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Author Topic:   Rate of Genetic Change
Percy
Member
Posts: 18309
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.7


Message 1 of 5 (86)
01-21-2001 10:50 AM


This is a reply to Message 6652 at Yahoo's message board for the club.

quote:
Originally posted by fasstedddy:
In other words, the explanation states there was adequate time for mutations to have produced the changes supposedly found in the fossil record, therefore the fossil record is explained as the result of the effect these mutations had on speciation verified by our time calculations. That is far from being persuasive. Benny could just as well be at Yellowstone Park.

Henry Gee has just written an excellent book on just this question called In Search of Deep Time. At great length and detail (some might say greatly repetitive length and detail) he makes the point that in deep time (the full scope of time back to the origin of life on earth) there is no way to know with any certainty how any fossil relates to life-forms today. He claims that most information necessary to making such connections is now gone, having been eaten, buried, crushed, decayed, subducted, eroded and so forth. He says with fair certainty that most of life's history is forever unavailable to us, either no longer existent or so deeply buried as to have the same result.

Paleontology is the weak science of biology, but it has by far the biggest cachet, with dinosaur fossil reconstructions the centerpiece and human origins the most significant sideshow. It also has had the advantage of featuring some of biology's most interesting personalities, from Cope and Marsh's dinosaur fossil wars of the late 1800s to the modern personages of Colin Patterson, Louis Leaky, son Richard Leaky, Donald Johanson, Stephen Jay Gould, Robert Bakker and Paul Sereno. All have given in to the temptation of speculating on the relationship of ancient fossils to modern life, and some have fallen over into the mistake of thinking that the speculation is in some way conclusive.

The ephemeral nature of these speculations is obvious to anyone who has read Richard Leaky's books. Son of the once much more famous Louis Leaky he has become a respected paleo-anthropologist in his own right, but he has also been at the center of a virulent debate on human origins. After changing his mind many times on which fossil hominid remains lay on a direct line to modern humans he has lately become more philosophical. His books are the record of the changeable nature of such speculations. It seems that for him each new fossil discovery changes everything, and he is by no means alone in this. I use Richard Leaky only as an example of an inclination rampant in paleontological circles.

Henry Gee has his own axe to grind. As a cladist (One who organizes things into categories, or clades, according to shared characteristics. A short note on pronounciation: the a in cladist and cladistics is short, while the a in clade is long.) he may feel a bit ignored since they receive far less attention than paleontologists more willing to walk out on slender limbs (that they often themselves saw off). He makes his point a bit stridently, though patiently, clearly and very repetitively. The point is that given the vastness of deep time there is no way to know if any particular fossil lies on a direct evolutionary path to any modern life-forms, including us, or how it is connected to other fossils of any age. The cladists, he claims, are the only group willing to acknowledge what is inherently unknowable and limit themselves to dealing with what is realistically knowable. That means looking at specific characteristics in great detail and classifying fossils according to degree of similarity into clades.

The bottom line is that Henry Gee and the cladists agree with you. Just because sufficient time has elapsed for a fossil life-form to have evolved into another suggested life-form (fossil or modern it doesn't matter) does not mean that it did. Any speculation is just that, mere speculation.

Where you and Gee may part company is in the conclusion. I may have read an insufficient number of your posts to have formed a clear idea of your position, but I will guess that you do not accept evolution. But to concede that the evidence necessary to any particular evolutionary conclusion does not exist is not the same thing as conceding that evolution itself does not exist. Gee believes that in most cases the evidence to demonstrate specific evolutionary pathways is absent, but fully accepts the theory of evolution, and is using his chosen science of cladistics to understand evolutionary relationships to the limits he believes possible.

Gee's book was a fortunate find for me, for he gives voice to this issue that had been nagging at me for some time. Long-time participants at the Yahoo club may have noticed that whenever the discussion turned to human origins I suddenly went quiet (many probably thought this a good thing ). The reason was that though I could clearly see that, for example, Australopithecus afarensis shared many characteristics with modern humans, I couldn't see how one could on this basis conclude it was a human predecessor. To me it may or may not have lain on a direct path to us, but how could anyone know? Where was the additional evidence necessary for establishing that path? Conclusions seemed premature, yet great paleontological minds had issued tons of conclusions. My resulting confusions precluded my participation on this issue.

But Gee has now made sense of the issues for me and enabled me to take a clear position. We cannot establish with any confidence most evolutionary pathways. The evidence is simply not there. But this fact has no negative impact on the theory of evolution itself.

--Percy

[This message has been edited by Percipient (edited 01-21-2001).]


Replies to this message:
 Message 2 by gene90, posted 01-21-2001 7:07 PM Percy has not yet responded
 Message 3 by lbhandli, posted 01-21-2001 7:28 PM Percy has not yet responded

  
gene90
Member (Idle past 1900 days)
Posts: 1610
Joined: 12-25-2000


Message 2 of 5 (89)
01-21-2001 7:07 PM
Reply to: Message 1 by Percy
01-21-2001 10:50 AM


I do not understand how rate of mutation can establish a time-scale, when natural selection and random trends establish whether a mutation is culled or propagated.
This message is a reply to:
 Message 1 by Percy, posted 01-21-2001 10:50 AM Percy has not yet responded

Replies to this message:
 Message 4 by lbhandli, posted 01-21-2001 7:31 PM gene90 has not yet responded

lbhandli
Inactive Member


Message 3 of 5 (90)
01-21-2001 7:28 PM
Reply to: Message 1 by Percy
01-21-2001 10:50 AM


quote:
Originally posted by Percipient:
Henry Gee has his own axe to grind. As a cladist (One who organizes things into categories, or clades, according to shared characteristics. A short note on pronounciation: the a in cladist and cladistics is short, while the a in clade is long.) he may feel a bit ignored since they receive far less attention than paleontologists more willing to walk out on slender limbs (that they often themselves saw off). He makes his point a bit stridently, though patiently, clearly and very repetitively. The point is that given the vastness of deep time there is no way to know if any particular fossil lies on a direct evolutionary path to any modern life-forms, including us, or how it is connected to other fossils of any age. The cladists, he claims, are the only group willing to acknowledge what is inherently unknowable and limit themselves to dealing with what is realistically knowable. That means looking at specific characteristics in great detail and classifying fossils according to degree of similarity into clades.

The bottom line is that Henry Gee and the cladists agree with you. Just because sufficient time has elapsed for a fossil life-form to have evolved into another suggested life-form (fossil or modern it doesn't matter) does not mean that it did. Any speculation is just that, mere speculation.


That is an excellent point. The key the 29 lines of evidence as I see them is that this is one aspect that could be falsified. If we noted that genetic rates of change change do not meet the required time for changes that are likely, it would cause us to seriously question our understanding of the genetic behind evolution.

The importance of a finding that is consistent with the best evidence we have--and much of that post is based on genetics as well--is that such a rate is predicted from the best evidence and the prediction is met. Standing alone this certainly wouldn't provide enough evidence to accept evolution, but the 29 lines taken as a whole provide a very strong and testable theory that is confirmed by the best evidence we have.

quote:

Where you and Gee may part company is in the conclusion. I may have read an insufficient number of your posts to have formed a clear idea of your position, but I will guess that you do not accept evolution. But to concede that the evidence necessary to any particular evolutionary conclusion does not exist is not the same thing as conceding that evolution itself does not exist. Gee believes that in most cases the evidence to demonstrate specific evolutionary pathways is absent, but fully accepts the theory of evolution, and is using his chosen science of cladistics to understand evolutionary relationships to the limits he believes possible.

Gee's book was a fortunate find for me, for he gives voice to this issue that had been nagging at me for some time. Long-time participants at the Yahoo club may have noticed that whenever the discussion turned to human origins I suddenly went quiet (many probably thought this a good thing

). The reason was that though I could clearly see that, for example, Australopithecus afarensis shared many characteristics with modern humans, I couldn't see how one could on this basis conclude it was a human predecessor. To me it may or may not have lain on a direct path to us, but how could anyone know? Where was the additional evidence necessary for establishing that path? Conclusions seemed premature, yet great paleontological minds had issued tons of conclusions. My resulting confusions precluded my participation on this issue.


And thmsberry quite a while ago, and perhaps in a different thread, pointed this out in a thread I was in. It was a very good point. Lucy, I believe was the example, is almost certainly related to modern humans, but may not be in the lineage. She may have been a cousin as neanderthals are. And this lineage problem is most often unanswerable unless we are able to compare DNA evidence and then that may be inconclusive.

quote:

But Gee has now made sense of the issues for me and enabled me to take a clear position. We cannot establish with any confidence most evolutionary pathways. The evidence is simply not there. But this fact has no negative impact on the theory of evolution itself.


This is interesting. I think it is qualitatively different than thmsberry's position, leaving Fasteddy out here for a second. Thmsberry seems to be arguing that we cannot show relatedness over the family groupings. While we may not make definite linneage lines in most cases, we are able to show general lines from the nested hierarchies we observe. And I would argue that one nested hierarchy being based on fossils would be somewhat questionable in being the lynchpin--however, the matching nested hierarchies provide us with confirmation of the relatedness of different families. And additionally, the best evidence we have demonstrates the chronology of such appearances matching each other which again is not single point to rest the theory on, but provides excellent corroboration. The specific lines may be wrong, but the general progression is still accurate.

Thanks for the post---it was a very informative and thought provoking.

Larry

[This message has been edited by Percipient (edited 01-22-2001).]

Edited by Adminnemooseus, : Fixed coding - b coding was inside quote coding at beginning and outside at ends.


This message is a reply to:
 Message 1 by Percy, posted 01-21-2001 10:50 AM Percy has not yet responded

Replies to this message:
 Message 5 by gene90, posted 01-22-2001 10:18 PM lbhandli has not yet responded

lbhandli
Inactive Member


Message 4 of 5 (91)
01-21-2001 7:31 PM
Reply to: Message 2 by gene90
01-21-2001 7:07 PM


gene: I do not understand how rate of mutation can establish a time-scale, when natural selection and random trends establish whether a mutation is culled or propagated.

It isn't establishing a time scale actually. It is demonstrating that the rate of genetic change we observe today is consistent with the approximate change we observe between diverging species. So, in the example, human and chimp divergence is estimated based on other evidence and then the differences in the genomes are compared to the observed rate of change (including selection) and determined whether on not the rate is plausible for that difference.

HTH
Larry


This message is a reply to:
 Message 2 by gene90, posted 01-21-2001 7:07 PM gene90 has not yet responded

gene90
Member (Idle past 1900 days)
Posts: 1610
Joined: 12-25-2000


Message 5 of 5 (92)
01-22-2001 10:18 PM
Reply to: Message 3 by lbhandli
01-21-2001 7:28 PM


Thanks Larry. I don't think I understand the concept well but it is much less foggy now.
This message is a reply to:
 Message 3 by lbhandli, posted 01-21-2001 7:28 PM lbhandli has not yet responded

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