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Author Topic:   Evolutionary History of Apes
pandion
Member (Idle past 1335 days)
Posts: 166
From: Houston
Joined: 04-06-2009


Message 16 of 25 (530534)
10-14-2009 12:43 AM


Re: Knuckle walking
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.


Replies to this message:
 Message 20 by caffeine, posted 11-30-2009 9:01 AM pandion has responded

  
Huntard
Member (Idle past 630 days)
Posts: 2870
From: Limburg, The Netherlands
Joined: 09-02-2008


Message 17 of 25 (530542)
10-14-2009 2:57 AM


Ra-aired and online
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 hand
My 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


  
RAZD
Member
Posts: 20322
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.5


Message 18 of 25 (537254)
11-27-2009 11:34 PM


for herebedragons
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:
The new news was A Ramidus evolved in a heavily forested floodplain. What do you think Ramidus was doing to support his family?

Digging up tubers and eating nuts and fruits.

http://www.archaeologyinfo.com/ardipithecusramidus.htm

quote:
CLASSIFICATION

This early fossil hominid was initially placed within the Australopithecus genus, with a new specific epithet - ramidus (from the Afar word "ramid", meaning "root") [White, et al, 1994]. Tim White and associates have subsequently reassigned the hominid to a new genus, noting the apparently extreme dissimilarities between ramidus and all other known Australopithecines. They proposed Ardipithecus (from "ardi", which means "ground" or "floor" in the Afar language) to be the genus [White, et al, 1995].

GEOLOGICAL SETTING

The initial and most extensive publication [White, et al, 1994] concerning Ardipithecus. ramidus specified that 17 hominid fossils had been located by the end of 1993. These specimens were retrieved from a cluster of localities West of the Awash River, within the Afar Depression, Aramis, Ethiopia.

Hominid and associated fossil faunas, including wood, seed and vertebrate specimens, were found entirely within a single interval overlying the basal Gaala Tuff complex, and beneath the Daam Aatu Basaltic Tuff (these volcanic strata have produced dates of 4.389 and 4.388 million years, respectively) [Renne, et al, 1999]. This definitively places all Ardipithecine specimens just shy of 4.4 million years ago.

Additionally, the associated strata were most likely produced within the context of a heavily forested, flood plain environment. Evidence for this conclusion was derived from representative non-human fossil remains, particularly from those species whose present-day analogues are environment-specific.


Living in these kind if areas could just mean that the ground is easier to dig for finding tubers and that there are nut and fruit bearing trees and bushes growing in the fertile soil with a relatively high water table.

Then we have the consideration of anatomy (ibid):

quote:
ANATOMY

A morphological description of the initial, mainly dental, fossil remains of Ardipithecus ramidus was published by White et al, 1994. The physical attributes of this hominid show a range of primitive traits, which are most likely character retentions from the last hominid/chimpanzee ancestor. At the same time, some hominid innovations are equally apparent. The currently known traits of Ardipithecus ramidus, in general, can be placed within two categories: ape-like traits and Australopithecine-like traits.

Much of the dentition is ape-like and this hominid most likely had a significantly different dietary niche than did later hominids. A small canine-incisor to postcanine dental ratio, typical of all other known hominids, is strikingly absent in Ardipithecus ramidus. In addition to the presence of a relatively large anterior dentition, tooth enamel is thin. Though slightly greater than in teeth of modern chimpanzees, enamel thickness of A. ramidus is extremely thin by hominid standards.

Premolar and molar morphology also point to niche affinities with the great ape ancestors. Strong crown asymmetries, in particular enlarged buccal cusps, characterize the upper and lower premolars. Additionally, an ape-like molar shape prevails. The length (in the mesiodistal plane) to breadth (in the buccolingual plane) ratio, which is roughly equal to 1 in later hominids, is much greater in A. ramidus.

Some important derived features, link Ardipithecus ramidus with the Australopithecines. Hominid-like canines are present. These are low, blunt, and less projecting than the canines of all other known apes. Upper and lower incisors are larger than those of the Australopithecines, but are smaller than those of chimpanzees. This character state can thus be considered transitional between apes and Australopithecines. Additionally, the lower molars are broader than those of a comparably-sized ape. This trait, too, approaches the common hominid condition.

Finally, something can be said of the skeletal anatomy and how it relates to the potentiality for bipedalism in A. ramidus. Pieces of the cranial bones that have been recovered, including parts of the temporal and the occipital, strongly indicate an anterior positioned foramen magnum. The fact that the skull of A. ramidus rested atop the vertebral column, rather than in front of it, suggests that if this creature was not bipedal in the modern sense, it at least had key adaptations toward a similar end.

Scanty postcranial remains (most significantly, a partial humerus) indicate that A. ramidus was smaller in size than the mean body size of Australopithecus afarensis. However, this particular estimate falls within the range of variation of A. afarensis.



(edited to remove unrelated material)

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) • • •

Replies to this message:
 Message 19 by herebedragons, posted 11-29-2009 9:06 PM RAZD has acknowledged this reply

  
herebedragons
Member (Idle past 67 days)
Posts: 1513
From: Michigan
Joined: 11-22-2009


Message 19 of 25 (537634)
11-29-2009 9:06 PM
Reply to: Message 18 by RAZD
11-27-2009 11:34 PM


Re: for herebedragons
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?


This message is a reply to:
 Message 18 by RAZD, posted 11-27-2009 11:34 PM RAZD has acknowledged this reply

Replies to this message:
 Message 21 by Briterican, posted 11-30-2009 1:47 PM herebedragons has acknowledged this reply

  
caffeine
Member
Posts: 1728
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 5.7


(1)
Message 20 of 25 (537682)
11-30-2009 9:01 AM
Reply to: Message 16 by pandion
10-14-2009 12:43 AM


Re: Knuckle walking
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.


This message is a reply to:
 Message 16 by pandion, posted 10-14-2009 12:43 AM pandion has responded

Replies to this message:
 Message 23 by RAZD, posted 11-30-2009 8:02 PM caffeine has not yet responded
 Message 24 by pandion, posted 12-01-2009 12:48 AM caffeine has responded

  
Briterican
Member (Idle past 2283 days)
Posts: 340
Joined: 05-29-2008


Message 21 of 25 (537716)
11-30-2009 1:47 PM
Reply to: Message 19 by herebedragons
11-29-2009 9:06 PM


Re: for herebedragons
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).


This message is a reply to:
 Message 19 by herebedragons, posted 11-29-2009 9:06 PM herebedragons has acknowledged this reply

Replies to this message:
 Message 22 by RAZD, posted 11-30-2009 7:54 PM Briterican has not yet responded

  
RAZD
Member
Posts: 20322
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.5


Message 22 of 25 (537769)
11-30-2009 7:54 PM
Reply to: Message 21 by Briterican
11-30-2009 1:47 PM


Re: for herebedragons
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

Briterican
http://www.evcforum.net/cgi-bin/Threads.cgi?action=tml&mb...

herebedragons
http://www.evcforum.net/cgi-bin/Threads.cgi?action=tml&mb...

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.

http://www.evcforum.net/cgi-bin/Threads.cgi?action=tml&mb...

Fav Forums     (% of member's total of 11155)
Coffee House (2431 / 22%)
Biological Evolution (1635 / 15%)
Is It Science? (1088 / 10%)
Intelligent Design ( 778 / 7%)
Dates and Dating ( 585 / 5%)

Of course, that doesn't reflect that the total posts on BioEvo are much greater than the total posts on Dates/ing.

You can also see their recent threads. /offtopic/

Enjoy.


This message is a reply to:
 Message 21 by Briterican, posted 11-30-2009 1:47 PM Briterican has not yet responded

  
RAZD
Member
Posts: 20322
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.5


Message 23 of 25 (537772)
11-30-2009 8:02 PM
Reply to: Message 20 by caffeine
11-30-2009 9:01 AM


Re: Knuckle walking review
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) • • •

This message is a reply to:
 Message 20 by caffeine, posted 11-30-2009 9:01 AM caffeine has not yet responded

  
pandion
Member (Idle past 1335 days)
Posts: 166
From: Houston
Joined: 04-06-2009


Message 24 of 25 (537806)
12-01-2009 12:48 AM
Reply to: Message 20 by caffeine
11-30-2009 9:01 AM


Re: Knuckle walking
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:
I can only conclude that knuckle walking is a derived trait that has been lost in humans and retained in related species.

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?


This message is a reply to:
 Message 20 by caffeine, posted 11-30-2009 9:01 AM caffeine has responded

Replies to this message:
 Message 25 by caffeine, posted 12-01-2009 8:05 AM pandion has not yet responded

  
caffeine
Member
Posts: 1728
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 5.7


Message 25 of 25 (537850)
12-01-2009 8:05 AM
Reply to: Message 24 by pandion
12-01-2009 12:48 AM


Re: Knuckle walking
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:
Does anyone actually believe that knuckle walking was lost and regained by any of the species?

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.


This message is a reply to:
 Message 24 by pandion, posted 12-01-2009 12:48 AM pandion has not yet responded

  
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