great apes have since adapted the slow bipedal walk and faster quadrupedal knucklewalking gait, while humans running but not knucklewalking because their food was largely not in the rainforest canopy, but in the small forest openings and edges, especially at waterside.

Follow

Get every new post delivered to your Inbox.

Join 29 other followers

%d bloggers like this: