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Author Topic:   The Common Ancestor?
barbara
Member (Idle past 3030 days)
Posts: 167
Joined: 07-19-2010


Message 61 of 341 (583577)
09-28-2010 1:52 AM
Reply to: Message 34 by Taq
09-24-2010 1:06 PM


Re: Bad Analogies = Bad Science
If we take the human lineage completely out of the picture, how did the chimp, gorilla and orangutan diverge? Did both diverge from one? These 3 live in specific locations so its hard to grasp that they would have cross paths in history.
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Dr Adequate
Member
Posts: 16097
Joined: 07-20-2006


Message 62 of 341 (583585)
09-28-2010 4:04 AM
Reply to: Message 61 by barbara
09-28-2010 1:52 AM


Re: Bad Analogies = Bad Science

|--------------- orangutans
---|
| |----------- gorillas
|---|
| |--- chimps
| |---|
|---| |--- bonobos
|
|------- humans

This message is a reply to:
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Dr Adequate
Member
Posts: 16097
Joined: 07-20-2006


Message 63 of 341 (583586)
09-28-2010 4:22 AM
Reply to: Message 58 by Jon
09-27-2010 10:20 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.

Hold your outrage. It would be remarkable if that individual uniquely held that distinction. It is inevitable that at least one individual did.

In fact, let me blow your mind a little.

There existed a common ancestor of all humans and chimps/bonobos who had two children, one of whom was the common ancestor of all living humans but no chimps/bonobos, and the other of whom was the common ancestor of all living chimps/bonobos but no humans.

Speciation does not show effects in single individuals.

Quite so. And the two children I just mentioned might for all I know have been identical twins.


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Dr Adequate
Member
Posts: 16097
Joined: 07-20-2006


Message 64 of 341 (583588)
09-28-2010 4:27 AM
Reply to: Message 56 by Strongbow
09-27-2010 8:26 PM


Re: SCOTUS Ruling Tactics = Bad Analogies
Common ERV's an excellent way to determine common ancestors ...

Common ancestry.


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Strongbow
Junior Member (Idle past 3138 days)
Posts: 26
Joined: 09-16-2010


Message 65 of 341 (583602)
09-28-2010 7:31 AM
Reply to: Message 59 by Jon
09-27-2010 10:51 PM


Re: SCOTUS Ruling Tactics = Bad Analogies
quote:
Easy. I agree with your statements. I just found your explanation funny.

Roger that... I misinterpreted your reply and misunderstood your postion. My apologies.


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Strongbow
Junior Member (Idle past 3138 days)
Posts: 26
Joined: 09-16-2010


Message 66 of 341 (583603)
09-28-2010 7:39 AM
Reply to: Message 63 by Dr Adequate
09-28-2010 4:22 AM


Re: Ancestor in common; yes.
quote:
There existed a common ancestor of all humans and chimps/bonobos who had two children, one of whom was the common ancestor of all living humans but no chimps/bonobos, and the other of whom was the common ancestor of all living chimps/bonobos but no humans.

OK.... I'm a bit confused.... how do we know that? Why couldn't humans have descended from an individual from one part of the population, and chimps/bonobos descended from an individual in another part of the population?


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Dr Jack
Member (Idle past 333 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 67 of 341 (583605)
09-28-2010 7:43 AM
Reply to: Message 63 by Dr Adequate
09-28-2010 4:22 AM


Re: Ancestor in common; yes.
There existed a common ancestor of all humans and chimps/bonobos who had two children, one of whom was the common ancestor of all living humans but no chimps/bonobos, and the other of whom was the common ancestor of all living chimps/bonobos but no humans.

Are you sure about this? Could we see a proof?


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barbara
Member (Idle past 3030 days)
Posts: 167
Joined: 07-19-2010


Message 68 of 341 (583614)
09-28-2010 9:00 AM
Reply to: Message 62 by Dr Adequate
09-28-2010 4:04 AM


Re: Bad Analogies = Bad Science
Response to diagram on common ancestry. Could you please now add in Australopithecus, Homo habilis, Homo Rudolfensis, Homo Erectus, Homo Ergaster, Homo Heidelbergensis, Homo Neanderthal, Homo Cro-magnom, woodland apes. and then modern humans.

Thanks

Woodland apes are australopithecine which may be the same as australopithecus. My error.

Edited by barbara, : No reason given.

Edited by barbara, : correction


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barbara
Member (Idle past 3030 days)
Posts: 167
Joined: 07-19-2010


Message 69 of 341 (583616)
09-28-2010 9:16 AM
Reply to: Message 64 by Dr Adequate
09-28-2010 4:27 AM


Re: SCOTUS Ruling Tactics = Bad Analogies
I read that the genetic differences between chimps and bonobos is 3% and bonobos are chimps but are separated by boundaries, their social behavior is the complete opposite in that chimps are very aggressive while the bonobos are peaceful.

Another article said that our lineage split at the same time as the chimps did from a common ancestor. The 4% difference between us and chimps seems to put us farther back then chimps and bonobos.


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nwr
Member
Posts: 5586
From: Geneva, Illinois
Joined: 08-08-2005


Message 70 of 341 (583630)
09-28-2010 10:09 AM
Reply to: Message 67 by Dr Jack
09-28-2010 7:43 AM


Re: Ancestor in common; yes.
Mr Jack writes:
Are you sure about this? Could we see a proof?

While I have not fully thought it through, I'm inclined to think that Dr Adequate is correct. This would likely come from graph theory (part of combinatorics, which is a branch of mathematics). The family tree is a directed acyclic graph. Well, things get murky if eukaryotes arose from a symbiotic union of simpler organisms, but you don't have to take things back that far if your concern is with a common ancestor for humans and chimps.
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Blue Jay
Member (Idle past 926 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 71 of 341 (583641)
09-28-2010 10:56 AM
Reply to: Message 68 by barbara
09-28-2010 9:00 AM


Re: Bad Analogies = Bad Science
Hi, Barbara.

barbara writes:

Could you please now add in Australopithecus, Homo habilis, Homo Rudolfensis, Homo Erectus, Homo Ergaster, Homo Heidelbergensis, Homo Neanderthal, Homo Cro-magnom, woodland apes. and then modern humans.

All of those are "humans" on Dr Adequate's diagram (except maybe for "woodland apes": I don't know what "woodland apes" are).


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

Darwin loves you.


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Dr Adequate
Member
Posts: 16097
Joined: 07-20-2006


(1)
Message 72 of 341 (583642)
09-28-2010 10:57 AM
Reply to: Message 67 by Dr Jack
09-28-2010 7:43 AM


Re: Ancestor in common; yes.
Are you sure about this? Could we see a proof?

Hmmph. Actually, I'm having trouble making the last part of the argument truly rigorous.

For now, let's go for a weaker proposition: there was at least one individual having two children one of whom was ancestral to some or all living humans but no chimps/bonobos, and the other of whom was the ancestor of some or all living bonobos/chimps but no humans.

---

Consider humans, chimps, bonobos, the common ancestral species and all the intermediate species. Call this set Z. We can divide set Z into four mutually exclusive sets:

Set O: those with 0 living descendants.

Set H: those with only Human living descendants.

Set C: those with only Chimp/bonobo living descendants.

Set B: those with Both human and chimp/bonobo living descendants.

Set B is non-empty. For suppose otherwise. Then we would have no genetic connection between sets H and C except possibly crosses between them that fell into set O, and so were biological dead-ends. Sets H and C would then be in effect two separate clades running in parallel. But by definition Z contains the common ancestral group of H and C, so this is not possible.

So B has some members.

Not every member of set B can have descendants in B, because there is no-one alive today who is a member of set B. So there must be at least one member of B none of whose descendants are in B. Pick any such member of B and call this member B*.

But there are only two ways to be in set B. One is to have a descendant in set B --- which B* does not do by definition --- and the other is for B* to have at least one child in H and one in C.

This completes the proof.

---

Note that there is no proof or claim of uniqueness of B* and no biological grounds on which we should expect it. But there must be at least one.

---

I thought I had a rigorous proof of my original claim, but it keeps slipping through my fingers at present. In order to get at it this way I should have to show that the children of B* (call them H* and C*) were common ancestors of all living humans and of all living chimps/bonobos respectively, and although this seems very likely, I don't know any more that it can be proved certain even given additional biological considerations such as Dollo's law.

I shall have to think about this.

Edited by Dr Adequate, : No reason given.


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Dr Jack
Member (Idle past 333 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 73 of 341 (583646)
09-28-2010 11:41 AM
Reply to: Message 72 by Dr Adequate
09-28-2010 10:57 AM


Re: Ancestor in common; yes.
Cool, thanks.

Doesn't your stronger claim simply follow from the length of time? I mean the MRCA of humans lived ~3500 years ago - presumably the MRCA for chimps follows a similar time scale.


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Jon
Inactive Member


Message 74 of 341 (583649)
09-28-2010 11:58 AM
Reply to: Message 68 by barbara
09-28-2010 9:00 AM


Re: Bad Analogies = Bad Science
Response to diagram on common ancestry. Could you please now add in Australopithecus, Homo habilis, Homo Rudolfensis, Homo Erectus, Homo Ergaster, Homo Heidelbergensis, Homo Neanderthal, Homo Cro-magnom, woodland apes. and then modern humans.

I don't think that'd be necessary for this discussion. It's well established that the critters you listed did not appear until long after the speciation events.

(BTW: I'm also stumped on the woodland apes reference. I googled them, but the closest thing I could find to a mention was listed as being in a book about human violence.)

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


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


Message 75 of 341 (583653)
09-28-2010 12:08 PM
Reply to: Message 53 by Jon
09-27-2010 7:39 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?

Conceptually, we are looking for the most recent ancestor. In the case of humans and chimps, we are looking for the most recent interbreeding population that contained all of the ancestors of both living humans and living chimps.

This is not to be confused with common ancestry of a single gene. I think this is where the confusion is occuring. It is very probable that the common ancestor of a shared chimp/human gene is much older than the members of the most recent common ancestral population.

What is the agreed-upon most recent common ancestor - using the term cautiously - for humans and chimpanzees?

Without DNA from 5-7 million year old hominid fossils it is impossible to determine.

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).

Then we are only looking at the species that contains the most synapomorphies which still does not guarantee direct ancestry to any living organism, human or chimp. DNA is the only way to establish direct ancestry.


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