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Author | Topic: Evolutionary History of Apes | |||||||||||||||||||||||||||||||||||||||||||
pandion Member (Idle past 3001 days) Posts: 166 From: Houston Joined: |
It is doubtful that the derived character of knuckle walking in chimps (both species) evolved after the separation of chimps and humans. You see, gorillas are also knuckle walkers. Thus, such a proposal suggests that this unique method of walking evolved in two separate species. Humans and chimps probably separated some 6 or 7 million years ago. They separated from the gorillas around 10 million years ago. It's not likely that both gorillas and chimps developed identical methods of locomotion, including the structure of the wrist that locks when these knuckle walkers put their knuckles on the ground, after being separate species for 5 million years or so.
Let me explain what I'm talking about. Lean down and put your knuckles on the ground similar to what a football player does in a down stance. Keep your thumb along the side of your hand. Now lower the heel of your hand to the ground. Easy, right? Neither a chimp nor a gorilla can do that. There is a knob-like protrusion on the distal end of the radius of all three of these species that prevents the hyper-extension of the wrist. We humans lack this protrusion and can thus flex our wrists forwards and backwards. Several years ago an anatomist who was familiar with both human and chimp anatomy had an opportunity to examine "Lucy" (AL 288-1), whether the actual fossil or a cast I do not know, and observed a protrusion on the end of the radius similar to that of chimps and gorillas. At the time, I was in communication with two graduate paleoanthropologists who were as surprised as everyone else by the paper. Both of them confirmed that it was true. It had never been noticed before. More recently, when "Lucy" began her tour of the US at the Houston Museum of Natural Science, I had an opportunity to observe the actual fossil from mere inches away. On my second visit I went armed with life-sized pictures of human wrists. I can confirm that "Lucy" did have this wrist locking extension on the end of the radius. I can only conclude that knuckle walking is a derived trait that has been lost in humans and retained in related species. Otherwise we are postulating that gorillas first separated, then chimpanzees (and then chimpanzees separated into two species) from the lineage that lead to mankind. Additionally we are postulating that after all of these separations, all of them developed identical structures that lock the wrist. After that, the lineage that led to humans lost this mechanism. We know that "Lucy" was a biped. Why on earth would that species have developed this wrist walking mechanism along with the three other species, only to lose it again. Is it not more logical to understand that the wrist-locking mechanism was vestigial in "Lucy"? So, is this mechanism missing in "Ardi"? Then "Ardi" cannot be ancestral to "Lucy". Both can be, and obviously are, transitional between our common ancestor with apes and us. But we can't state to a logical certainty that either is our ancestor. That's how I understand it. If I am wrong, then I would appreciate knowledgeable correction. Edited by pandion, : No reason given.
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Huntard Member (Idle past 2296 days) Posts: 2870 From: Limburg, The Netherlands Joined: |
If anyone is interested in the show, it'll be aired again on october 16th.
Also, here's a link you can get it from (torrent, if this is not ok, remove it , admins).
Here Download links are at top left. Edited by Huntard, : Typo I hunt for the truth I am the one Orgasmatron, the outstretched grasping handMy image is of agony, my servants rape the land Obsequious and arrogant, clandestine and vain Two thousand years of misery, of torture in my name Hypocrisy made paramount, paranoia the law My name is called religion, sadistic, sacred whore. -Lyrics by Lemmy Kilmister of Motorhead |
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RAZD Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: |
To bring this back to Ardi, I'm posting this from Message 86 on the why is the lack of "fur" positive Progression for humans? thread and then respond to a new post from herebedragons on another thread:
quote: Now, from herebedragons Message 171 on Windsor castle The example I am thinking of is bipedalism in humans. While we now consider bipdalism to be a significant advantage, I doubt our ancestors would have. Monkeys can climb trees, run and move faster, jump from branch to branch, and so on ... While walking on two legs would be a major hinderance. Especially to the first creatures to do so. Curiously, some modern thinking is that bipedalism evolved by walking and running along branches, a behavior that is observed, and that this led to walking between trees as a preadaptive behavior to the open woodland ecology cited above. Certainly all early bipeds are also adept at climbing, even up to lucy we have evidence of an opposing toe ability.
Could it have been as we developed tools we needed to be more upright? Doubful. Bipedalism is at least 4.4 million years old, and the earliest identifiable tools are much much later. Wood sticks with sharp points maybe (chimps have been observed making and using such tools), but not anything kept like the stone tools at Olduvai.
I don't really think that our ancestors stood up more and more (as I have read in some texts) and this drove the evolutionary change. NS says that the change is there in the population and is just selected on based on fitness for survival. So if they became more upright there was a distinct advantage to that change, based on survivability. Correct, and being pre-adapted to walking from an arboreal mode would make such locomotion possible in an open woodland ecology where there are larger spaces between trees. This would allow an occasional biped to move into such a new territory and take advantage of a new opportunity. Bonobos (pigmy chimps) are about the same size as Ardi, apparently, and are occasional bipeds - more than the other chimps. Enjoy. we are limited in our ability to understand
by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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herebedragons Member (Idle past 858 days) Posts: 1517 From: Michigan Joined: |
Again, thanks for the response. I will reply as soon as I can.
Replying to this post was the only way I could figure out to bookmark this thread. Is there a better way?
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caffeine Member (Idle past 1025 days) Posts: 1800 From: Prague, Czech Republic Joined:
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I can only conclude that knuckle walking is a derived trait that has been lost in humans and retained in related species. Otherwise we are postulating that gorillas first separated, then chimpanzees (and then chimpanzees separated into two species) from the lineage that lead to mankind. Additionally we are postulating that after all of these separations, all of them developed identical structures that lock the wrist. After that, the lineage that led to humans lost this mechanism. We know that "Lucy" was a biped. Why on earth would that species have developed this wrist walking mechanism along with the three other species, only to lose it again. Is it not more logical to understand that the wrist-locking mechanism was vestigial in "Lucy"? There are less complicated and tortorous routes which would acheive the same thing. The common ancestor of humans, chimps and gorillas would have been a knuckle walker. Whilst the ancestors of gorillas retained this feature, the ancestors of chimps and humans began to develop bipedality. Some of these bipeds, however, which would include the ancestors of chimps, began to get back down on all fours as their ecology demanded, and whilst they still retained enough of a knuckle-walker's anatomy to not make this prohibitvely unlikely. They'd still have the protusion on the radius, as demonstrated by the fact that it's retained in bipedal Lucy, so there's no need for this to be evolved again. I don't know how realistic this scenario would be based around the anatomy of the fossils we know, but I don't think humans and chimps sharing a bipedal ancestor requires the wrist-locking mechanism to evolve three times independently - it still only needs to arise once. Knuckle-walking as a whole could have evolved once, been lost once, then been subsequently regained once, by an ape still in possession of some of the features that made their ancestors successful knuckle-walkers.
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Briterican Member (Idle past 3949 days) Posts: 340 Joined: |
herebedragons writes: Replying to this post was the only way I could figure out to bookmark this thread. Is there a better way? I tend to bookmark particular threads in my browser (ctrl-D on most browsers).
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RAZD Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hi Briterican,
I tend to bookmark particular threads in my browser (ctrl-D on most browsers). Then the problem becomes sorting through all those bookmarks ... (if you're like me, you will have a LOT relating just to evolution) Another way is to reply to a thread, and then you can check your personal posting list BritericanEvC Forum: Briterican Topic Index herebedragonsEvC Forum: herebedragons Topic Index and this will even tell you if you have replies. Using these lists also helps understand another posters predilections if you look them up and see what their primary interests seem to be from their activity. EvC Forum: RAZD Topic Index
Fav Forums (% of member's total of 11155) You can also see their recent threads. /offtopic/ Enjoy.
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RAZD Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Excellent point, caffeine.
There are less complicated and tortorous routes which would acheive the same thing. The common ancestor of humans, chimps and gorillas would have been a knuckle walker. Whilst the ancestors of gorillas retained this feature, the ancestors of chimps and humans began to develop bipedality. Some of these bipeds, however, which would include the ancestors of chimps, began to get back down on all fours as their ecology demanded, and whilst they still retained enough of a knuckle-walker's anatomy to not make this prohibitvely unlikely. And it only needed to re-evolve in chimps once, as bonobos\chimp split is post chimp\human split. This could also explain the seeming contradiction of bonobos being better walking than chimps, and more like humans in several ways, if they retained more of the common ancestor traits, while the chimps, growing larger, found knuckle walking like the gorillas a better adaptation. The vestigial bone would make later use of it for the same purpose an easier evolution than evolving a new way to knuckle walk. Like big beaks little beaks on the finches. There was likely a bit of up and down going on due to the climate changes - perhaps the savanah period sent the chimps more to the ground and back to their knuckles? Enjoy. we are limited in our ability to understand
by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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pandion Member (Idle past 3001 days) Posts: 166 From: Houston Joined: |
You seem to have missed the point.
There are less complicated and tortorous routes which would acheive the same thing. So the development of a trait in an ancestor, the loss of that trait in descendants and then the redevelopment in subsequent populations is less complicated and tortuous? Perhaps you just skipped over my first sentence. I said:
quote: What that means is that I believe that knuckle walking was developed in some ancestral ape, retained by gorillas, retained by chimps and bonobos (they diverged after separation from the human lineage). Therefore, that wrist locking mechanism that was retained in Australopithecus afarensis was vestigial, since many other features of anatomy show that A. afarensis was, without question, primarily bipedal. I don't see how it is constructive to pretend that there are other "less tortuous" ways in which 3 species could have an identical mechanism, while only one doesn't have it, while ancestors of that one species retained that mechanism. Does anyone actually believe that knuckle walking was lost and regained by any of the species?
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caffeine Member (Idle past 1025 days) Posts: 1800 From: Prague, Czech Republic Joined: |
So the development of a trait in an ancestor, the loss of that trait in descendants and then the redevelopment in subsequent populations is less complicated and tortuous? Less tortorous than the same trait evolving independently in three separate lineages, yes. The key point being, though, that it doesn't need to be lost and regained in subsequent populations. It need only be lost once, and regained once.
quote: I have no idea; I just don't see grounds for dismissing it as ludicrously improbable. As you've pointed out, at least one of the traits essential for knuckle-walking - the wrist locking mechanism, was retained long after hominids had become fully bipedal, so it's not as if everything had to be re-evolved from scratch. And it's not like lost traits aren't regained in some lineages. To reprint one of RAZD's favourite diagrams:
Here we see 5 different cases of lineages of wingless insects with winged ancestors regaining wings. Lost ancestral features are sometimes regained, so there's nothing ridiculous about the argument a priori. If our molecular dates are right and bipedality precedes the human / chimpanzee split, it's definitely worth considering.
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