November 18, 2004

Distance running shaped human evolution. "Our African ancestors may have been talented endurance athletes." But now that we have MonkeyFilter, we can spend the day sitting.
posted by homunculus 19 years ago
  • Oh, man, I can barely raise the effort to get up and go to the corner shop. *sigh*
  • ...in competition with hyenas... Explains a lot.
  • Right. I'm back. I needed to go and buy sugar. I've got it now, and will shortly go and make some coffee. This seems a nice little piece of work, although I'm not sure how original it is - the concept that endurance running across the savannah is key to elements of human posture has certainly been around for a while. But this adds detail, which is always welcome, so long as they don't try to oversell it. It also ties in nicely with the radiator theory for human upright posture - that on the savannah, in the heat of the sun, walking/running upright provided the smallest surface area for direct sunlight, hence preventing overheating. And, of course, the meerkat "if you stand up you can see predators from a long way away" theory. That's always good. The trouble with all these theories, however, is that they don't seem to provide the initial impetus for bipedal locomotion. They explain well how bipedalism would have been beneficial once it developed, how it would have enabled our ancestors to colonise a new niche (the savannah), and certain details of how our specific bipedal traits emerged. But they seem unlikely to have been sufficient to drive the change in itself... which is where I shut up, before I start wittering about aquatic apes, and get lynched by a troupe of enraged paleoanthropologists.
  • As someone who's training lies in Anthropology (though sadly not my work), I absolutely love running across articles like this. This actually ties in neatly with the theory that our ability to have sex at will (rather rare in animals) may be due in large part to walking upright. Being bipedal requires a much higher base metabolic rate than choosing to stick to four leg locomotion. And a high sex drive may have just been a sort of evolutionary freebie—choose a higher metabolism, get to have sex whenever you want. Sort of a two-for-one sale at the evolutionary store. It's always interested me how interconnected a single evolutionary change can be with subsequent ones. Mutate one thing, and a whole host of other possibilities open up--or are closed off, as the case may be. If this is something that holds up to scrutiny, I can't help but wonder if it isn't another clue as to why our bodies respond so poorly to inactivity--re: our current obesity "epidemic." Sorry for the lecture. This is a pet subject.
  • I absolutely love running Exactly.
  • ...our ability to have sex at will... We have an ability to- Oh. Um. Yes. Ahem. That ability, of course, yes, absolutely. Seriously, though, douggles, that's a fascinating thought. What interests me about the change from sex only during oestrus (or at the full moon, or once every seventeen years, or whenever) to sex 24/7 is how it ties in with altered social patterns and increasing social complexity. Such behaviour takes such routine behaviours as male competition, female mate choice, and conditional care of infants, out of the realm of simple instinctive responses within a set structure, and into that tricky sphere of interconnectivity that we're still writing sitcoms about 5 million years later. One only needs to look at how constant non-reproductive sexual activity affects Bonobo communities to wonder which came first - the complex social behaviour, or the lots of fucking? On another note, I'd forgotten about the higher metabolic rate required for bipedalism. It's another puzzle - even if there were great benefits further down the line, what triggered the change to a more inefficient and more dangerous mode of locomotion? Did we have to change because we were forced out onto the savannah, or did we change elsewhere and then discover that we could colonise the savannah really well with our new special walky legs?
  • wow, homunc, thanks for that post on the monks. I have never heard of them before. fascinating. CRAZY! but fascinating and sort of beautiful. thankyou.
  • The last major theory I ran across in school concerned climatic change as a driving force for the switch to two legs. As the theory goes, our habitat began drying out, causing the forests to recede and forced our move into the savannah, where two legs gave an important height advantage for spotting possible predators. I always thought that was a bit too simplistic though. It wasn't like we as a species woke up one morning and said, "Damn, where'd the forest go? I know I left it around here somewhere." An influence, surely, but the cause? I can't quite buy that. If savannah living were the driving impetus behind our bipedal locomotion, I can only surmise that the reason for us choosing it has to have been more complicated than merely less rain. Having said that though, once we were living on the savannah, two legs would sure help to spot the occasional not-so friendly sabre-tooth tiger. And yes, flashboy, I've got to agree. Sex has had an astoundingly deep influence on our species' social structure. 'Course, you can argue that's the case with most species, I suppose. Love is supposed to make the world go 'round, and Earth spins a hell of a lot faster than most planets.
  • This is really interesting. But I'll stick my head out and ask (esp of any paleoanthropologists around): What is the current thinking on the aquatic theory? what are the arguments and evidence against it? Is there a currently accepted model about the origins of bipedalism, etc., or is everyone just in total debate?
  • Wow, now I wish I didn't bail on running last night.
  • On NPR yesterday afternoon, this story was followed by a few seconds of "Born to Run".
  • "This actually ties in neatly with the theory that our ability to have sex at will (rather rare in animals) may be due in large part to walking upright." But how does this explain bonobos? They're even more into the free-love thing than we are, and they aren't bipedal.
  • I think the point about bonobos is that, while they engage in sexual activities at all times, actual reproductive mating is still linked to an oestrus cycle - which is not the case in humans. Much bonobo sexual activity is mutual masturbation (often linked to socially bonding activities such as foraging), as opposed to reproductive intercourse. Don't know if that's a sufficient answer to the question, though.
    Sex: Bonobos live a relatively peaceful life compared to chimpanzees. This is due largely to the fact that female bonobos are eight times more available to males for mating and there are equal numbers of females to mature males so there is less fighting for mating rights. Sex is an important way to ensure group stability and ease tensions. Bonobos substitute sex for aggression, and sexual interactions occur more often among bonobos than among other primates. Reduced male aggression, strong bonds between males and females, and frequent sex (including male-to-male and female-to-female) characterize bonobo society. However, the rate of reproduction in the wild is about the same as that of chimpanzees (a single infant is born every five to six years) beginning at age 12. Frequently asked questions about bonobos: What is that big thing on the bottom? The female genitalia is on the outside. During her monthly cycle (estrus), the bonobo genitalia will swell. What are they doing? Bonobos engage in sexual activities of all sorts— frequently for purposes other than breeding. They use heterosexual and homosexual activities to release excitement and tension. Any erotic behavior employed by man is also used by bonobos.
    I can't help but imagine that second Frequently Asked Question being frequently asked in the tones of a shocked schoolmistress...
  • What is the current thinking on the aquatic theory? what are the arguments and evidence against it? Is there a currently accepted model about the origins of bipedalism, etc., or is everyone just in total debate? Right. I'll do my best, although it's several years since I was a biological anthropologist, and I may not have been paying quite as much attention as I should. The Aquatic Ape Hypothesis is treated primarily with scorn and derision amongst paleoanthropologists. It is dismissed; I never got to have a full conversation about its merits with my lecturers or supervisors. The major reason for it being dismissed is lack of evidence (although there may be, as many of its proponents claim, a reaction against the fact that many of its supporters are not academically qualified). Most of the evidence for AAH could be described as 'circumstantial' - pointing to a large number of human traits that are (claimed to be) unique within the apes, and which are (claimed to be) indicative of, or only found in, mammals which are either aquatic, semi-aquatic, or which regularly seek out water. Many of these could have other potential causes - it is the accumulation of suggestive traits which, proponents claim, points towards AAH being valid. There is also, I believe, some geological evidence for a major inundation in the region of Africa where many hominid fossils have been found, during the period of 6-7 million years ago where the "missing link" should be found. But I'm not qualified to judge these claims. It should be pointed out that AAH itself has variations within it (it's too small a field for there to be one canonic version), mostly relating to just how "semi" the semi-aquatic nature of our ancestors was. The most plausible version (for me) holds that they were near-permanent waders, not swimmers, living in coastal conditions that would most closely resemble the mangrove swamp environment of today. It should be noted that several primates in similar conditions today (including, allegedly, some bonobos) have adopted bipedal locomotion through water, and there are reports that some monkey populations have begun maintain the same stance on land as well. Continued...
  • ...welcome back The Wikipedia article for it is quite comprehensive, although perhaps doesn't give enough weight to the counterarguments. This list proposes counterarguments to the major circumstantial evidences for AAH, although I have no reason to trust its authority. My perspective on AAH is that the circumstantial evidence relating to many of the traits (body fat, sweat, copulation, tears) is essentially worthless, and often unfounded. However, it is persuasive enough as an facilitator for the development of bipedalism alone that I think it deserves examination. There is currently no fully persuasive, widely held model for the development of bipedalism. As douggles says, most models posit environmental changes forcing our ancestors from the jungle out onto the savannah (which would probably rule out AAH). Also, as noted above, there are many sound theories as to why it may have been beneficial once it developed - but very few which would seem to be a sufficient driving force in and of themselves. Evolution is not predictive - it cannot look forward to see that the end product of an evolutionary path will be beneficial. It could well be that a combination of factors (greater long-distance ability, sentry behaviour, heat regulation) were sufficient to drive the change, once savannah living was necessary, but to my mind that seems both slightly fortuitous, unduly contingent and with more than a hint of 'hopeful monsterism'. It may be that new fossil finds will clarify the issue - current hominid intermediates don't present an entirely coherent picture. This article is quite old (1995) but is nonetheless a very nice run-through of the major issues and theories. Anybody else wants to jump in this, feel free... :-)
  • Any time, people. Just speak up, don't be shy. Guys? Guys? Paleoanthropologists?
  • Anybody else wants to jump in How's the water?
  • What's a 'hopeful monster'?
  • "Hopeful Monsters" refers to, essentially, macroevolution; evolution progressing not by small, gradually accumulated change, but by sudden, large alterations to the phenotype (and possibly genotype). It's an unloved concept in evolutionary theory: either because it is seen as relying far to much upon outrageous chance to produce viable organisms; or because the attempts to describe a constraining or guiding process (by which the mutations are channelled in useful directions) were not terribly successful; or because (especially in the form revived by Stephen Jay Gould) it gave undue retrospective weight to speciation events that are as much artefacts of our classifcation system as they are accurate representations of sudden and dramatic change. In more informal terms, it's the "and with one bound they were free!" of evolutionary theory. Here's some stuff on Goldschmidt, including links to one of Gould's essays and some more critical discussion of his ideas.
  • You were doing so well we thought we'd let you mull over it for a few hours. Plus, there's MeFi registration so other threads are kinda like a high school basketball during the Super Bowl. That said, the Aquatic Ape theory is bunkus. AA theorists have a tendency to cobble together traits about humans that could be useful in the water if they were greatly magnified and then link those traits to a select few aquatic animals (mammalian, reptile, avian, or crustacean, it don't matter to me!) while ignoring or brushing off evidence of those same traits in other non-aquatic animals. AAT research is not only often riddled with flaws and assumptions, but grounds itself in a complete denial of the existing fossil record of homonids.
  • Some AAT bull: -Bipedalism AATers like to cite the relative lack of bipedalism among other primates while pointing at the proboscis monkey, which lives in mangrove swamps and which swims fairly well and wades bipedally, as evidence. This ignores that proboscis monkeys DO walk (when not waist deep in water) just like other primates, that is, quadrapedally. This claim also ignores that other apes (like chimps, bonobos, gorillas, etc) are "knuckle-walkers," which is a far cry from the quadrapedalism of say, a giraffe. Apes knuckle-walking is tied to their pelvic and spinal structure as well as their arm structure all of which are adapted to their enviroments, which are uniformly heavily forested. Furthermore, there is evidence of knuckle-walking in early homonid fossils. Of course AATers are adept in ignoring the fossil record, except when it suits them, which brings me to another point.
  • -Aquatic Fossils Often cited is(such as in this article by Elaine Morgan, the lead AATologist) that the bones of the superstar of early homonids, Lucy (the same Lucy whose forearms show evidence of knuckle-walking), was found in an area which was flooded 7 million years ago. Of course Lucy's bones have been dated to around 3 million years ago at which point the transgression of the Red Sea woud have receeded. AATers often go on to cite the abundance of early homonid fossils, which are clearly maladapted for aquatic dwelling, found around areas which would have been lakes or rivers at the time.
  • This of course proves nothing except that hominids, like modern humans, prefered living near a lake, where food and water is abundant, as opposed to the middle of a desert, where sand and rocks are abundant. Also, there's little to no evidence that these early homonids relied on aquatic sources of food, as would be expected if they had just recently evolved from an aquatic species. Not until anatomically modern humans developed has there been evidence of major use of aquatic food sources. Note as well that these homonids would have lived by fresh, not salt, water. Odd then that AAters would mention it since the parts of the AAT revolve around our supposed miraculous adaptions to deal with excess salt. Truth is that tigers in the Sundarbans are better at processing salt water, and are better swimmers to boot.
  • Those examples are just the tip of the AAT iceberg of bullshit. The entire field of AAT research is a small number of people stringing facts together, and ignoring others, to get the conclusion they want. I don't know how anyone can take seriously a theory that cites the oddity of our larynx structure while ignoring the immense changes our throat and mouth underwent in the development of speech, or cites our singular ability to cry "tears of emotion" as evidence of aquatic origin while ignoring the incredible developments of the frontal lobe of the cerebrum that make those emotions possible while also ignoring that numerous other animals shed tears of a phyiscal nature.
  • Thanks flashboy and Spooky. The annotated flyer is especially clear. I can see now where the argument falls apart, though like fb I am still sympathetic to staying open to ideas (as the savannah theory has always seemed weak as well).
  • Thanks, flash.
  • Oooh. Great posts, Spooky. Nice work. To clarify what I said upthread - I agree with you that the vast majority of AAH is, as you say, an iceberg of bullshit. And its proponents are often cranks, and almost always unqualified. That aside, the fact that certain gits propose extreme versions of a hypothesis should not rule out any element of truth in it. I still think that a wading ape hypothesis is worthy of consideration in looking at bipedlism alone. Not as a driving force, necessarily, but as a possible "scaffold" for change. As your link shows, the Australopithecines were not themselves habitual knuckle-walkers, but shared a common knuckle-walking ancestor with gorillas and chimps and retained certain of the features. But they were also by this time functionally bipedal (to some extent). So the change was kicked off at some point between 7 million years ago (last common ancestor with chimps, by genetic dating) and 4 mya (Australopithecines). Knuckle-walking, as you say, is a very specialised form of locomotion, and in many ways is less suitable for making the transition to bipedalism. How that transition occurred could be due to environmental pressure (which would tie into savannah theory), but it could also be due to an environmental factor that aided the transition (of which water could be one). Oh, and as I mentioned above, there is some anecdotal evidence for proboscis monkeys maintaining bipedal locomotion when not wading. Which I wish I could find some reference for... But anyhow. I'm not arguing for AAH, but I do think the possibility that intermediate hominid forms of 7 - 4 mya were full or part-time waders can't be fully discounted, and it could have some explanatory value. Maybe. Perhaps. Hmmm.
  • flashboy and Spooky : more than just pretty faces.
  • Monkeyfilter: Not too bad from behind, either.
  • Sure, it's possible that our ancestors from 7-4 mya were spent a great deal of time wading, but it seems to me that a wading scenario would not have necessarily contibuted to bipedalism and might have even stunted some of the adapations that contibute to it. I'll start by assuming that the homonids in question spent large parts of their day waist deep in the water, as any deeper would probably require fulltime swimming to be efficient. This would explain the the thickness and curvature of the lumbar vertebrae since weight would be concentrated on that area as the rest of the lower body would be suppoted by water. But that fails to explain bipedal adaptations like the thickness and strength of homonid femura, which would not have been necessary if it were constatly bouyed by water, or the plantar arch of the foot, which acts as a shock absorber, also would not have been necessary in an immersed enviroment.
  • Then, if those adaptations are useless in a wading enviroment (and this is really all just conjecture on my part), the question of what would be beneficial in a semi-aquatic enviroment arises. It seems to me that homonids standing half in the water would be incredibly vulnerable to any fully aquatic creature (crocodiles, freshwater sharks, homocidal mermen etc etc) that came along. A homonid in the savannah has the advantage of spotting the lion when it's still far off, a homonid in the water wouldn't spot the alligator until its too late. Off the top of my head I can't think of any animal that spends most of its time half out of the water (well maybe some birds). Even the hippo tends to spend time fully immersed and it shows all sorts of adaptions in its eyes, ears, and body to that enviroment.
  • The aforemention proboscis monkeys in the mangroves have evolved webbed feet to help propel them more swiftly through the water. Of course, webbed feet wouldn't show up in the fossil record, and that's the whole problem with the AAT. Every AAT article I read and discussion I have always seems to end with some variation of "well there's no evidence to contradict these claims." While that's (mostly) true it does not follow that AAT is correct. With the gap in the fossil record and our inability to go back in time and actually observe early homonids I could argue for AAT just as easily as I could argue for intervention by extraterrestrial geneticists being responsible for our evolution.
  • Fixed FPP link. I was reminded of this story by this post on MeFi.
  • We hve a Buddhist monastery in town, a couple of doors down from my doctor's office. They wear gorgeous orange-and-maroon robes. I sometimes linger on my way out of the office, just to watch them come and go.