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Author Topic:   The Common Ancestor?
Tram law
Member (Idle past 2261 days)
Posts: 283
From: Weed, California, USA
Joined: 08-15-2010


Message 1 of 341 (574743)
08-17-2010 2:42 PM


If there is a common ancestor to both humans and apes, has it been found?

If not, doesn't that call into question the existence of common ancestors?


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Message 2 of 341 (574755)
08-17-2010 4:31 PM


Thread Copied from Proposed New Topics Forum
Thread copied here from the The Common Ancestor? thread in the Proposed New Topics forum.
    
Dr Jack
Member
Posts: 3506
From: Leicester, England
Joined: 07-14-2003


Message 3 of 341 (574756)
08-17-2010 4:36 PM
Reply to: Message 1 by Tram law
08-17-2010 2:42 PM


Humans are apes. And as a matter of fact we've found more than a few organisms linking humans to other apes.

But, leaving that aside, why should it call it into question? Humans aren't special; we're just another species. There's no reason that a human/chimp common ancestor should be considered more important evidence for the ToE than the hippo/whale common ancestor.


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PaulK
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(1)
Message 4 of 341 (574763)
08-17-2010 5:20 PM
Reply to: Message 1 by Tram law
08-17-2010 2:42 PM


Presumably you mean the most recent common ancestor of humans and all modern apes (since the most recent common ancestor would itself be classified as an ape, and since the most recent common ancestor of humans with chimpanzees is more recent than the most recent common ancestor of humans - and chimps - with orangutans).

The answer is that we probably have not found it but there's no way to tell for sure. Most species - especially land vertebrates - have left no fossils whatsoever. And it is impossible to tell for certain whether a fossil actually is in the direct line of ancestry rather than simply an offshoot except in very special cases.

I imagine that you actually want the last common ancestor of humans and chimpanzees. Although there's no fossil I can point to and say that it is that, there is Orrorin tugenensis which likely belongs on the human side of the divide, and dates to shortly after the lineages diverged.

So, we don't have any expectation of finding "the common ancestor". What we expect to find is a sampling of species that includes - maybe - some common ancestors and a lot more near relatives, like Orrorin. And that's what we do find.


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Taq
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Message 5 of 341 (574786)
08-17-2010 8:27 PM
Reply to: Message 1 by Tram law
08-17-2010 2:42 PM


If there is a common ancestor to both humans and apes, has it been found?

If not, doesn't that call into question the existence of common ancestors?

The DNA evidence for a common ancestor is overwhelming (e.g. ERV's). Whether or not we have found a fossil specimen that is our ancestor (which we couldn't determine anyway since it would require a DNA sample) does not refute the DNA evidence.

To use an analogy, imagine a murder trial where the defendant's bloody fingerprints, DNA, and fibers were found at the scene of the crime. Would not finding the defendant's shoe prints refute any of this evidence?


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barbara
Member (Idle past 2358 days)
Posts: 167
Joined: 07-19-2010


Message 6 of 341 (582647)
09-22-2010 1:42 PM
Reply to: Message 5 by Taq
08-17-2010 8:27 PM


Some of the journals that I have read state that humans are 96% the same as in chimps, gorillas, and orangutans. However, I also read that some of the retroviruses sequences are species specific in each one.

The neanderthal DNA also says we are 96% the same. They appear closer to humans then chimps yet the difference is still 4%. These percentages seem to contradict depending on what journal you read so this may not prove anything yet.

There hasn't been any other species between Neanderthal and modern humans is there in the fossil record?


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Coyote
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Message 7 of 341 (582650)
09-22-2010 1:50 PM
Reply to: Message 6 by barbara
09-22-2010 1:42 PM


There hasn't been any other species between Neanderthal and modern humans is there in the fossil record?

Neanderthal and modern humans are on different branches of the tree. They split from one another several hundred thousand years ago.

As such, there could not be a species between the two. There is a common ancestor if you go back to where the branching occurred.


Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.
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Dr Adequate
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Message 8 of 341 (582654)
09-22-2010 2:29 PM
Reply to: Message 6 by barbara
09-22-2010 1:42 PM


The neanderthal DNA also says we are 96% the same. They appear closer to humans then chimps yet the difference is still 4%. These percentages seem to contradict depending on what journal you read ...

The real difference is in what exactly you're counting.

Consider the following two genes (this is a made-up example, all real genes are longer).

ACTCGACGG

ACTTGACGA

How similar are they? If we count base-pairs, 77%. If we count codons, 33%. If we count genes, 0%. If we count proteins, 66%.

So when you see any figure cited, you should ask "percentage of what?" Different people would give different figures when talking about exactly the same data, depending on what exactly it is they're counting. Saying "96% the same" is actually rather meaningless unless you say how you're counting.

This may explain some of the apparent inconsistencies you see when people cite these figures.

There hasn't been any other species between Neanderthal and modern humans is there in the fossil record?

Neanderthals aren't ancestral to modern humans, they're a sister species. We don't expect there to be anything between them.


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Taq
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Posts: 7192
Joined: 03-06-2009
Member Rating: 3.1


Message 9 of 341 (582664)
09-22-2010 4:05 PM
Reply to: Message 6 by barbara
09-22-2010 1:42 PM


Some of the journals that I have read state that humans are 96% the same as in chimps, gorillas, and orangutans.

Like others have stated, it depends on the comparison that you are making, but 96% across the entire Hominidae family is a good approximate number.

However, I also read that some of the retroviruses sequences are species specific in each one.

Yes, there are lineage specific insertions for every ape species, including humans. These are retroviral insertions that occurred since each lineage branched off from the common ancestor. However, we still share the ERV's that were part of the common ancestor's genome.

The neanderthal DNA also says we are 96% the same.

Again, depends on the comparison. If we ignore insertions and deletions of DNA I think the number is closer to 99% at the DNA base level.

There hasn't been any other species between Neanderthal and modern humans is there in the fossil record?

No, just like there isn't any dog variety that is between chihuahuas and great danes. Modern humans and neanderthals were cousins.


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barbara
Member (Idle past 2358 days)
Posts: 167
Joined: 07-19-2010


Message 10 of 341 (582786)
09-23-2010 1:52 PM
Reply to: Message 8 by Dr Adequate
09-22-2010 2:29 PM


Which part is the actual difference?
Do you use base pairs, codons, genes, or proteins to determine what sets us apart from other forms of life?
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AZPaul3
Member
Posts: 3428
From: Phoenix
Joined: 11-06-2006


Message 11 of 341 (582788)
09-23-2010 2:19 PM
Reply to: Message 10 by barbara
09-23-2010 1:52 PM


Re: Which part is the actual difference?
Do you use base pairs, codons, genes, or proteins to determine what sets us apart from other forms of life?

Well, we're not apart from other forms of life, but if we're talking genomic comparisons then any of the above will do, though in most studies the differences cited are in base-pairs.

Edited by AZPaul3, : spelin, as usual.


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barbara
Member (Idle past 2358 days)
Posts: 167
Joined: 07-19-2010


Message 12 of 341 (582794)
09-23-2010 2:54 PM
Reply to: Message 9 by Taq
09-22-2010 4:05 PM


If you ignore insertions and deletions of DNA in all species, would we be 99% the same?
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Taq
Member
Posts: 7192
Joined: 03-06-2009
Member Rating: 3.1


Message 13 of 341 (582823)
09-23-2010 4:07 PM
Reply to: Message 12 by barbara
09-23-2010 2:54 PM


If you ignore insertions and deletions of DNA in all species, would we be 99% the same?

No. The more distant the common ancestor between any two species ther more time there has been for the accumulation of point mutations. There are 3 ways that DNA can be modified (i.e. mutated). They are as follows:


Original DNA:
TTTAAAGGGCCC

Point mutation (a T is changed to a G):
TGTAAAGGGCCC

Insertion (the three C's at the beginning are inserted):
TTTCCCAAAGGGCCC

Deletion (the G's are deleted):
TTTAAACCC

Edited by Taq, : No reason given.


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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


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AZPaul3
Member
Posts: 3428
From: Phoenix
Joined: 11-06-2006


Message 15 of 341 (582857)
09-23-2010 5:21 PM
Reply to: Message 14 by Jon
09-23-2010 5:03 PM


Re: Bad Analogies = Bad Science
There's no such thing as a common ancestor and the whole process of biological evolution precludes such a critter from having existed.

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?

How did we come about? Special creation?

Isn't it true that every living thing has an ancestor from a few generations ago? And that ancestor had an ancestor from a few generations prior to that? How far back do you propose we go before we run out of ancestors? Then what came before that?

I'd bet that if we had the complete genealogies back far enough you and I could find a common ancestor between us. Got any French in your background?

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.

Edited by AZPaul3, : expansion on the theme

Edited by AZPaul3, : Reorder paragraph

Edited by AZPaul3, : correction


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