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Author Topic:   The Common Ancestor?
Jon
Inactive Member


Message 14 of 341 (582852)
09-23-2010 5:03 PM


Bad Analogies = Bad Science
All this business of common ancestry makes the process look clean and simple. Reality: it's a muddled mess. There's no such thing as a common ancestor and the whole process of biological evolution precludes such a critter from having existed.

It really is too bad when good science gets overrun by grade-school-level analogies.

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


Replies to this message:
 Message 15 by AZPaul3, posted 09-23-2010 5:21 PM Jon has responded
 Message 21 by Blue Jay, posted 09-23-2010 10:44 PM Jon has not yet responded
 Message 27 by Taq, posted 09-24-2010 11:05 AM Jon has not yet responded

  
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:
 Message 17 by AZPaul3, posted 09-23-2010 8:03 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

  
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:
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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

  
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

  
Jon
Inactive Member


Message 31 of 341 (583044)
09-24-2010 12:40 PM
Reply to: Message 28 by AZPaul3
09-24-2010 11:35 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.

When we talk of the evolution of species, direct lineage (which you claim to use synonymously with 'common ancestor') simply does not exist. If this is your understanding of 'common ancestor', then it is flawed. You imply a neatness to the process that it does not merit; decent is messy, hazy, half-assed, and indirect.

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.

This? There are three things being described here—all different, and only the first an example of direct lineage. My grandparents are dead; our ethnicity is tied to an arbitrary regional distinction; miacis is an entire genus. These concepts are related, but not identical. If you think them representative subsets of a single cohesive concept, then describe that concept instead. Trying to get by on poor analogies isn't helping to clarify your position.

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 28 by AZPaul3, posted 09-24-2010 11:35 AM AZPaul3 has responded

Replies to this message:
 Message 35 by AZPaul3, posted 09-24-2010 1:32 PM Jon has not yet responded

  
Jon
Inactive Member


Message 32 of 341 (583048)
09-24-2010 12:50 PM
Reply to: Message 30 by AZPaul3
09-24-2010 12:34 PM


Re: Bad Analogies = Bad Science
Not when the 'common ancestor' being discussed is of the "idealised ... with no further genetic flow" type.

No such thing.

I said that just one sentence after. You're quote-mining now, and misrepresenting my position. I don't do dirty debating.

quote:
Jon in Message 29:
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.

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 30 by AZPaul3, posted 09-24-2010 12:34 PM AZPaul3 has responded

Replies to this message:
 Message 33 by AZPaul3, posted 09-24-2010 1:06 PM Jon has not yet responded

  
Jon
Inactive Member


Message 36 of 341 (583116)
09-24-2010 5:14 PM
Reply to: Message 34 by Taq
09-24-2010 1:06 PM


Re: Bad Analogies = Bad Science
I like your notion of 'common ancestral pool'. I think it more accurately describes what we see in evolution.

But we can still state that ALL members of generation B have ancestors in an earlier generation A, can we not?

Yes, assuming that they do. I'm not attempting to argue against the processes of common decent or human evolution, nor and I trying to undermine the theories that show humans and chimps to be related by these processes. I am merely trying to point out that modern pop-culture anthropology uses terminologies that imply a degree of simplification to these processes that they merely do not exhibit.

I cannot be 100% certain, but I feel you and I are in somewhat of agreement on this issue.

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 34 by Taq, posted 09-24-2010 1:06 PM Taq has not yet responded

  
Jon
Inactive Member


Message 42 of 341 (583455)
09-27-2010 12:05 PM
Reply to: Message 41 by Strongbow
09-27-2010 9:33 AM


Re: Definitions & Feel-good Science
quote:
Generally, the notion is that breeding individuals belong to the same species.

That is on possible definition of species, but not comprehensive, and maybe not even accurate.

I assume you'd agree that Lions and Tigers are separate species, yet Ligers do exist:

http://en.wikipedia.org/wiki/Liger

I can agree, for purposes of discussion that lions and tigers are separate species, but if the scientific evidence says otherwise, then who am I to disagree? There are many instances in the history of science where long-held preconceptions have been thrown out by scientific evidence. Just because we arbitrarily agree to describe and label two things as distinct species does not make them distinct species.

Furthermore, ligers are often sterile, and I must apologize for my forgetful mind, because I neglected to include an important caveat to the general understanding, which is that the offspring must be fertile. Nevertheless, it appears that the occasional liger is fertile, which I must admit is interesting. This pulls us to question our classificatory methods and current classification system.

Before I bring this too far off topic, however, I want to add that these hard-to-tell areas are to be expected given the mussy nature of evolution. Speciation exists on a continuum, where some distinctions are cut and clear and other things are gray. If evolution were cut and clear and species boundaries distinct and precise, then things like the liger would be impossible. This was part of my point early on regarding evolution - it is not only too messy to find the point of common ancestry, but it is too messy for there to even be a point of common ancestry.

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 41 by Strongbow, posted 09-27-2010 9:33 AM Strongbow has not yet responded

Replies to this message:
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Jon
Inactive Member


Message 43 of 341 (583461)
09-27-2010 12:49 PM
Reply to: Message 40 by caffeine
09-27-2010 6:45 AM


Re: Bad Analogies = Bad Science
But this ape also has ancestors. Why stop at the ape? Why not keep going further back?

I'm not sure exactly where the confusion is arising. It seems to me that objections from both you and Jon seem to be based around the idea that saying there are individuals that are common ancestors means this individual must have been seperated from all individuals at the time, and produce two group of offspring which themselves separate off and don't interact.

I have not taken this position. My apologies if my posts implied that I had. If we go really far back, of course we can find a common ancestral species. But we do not want to go that far back, at least I assumed that the OP was not looking for something that far back. My issue was that we cannot get too close (to the time of the split), because the closer we get to the split, the messier things get, and, of course, the point at which the final grouping stopped interbreeding and could thus be categorized as distinct and separated becomes muddled. And not just muddled in that it is difficult to pinpoint the last generation or group of interbreeders, but in that such a point does not exist—there is no such generation.

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 40 by caffeine, posted 09-27-2010 6:45 AM caffeine has acknowledged this reply

Replies to this message:
 Message 44 by barbara, posted 09-27-2010 2:22 PM Jon has not yet responded
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Jon
Inactive Member


Message 52 of 341 (583500)
09-27-2010 6:48 PM
Reply to: Message 45 by Strongbow
09-27-2010 2:31 PM


SCOTUS Ruling Tactics = Bad Analogies
A species is a bit like pornography...

Really? Or are you just saying that because some judge dude did and you thought it'd be cool to repeat?

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 45 by Strongbow, posted 09-27-2010 2:31 PM Strongbow has responded

Replies to this message:
 Message 55 by Strongbow, posted 09-27-2010 8:24 PM Jon has responded

  
Jon
Inactive Member


Message 53 of 341 (583513)
09-27-2010 7:39 PM
Reply to: Message 47 by nwr
09-27-2010 3:10 PM


Re: The most recent common ancestor
Indeed, and it is the time aspect that confuses me. How far back do we go to look for a common ancestor? What is recent? If we go back too far, then we risk getting something that is not representative of the population we want to examine (i.e., something that is not recent enough), but if we get too recent, we risk settling on a critter (since often our understanding of an entire species comes down to the remains of just a couple individuals) that may show a serious degree of interbreeding despite clear differentiations in the gene pools of the two populations - differentiations that clearly indicate a forming difference between the populations, but not one so severe as to prevent breeding.1 What degree of interbreeding and similarities/differences defines our cutoff?

I'm trying to understand how anthropologists decide what is and is not a common ancestor. Are there some critters which lie in a gray area? Perhaps a good way to help would be for an example. What is the agreed-upon most recent common ancestor - using the term cautiously - for humans and chimpanzees? I've seen some names thrown around here, but maybe we can look at the features and characteristics of these ancestors and compare them to present humans and chimps and ancestral humans and chimps to see how the common ancestor relates to both modern populations and to the populations of its daughter species "shortly after the lineages diverged" (to use phrasing by PaulK).

Perhaps answering Tram's question will answer mine.

Jon
__________
1 I, of course, understand the limits on our abilities to examine the DNA of a remain as old as the latest agreed-upon common ancestor.


"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 47 by nwr, posted 09-27-2010 3:10 PM nwr has responded

Replies to this message:
 Message 54 by nwr, posted 09-27-2010 8:18 PM Jon has acknowledged this reply
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Jon
Inactive Member


Message 58 of 341 (583549)
09-27-2010 10:20 PM
Reply to: Message 57 by Ken Fabos
09-27-2010 10:02 PM


Re: Ancestor in common; yes.
Having a specific individual that all our species can count as an ancestor doesn't seem outrageous to me

It seems outrageous to me, and for good reason. Speciation does not show effects in single individuals. It takes an entire population breeding (gene swapping) back and forth generations to bring about changes that create new species out of old ones, and when it does, as the process should tell you, those new traits that can safely be clumped together as characteristics of a new species reside in the population at large, not a specific individual.

evolution within groups isolated by geography and perhaps by territorial behaviour, results in more rapid differentiation than within big populations

Of course this is true, and it is true precisely because evolution works on populations, not individuals.

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 57 by Ken Fabos, posted 09-27-2010 10:02 PM Ken Fabos has not yet responded

Replies to this message:
 Message 63 by Dr Adequate, posted 09-28-2010 4:22 AM Jon has not yet responded

  
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