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Author Topic:   The Common Ancestor?
Jon
Inactive Member


Message 16 of 341 (582897)
09-23-2010 7:49 PM
Reply to: Message 15 by AZPaul3
09-23-2010 5:21 PM


Re: Bad Analogies = Bad Science
You've mentioned at least two different notions for the term 'common ancestor', neither of them the one I, or the OP, intended.

Jon


"Can we say the chair on the cat, for example? Or the basket in the person? No, we can't..." - Harriet J. Ottenheimer

"Dim bulbs save on energy..." - jar


This message is a reply to:
 Message 15 by AZPaul3, posted 09-23-2010 5:21 PM AZPaul3 has responded

Replies to this message:
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AZPaul3
Member
Posts: 4413
From: Phoenix
Joined: 11-06-2006
Member Rating: 3.3


Message 17 of 341 (582900)
09-23-2010 8:03 PM
Reply to: Message 16 by Jon
09-23-2010 7:49 PM


Re: Bad Analogies = Bad Science
OK. So what are these two notions of "common ancestor" I used and how do they differ?

What is this third definition you are using, how does it differ from the one(s) I used and how would anyone have known this difference in context with your message?


This message is a reply to:
 Message 16 by Jon, posted 09-23-2010 7:49 PM Jon has not yet responded

  
Jon
Inactive Member


Message 18 of 341 (582912)
09-23-2010 8:57 PM
Reply to: Message 6 by barbara
09-22-2010 1:42 PM


Definitions & Feel-good Science
There hasn't been any other species between Neanderthal and modern humans is there in the fossil record?

Technically speaking, the remains of Neanderthals and (clearly) modern humans are not fossils, just old bones. Nevertheless, the answer to your question depends on where one wants to put the cut off for 'species'. Generally, the notion is that breeding individuals belong to the same species. With humans, however, this tried-and-true scientific definition is thrown out the window and pop-culture anthropologists simply classify things according to personal tastes.

Unlike what others have posted, it is my firm (evidence-backed) belief that there have been many descended lines from what we can agreeably consider Neanderthal to modern humans. Would I call these descended lines 'other species'? No. But then again, I don't consider Neanderthals and modern humans a separate species.

Jon


"Can we say the chair on the cat, for example? Or the basket in the person? No, we can't..." - Harriet J. Ottenheimer

"Dim bulbs save on energy..." - jar


This message is a reply to:
 Message 6 by barbara, posted 09-22-2010 1:42 PM barbara has not yet responded

Replies to this message:
 Message 19 by AZPaul3, posted 09-23-2010 9:51 PM Jon has responded
 Message 41 by Strongbow, posted 09-27-2010 9:33 AM Jon has responded

  
AZPaul3
Member
Posts: 4413
From: Phoenix
Joined: 11-06-2006
Member Rating: 3.3


Message 19 of 341 (582926)
09-23-2010 9:51 PM
Reply to: Message 18 by Jon
09-23-2010 8:57 PM


Re: Definitions & Feel-good Science
there have been many descended lines from what we can agreeably consider Neanderthal to modern humans.

This is not what the thousands of professional (in your lexicon "pop-culture") anthropologists over the last decades say. And the latest genetic data (2010) says that H. Neanderthalensis was in fact a separate species from H. sapiens.

But this doesn't answer any of my questions about the definition of "common ancestor".

the answer to your question depends on where one wants to put the cut off for 'species'.

Put it where ever you like. My question remains. Was there no "ancestor" three, two, one generation(s) prior to this arbitrary line? If not then where did the first organism after this arbitrary line come from?

None of this obfuscation answers my questions:

What are these two notions of "common ancestor" I used and how do they differ?

What is this third definition you are using, how does it differ from the one(s) I used and how would anyone have known this difference in context with your message?

my firm (evidence-backed) belief that there have been many descended lines from what we can agreeably consider Neanderthal to modern humans.

Let me ask an additional set of questions:

What evidence? Since you disagree with copious amounts of archeological and genetic evidence by thousands of life-long experts over many decades, I assume this is pretty powerful stuff and you have published this evidence somewhere, yes?

Finally, what are your credentials in this field? Or any field?
You do have them, yes? Or are you just full of ...

yourself?


This message is a reply to:
 Message 18 by Jon, posted 09-23-2010 8:57 PM Jon has responded

Replies to this message:
 Message 20 by Jon, posted 09-23-2010 10:34 PM AZPaul3 has responded

  
Jon
Inactive Member


Message 20 of 341 (582937)
09-23-2010 10:34 PM
Reply to: Message 19 by AZPaul3
09-23-2010 9:51 PM


Re: Definitions & Feel-good Science
there have been many descended lines from what we can agreeably consider Neanderthal to modern humans.

This is not what the thousands of professional (in your lexicon "pop-culture") anthropologists over the last decades say. And the latest genetic data (2010) says that H. Neanderthalensis was in fact a separate species from H. sapiens.

My remark on Neanderthals and modern humans was an aside and is off-topic in this thread as it is clearly irrelevant to the time depth in question. If you want to continue on that topic, start a new thread. I'll be happy to meet you there.

But this doesn't answer any of my questions about the definition of "common ancestor".

Good. It wasn't meant to, and would have been off-topic and irrelevant to the post to which I was replying, which was, quite ironically, not the post you made to me. I'm typing these in commercial breaks; when I'm done with the tube, I'll give your question the attention it deserves.

What are these two notions of "common ancestor" I used and how do they differ?

See above.

What is this third definition you are using, how does it differ from the one(s) I used and how would anyone have known this difference in context with your message?

See above.

What evidence? Since you disagree with copious amounts of archeological and genetic evidence by thousands of life-long experts over many decades, I assume this is pretty powerful stuff and you have published this evidence somewhere, yes?

Again, off-topic.

Finally, what are your credentials in this field? Or any field?
You do have them, yes? Or are you just full of ...

Again, off-topic... and highly fallacious reasoning to boot.

Jon


This message is a reply to:
 Message 19 by AZPaul3, posted 09-23-2010 9:51 PM AZPaul3 has responded

Replies to this message:
 Message 22 by AZPaul3, posted 09-24-2010 12:00 AM Jon has not yet responded

  
Blue Jay
Member (Idle past 926 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 21 of 341 (582938)
09-23-2010 10:44 PM
Reply to: Message 14 by Jon
09-23-2010 5:03 PM


Re: Bad Analogies = Bad Science
Hi, Jon.

Jon writes:

There's no such thing as a common ancestor and the whole process of biological evolution precludes such a critter from having existed.

I agree with Paul on this one.

I have never understood the phrase "common ancestor" to refer to a single individual organism, but to a population or species from which two or more distinct evolutionary lineages arose.

In this view (which I think is the typical view in biology), a common ancestor is unavoidable.

I think things get a little muddled when fossil species descriptions are based entirely on only one or two specimens, so the species and the specimen become synonymized in the public mind.


-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.


This message is a reply to:
 Message 14 by Jon, posted 09-23-2010 5:03 PM Jon has not yet responded

Replies to this message:
 Message 23 by caffeine, posted 09-24-2010 4:39 AM Blue Jay has responded

  
AZPaul3
Member
Posts: 4413
From: Phoenix
Joined: 11-06-2006
Member Rating: 3.3


Message 22 of 341 (582945)
09-24-2010 12:00 AM
Reply to: Message 20 by Jon
09-23-2010 10:34 PM


Re: Definitions & Feel-good Science
I'll give your question the attention it deserves.

No, don't bother, Jon.

I think I have the answers to my last set of questions.


This message is a reply to:
 Message 20 by Jon, posted 09-23-2010 10:34 PM Jon has not yet responded

  
caffeine
Member
Posts: 1682
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 2.6


Message 23 of 341 (582985)
09-24-2010 4:39 AM
Reply to: Message 21 by Blue Jay
09-23-2010 10:44 PM


Re: Bad Analogies = Bad Science
I have never understood the phrase "common ancestor" to refer to a single individual organism, but to a population or species from which two or more distinct evolutionary lineages arose.

In this view (which I think is the typical view in biology), a common ancestor is unavoidable.

Surely, even if 'common ancestor' is taken to refer to a single individual, it's still a logical necessity for everything to have a common ancestor with everything else (assuming common descent). There wouldn't be a unique individual, and we could never hope to find or know if we've found such an individual, but how could they not exist?


This message is a reply to:
 Message 21 by Blue Jay, posted 09-23-2010 10:44 PM Blue Jay has responded

Replies to this message:
 Message 25 by Jon, posted 09-24-2010 10:24 AM caffeine has responded
 Message 37 by Blue Jay, posted 09-25-2010 3:04 PM caffeine has responded

  
Jon
Inactive Member


Message 24 of 341 (583009)
09-24-2010 9:39 AM
Reply to: Message 15 by AZPaul3
09-23-2010 5:21 PM


Re: Bad Analogies = Bad Science
Oh. So you saying that my cousin in Massachusetts, My cousin in Florida and I do NOT have a common ancestor in Grandad?

So if common ancestors do not exist who was Grandad?

This is a different type of 'common ancestor'.

quote:
Bluejay in Message 21:
I have never understood the phrase "common ancestor" to refer to a single individual organism...

Your grandfather—being a single individual—is not the same notion of 'common ancestor' used in evolution. Unless you, your cousins, your sisters, and your brothers have all been busy procreating with one another, your analogy is a flawed oversimplification.

So show me how the the Miacis line did not radiate into ursine, canine and feline lineages and is thus NOT the common ancestor for these groups.

Again, you're missing the mark. I highly doubt Tram was hoping for an answer so vague that it only described the genus. Here, instead of being too precise ('common ancestor' = single individual), you're too broad ('common ancestor' = entire genus); what's even worse is that you've added a second notion to the term you previously discussed, thus making its specific intended notion unclear, ambiguous, and thus confusing.

So as I said, bad analogies equate to bad science.

Jon

Edited by Jon, : Bad spelling = Bad posts


"Can we say the chair on the cat, for example? Or the basket in the person? No, we can't..." - Harriet J. Ottenheimer

"Dim bulbs save on energy..." - jar


This message is a reply to:
 Message 15 by AZPaul3, posted 09-23-2010 5:21 PM AZPaul3 has responded

Replies to this message:
 Message 28 by AZPaul3, posted 09-24-2010 11:35 AM Jon has responded

  
Jon
Inactive Member


Message 25 of 341 (583015)
09-24-2010 10:24 AM
Reply to: Message 23 by caffeine
09-24-2010 4:39 AM


Re: Bad Analogies = Bad Science
There wouldn't be a unique individual, and we could never hope to find or know if we've found such an individual...

Good. What's more, to be sure we've found a 'common ancestor', we may have to go back much further than we'd like. There is nothing about the theory of evolution that should make us believe that of a sudden two lineages ceased interbreeding and so were thus instantly distinct species, with the parents of those lineages being considered representatives of the 'common ancestor'.

I think it would be difficult, in fact, impossible, to find and pinpoint one species, one subset, or even a single generation that was clearly the last to link to both prehistoric humans and prehistoric chimps. I attribute this difficulty to the fact that clear-cut species boundaries are not possible. It is easy to look at generation Y and then compare it to generation D several million years earlier and say "yeah, shit, I suppose they aren't the same species"; but the closer the generations you are trying to compare become, the more difficult it gets trying to sift them into different species. Indeed, there is never going to be a single identifiable moment when one generation from one lineage ceased breeding with members of another lineage from the same generation. We can find several generations that we perceive as being involved in the 'split', and some individuals generally characteristic of those involved in the split, but we're over-exaggerating our abilities if we hope to find the single variety representative of the pre-split generation; the best understanding we can hope for is a general one.

... how could they not exist?

Evolution is not a linear process. The better question, then, is how would we know when we found it?

Jon

Edited by Jon, : Elaboration.


"Can we say the chair on the cat, for example? Or the basket in the person? No, we can't..." - Harriet J. Ottenheimer

"Dim bulbs save on energy..." - jar


This message is a reply to:
 Message 23 by caffeine, posted 09-24-2010 4:39 AM caffeine has responded

Replies to this message:
 Message 26 by caffeine, posted 09-24-2010 10:51 AM Jon has responded

  
caffeine
Member
Posts: 1682
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 2.6


Message 26 of 341 (583028)
09-24-2010 10:51 AM
Reply to: Message 25 by Jon
09-24-2010 10:24 AM


Re: Bad Analogies = Bad Science
Evolution is not a linear process. The better question, then, is how would we know when we found it?

As I noted above, we couldn't. From what you've said here, I don't think you disagree with anyone except the OP, which seemed to imply we should be looking for one specific species (or individual) that confirms the common ancestor.

However, it's still clear that evolutionary theory requires common ancestors rather than precluding them, as you said in Message 14. I understand that you're making the point that it would never be practically possible to identify a 'last common ancestor', and that species divisions are going to be messy and rarely conform to the idealised case of siblings swept to different islands to establish founder populations, with no further genetic flow. It's confusing and misleading to say this means there are no common ancestors, however.


This message is a reply to:
 Message 25 by Jon, posted 09-24-2010 10:24 AM Jon has responded

Replies to this message:
 Message 29 by Jon, posted 09-24-2010 11:59 AM caffeine has not yet responded

  
Taq
Member
Posts: 7997
Joined: 03-06-2009
Member Rating: 3.8


Message 27 of 341 (583031)
09-24-2010 11:05 AM
Reply to: Message 14 by Jon
09-23-2010 5:03 PM


Re: Bad Analogies = Bad Science
All this business of common ancestry makes the process look clean and simple. Reality: it's a muddled mess.

Just about every concept in biology is plagued by the same problem. As I often like to say, biology is messy.

But as you say in a subsequent post, if we jump through time in bigger jumps it is obvious. At one point there is an interbreeding population. When we come back at a much later time there are now two populations that do not interbreed with all members in both populations being able to trace their lineages back to members of that past population.

To use another analogy, there is no obvious demarcation between tall and short but all of us can agree that Danny DeVito is short and Shaquille O'Neal is tall. Taxonomy, the definition of species, and the very process of speciation are plagued by the same problems. With very fine resolution it is really hard to tease out the differences, but with the long lens of time we can see the obvious trends.


This message is a reply to:
 Message 14 by Jon, posted 09-23-2010 5:03 PM Jon has not yet responded

  
AZPaul3
Member
Posts: 4413
From: Phoenix
Joined: 11-06-2006
Member Rating: 3.3


Message 28 of 341 (583035)
09-24-2010 11:35 AM
Reply to: Message 24 by Jon
09-24-2010 9:39 AM


Re: Bad Definition = Bad Argument
First of all, Jon, "common ancestor" is not an analogy for some other concept. It is the direct concept itself. The concept of direct lineage.

Second, in the case of my family, we have a direct demonstrable link between the various later individuals and a single specific earlier individual from which we stem. That is our common ancestor.

Third, as we proceed deeper into time the specific information of exact genealogy, between say you and I, may be lost and the best we could hope for is to identify a population subset from which we both stem. European? French? Mediterranean coast? Marseille region? The "common ancestor" concept is as valid and meaningful in this instance as in the above and is not analogous to any other concept but is a concept of direct lineage, though, in this case, can only get as specific as to identify a sub-population, a founder population, of common origin.

When we get to bears, cats and dogs we find that the best we can get, the last direct link between these that can be identified, is not an individual or even as fine as a sub-population, but the more granular overall population of an early carnivore we call miacis about 60 million years ago. The concept still holds and is valid. Miacis is the founder population, the earliest "common ancestor," to these lineages.

This is the standard definition of "common ancestor" used in the field.

So what is your definition of "common ancestor"? And why would you choose a definition totally at odds with the standard in the field?

Are you trying to deny nested hierarchy, common descent?

Bad definition = bad argument

Edited by AZPaul3, : edits


This message is a reply to:
 Message 24 by Jon, posted 09-24-2010 9:39 AM Jon has responded

Replies to this message:
 Message 31 by Jon, posted 09-24-2010 12:40 PM AZPaul3 has responded

  
Jon
Inactive Member


Message 29 of 341 (583039)
09-24-2010 11:59 AM
Reply to: Message 26 by caffeine
09-24-2010 10:51 AM


Re: Bad Analogies = Bad Science
However, it's still clear that evolutionary theory requires common ancestors rather than precluding them, as you said in Message 14. (Link added)

I think every time we go back we're going to undoubtedly find input again from even earlier generations, requiring that we go back to that generation as the 'common ancestor'. But even this generation will have input from earlier ones, requiring that we again step back further in time. We could go on forever until we reach the first life form, but this will hardly advance our understanding of the evolution of any particular species. We, instead, have to eventually decide a cutoff, but doing so requires us to admit that our cutoff point is somewhat arbitrary and not necessarily representative of a true genetic and breeding relationship between the beasts in question.

It's confusing and misleading to say this means there are no common ancestors, however

Not when the 'common ancestor' being discussed is of the "idealised ... with no further genetic flow" type. When this is the meaning folk begin putting on to the term, it becomes necessary to point out that their notion of 'common ancestor' is a fantasized non-existent entity/species/generation. In pop-culture anthropology, this is the meaning often ascribed to the term, unfortunately, and the meaning that I saw being used in this thread.

In the sense that everything has a parent, however, I agree that there clearly have to be common parents; I just think it faulty to believe that there could be common parents to an entire species. Seems too Adam and Eve to me, even if we are talking about an entire generation of parents, rather than just two people.

Jon


"Can we say the chair on the cat, for example? Or the basket in the person? No, we can't..." - Harriet J. Ottenheimer

"Dim bulbs save on energy..." - jar


This message is a reply to:
 Message 26 by caffeine, posted 09-24-2010 10:51 AM caffeine has not yet responded

Replies to this message:
 Message 30 by AZPaul3, posted 09-24-2010 12:34 PM Jon has responded
 Message 34 by Taq, posted 09-24-2010 1:06 PM Jon has responded

  
AZPaul3
Member
Posts: 4413
From: Phoenix
Joined: 11-06-2006
Member Rating: 3.3


Message 30 of 341 (583043)
09-24-2010 12:34 PM
Reply to: Message 29 by Jon
09-24-2010 11:59 AM


Re: Bad Analogies = Bad Science
We, instead, have to eventually decide a cutoff, but doing so requires us to admit that our cutoff point is somewhat arbitrary and not necessarily representative of a true genetic and breeding relationship between the beasts in question.

What are you talking about? If this is your view of the use of "common ancestor" in the field it is a bad one.

Take any two species. Trace their lineages back to the species or genus where those lineages converge and, by definition, you have found the earliest common ancestor between the two. And, yes, this does indeed show the "true genetic and breeding relationship between the beasts in question."

Not when the 'common ancestor' being discussed is of the "idealised ... with no further genetic flow" type.

No such thing. This "definition" of "common ancestor" is strictly within your own head and is fallacious.

I just think it faulty to believe that there could be common parents to an entire species. Seems too Adam and Eve to me, even if we are talking about an entire generation of parents, rather than just two people.

Then stop thinking like that. This is not what the definition of "common ancestor" entails.


This message is a reply to:
 Message 29 by Jon, posted 09-24-2010 11:59 AM Jon has responded

Replies to this message:
 Message 32 by Jon, posted 09-24-2010 12:50 PM AZPaul3 has responded

  
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