Why do we walk upright?

Discussion in 'Biology & Genetics' started by Oniw17, Feb 21, 2007.

  1. Grim_Reaper I Am Death Destroyer of Worlds Registered Senior Member

    Well I would say So that we can Carry tools and more objects. As well as defend ourselves from attack better. All so it was more likly do to moving fron the trees to the Grass lands hunched over you cannot se much so the need to walk upright was evolved so we could see where we were going.
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  3. Fraggle Rocker Staff Member

    Please review my posts about Ardipithecus, and watch the Discovery Channel program or at least read a little more about her than you'll get from my few bits.

    Our ancestors did NOT "move from the trees to the grasslands." Ardi, the oldest ancestor we have ever found in our own genetic line, was fully bipedal and lived in the forest. This obviates the old hypothesis that bipedal walking evolved so hominids could see over the top of a field of grasses.

    Bipedal walking allowed them to travel large distances comfortably and carry back a large quantity of food in their hands.
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  5. iceaura Valued Senior Member

    The advantages of bipedal walking after it has become efficient do not explain the transition.

    Whatever stood humans up on their hind hands, it wasn't the advantages of efficient bipedal locomotion. In the early stages, hominids were not bipedal - they were quadrupeds being forced or led to walk on their hind legs.
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  7. Search & Destroy Take one bite at a time Moderator

    I tend to agree. Seeing baboons wading through water during the rainy season (ah*em planet earth) it seems most likely this forced us on our feet first.

    From my memory, these are other reasons to stand up found in the animal kingdom:

    To look intimidating and appear big (maybe)
    To see further (maybe)
    Courting ritual (unlikely, doggystyle?)
    To reach high-up food (no way)
    To wade through water (observable)
    Last edited: Nov 13, 2009
  8. Hercules Rockefeller Beatings will continue until morale improves. Moderator

    The advantages of bipedal walking were not reaped solely after it had become efficient. That’s a creationist-style argument that tries to suggest that there are no advantages to transitional states. Like all other traits that evolve transitionally, the advantages of bipedal walking would have increased as the efficiency increased.

    From my scanning of academic sources on the topic, the majority of anthropologists disagree.

    From my scanning of academic sources on the topic, there were early hominids that had evolved efficient bipedal walking and were not considered quadrupeds.

    It seems this way to you, maybe. To me it’s not the “most likely” impetus at all.

    I regard a certain ‘water-based hypothesis’ of hominid evolution to be pseudoscience. If this thread steers down that track then it’s likely to end up in the Pseudoscience subforum.
  9. Search & Destroy Take one bite at a time Moderator

    We have different opinions there is nothing wrong with that.

    I don't like the water-based hypothesis either. Just hearing those words and the sirens go off in my head too.

    I'm talking about wading through African plains during the rainy season. What's your opinion on this?
  10. Fraggle Rocker Staff Member

    Face-to-face copulation is extremely rare. I can't think of any other mammal that can do it. (Although I don't know anything about the fully or nearly aquatic mammals like dolphins and sea lions.) Humans have the capability because of two unique anatomical distinctions:
    • Our wide pelvis. It allows all the legs and other body parts to fit comfortably into the crowded space. This evolved as our brains enlarged, to fit the baby's cranium through the birth canal. As it is, our babies are born at a much lower level of brain development than other mammals, they are more helpless for a longer period of time, and their heads continue growing longer after birth. Ardipithecus, with a brain less than half the size of ours, did not have such a wide pelvis.
    • And of course the bipedal stance. A couple of key muscles have been rerouted to make it easy to lock our knees, most famously the gluteus maximus which gives our butt its characteristic dual-hemisphere shape. This also makes it possible to lie down with our legs fully horizontal and fully straightened, without which face-to-face copulation would be awkward and uncomfortable.
    The Discovery Channel is kid-friendly and completely avoided the subject of mating, so I don't know whether Ardipithecus was far enough along in these transitions to facilitate the "missionary position."
    Presumably scholars are working overtime to overhaul those written records, now that Ardipithecus has given us an almost entirely new look at the early history of hominids. Such as pushing our branching off from the other Great Apes back two million years and tossing the Savannah Hypothesis into the dustbin.

    The fossil was first discovered in the 1990s but it took more than a decade--and lots of computing power--to assemble and correlate it. But that computing power also gives us a better reconstruction of her musculature, from the geometry of the ligament attachment points on the bones, and from real-time 3-D simulations of the inertial shifts generated by walking and other movements.

    The two-hour TV special was certainly spellbinding. Paleontologists, primatologists, physicists, those folks who figure out with amazing accuracy what your missing eight-year-old looks like at sixteen, and a guy whose profession is the reconstruction of hominids and other animals from all of this information, gave us a one-minute animation of Ardipithecus walking through the forest, showing the movements of the muscles, the balancing, and the way the upper body moved in response to all of this.
    It does seem that way now that we have incontrovertible evidence of a transitional species (the "Missing Link") that was an erect-walking forest-dweller but retained the ability to climb trees almost as well as a chimpanzee in an emergency.

    But I wouldn't have been so quick to discard the Aquatic Ape Hypothesis last year. I'm still waiting for answers to two questions:
    • Why are we the only apes with these (seemingly) vestigial little webs between our fingers?
    • Why are we the only apes buoyant enough to permit the integration of long periods of swimming into our normal daily routine?
  11. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    I wonder if this is true, when eating your caloric requirements every day was uncommon? I tend to think it true of modern society people, but what about those who lived on the edge of starvation, with occasional great feasts? How well nourished were these "swim capable" ancestors? Are lean and trim athletes who run 5 miles several times each week more "swim capable" than a great ape?

    I.e. what fraction of their body mass was fat, which floats, and what fraction was bone and muscle, which sinks? Are you sure that modern low-exercise "couch potatoes" are not warping your perspective?
  12. Grim_Reaper I Am Death Destroyer of Worlds Registered Senior Member

    I stand corrected on the grasslands issue thank you.
  13. iceaura Valued Senior Member

    The advantages that depend on its being efficient are reaped solely after it becomes efficient.

    Some other advantages did not, but what were they? That's the question.
    You still have to get past the transition - there has to be a payoff for the initial handstand, one that maintains it in the face of its obvious penalties in efficiency, speed, visibility, endurance, agility, and so forth. There has to be an initial advantage - the ones that accrue to increasing efficiency are far in the future.
    What the "majority of anthropologists" have apparently accepted as credible accounts of the initial evolution of bipedal locomotion in hominids is an embarrassment to the field. "To see over tall grass?" "To free their hands for carrying tools and food across the savannah?"
    Uh, yes, we are talking about that.
    A human female whose body fat "swim capability" drops to great ape levels will often quit menstruating, become incapable of reproduction, and suffer bone loss and other side effects.
    I have no idea why you think this forest ape in any way contradicts a Wading Ape hypothesis - it is exactly what one would expect, from a tree - wade transition.
    Last edited: Nov 13, 2009
  14. Fraggle Rocker Staff Member

    Well I'm no anthropologist so I'll be happy to wait and see if the Aquatic Ape hypothesis is resurrected by subsequent fossil discoveries.

    But I was under the impression that it postulates migration from the trees directly to the water. This would explain several issues:
    • There are few large predators in lakes, a safer environment than the savannah with its enormous, fast-running cats, including lions who hunt in packs.
    • Warm-blooded air-breathers with our greater energy supply are the apex predators in the water, making it easier to catch food and fight off the few predators we find. (Cf. orcas, sea lions and penguins.)
    • This predatory life made it possible to adapt to a high-protein carnivorous diet.
    • Our unique gigantic brain could not have evolved without this protein source. (The dog has a smaller brain than the wolf because as our companion he has become more scavenger than hunter.)
    • The articulation and musculature in our front legs and feet were modified for more efficient swimming, making knuckle-walking inefficient on land.
    • This was an impetus for the final adaptation to bipedalism, as well as creating hands to become supremely efficient food gatherers rather than mere grazers like the other apes.
    • When we tried migrating back to the land, these modifications made us more competitive on the savannah.
    If these adaptations evolved in the forest before we ever tried our luck in the savannah, it leaves the Aquatic Ape hypothesis dangling without an evolutionary impetus.
  15. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    To fraggle rocker: you attribute to me in Post 111 a statement about tree to water transition. I am nearly 100% sure I never said anything like your statement.
    I have searched back a few pages and do not find any such statement. Please correct (or tell post where I said that).

    In post 108, I did ask you to support another statement that I have doubts about.
    Last edited by a moderator: Nov 14, 2009
  16. Idle Mind What the hell, man? Valued Senior Member

    Fraggle's quote was taken from the last line of iceaura's post #110.
  17. iceaura Valued Senior Member

    That was an odd and incomplete list of the various advantages accruing to a wading ape.

    The main one is the ability to wade and forage in shallows and along shorelines, not swim per se - none of this "apex predator in the water" business is involved (they never got to that stage) nor are the arms necessarily so radically adapted for swimming. The ape is still imagined to be climbing trees, probably, or rocks, for refuge and the kind of sporadic fruit/egg bonanzas that reward the big primate brain elsewhere. Amphibious, not aquatic.
    Our gigantic brain would have been yet far in the future, entire species down the line.

    The dietary advantage would be in shellfish and such, raccoon/otter food writ large and oceanic, not the predation or carcass scavenging that came later and drove or allowed the brain inflation. That is a rich source of food not available to other primates - a unique niche.

    One explanatory advantage of wading is that it gets the monkey up on its hind legs, supported by the water and with a reason for carrying stuff fair distances, when it can't walk very well - AFAIK so far, the only explanation that does that.

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