Universal common ancestry

[Paul C. Anagnostopoulos]

Here is the abstract of a paper by Douglas Theobald in which he uses model selection theory to find support for universal common ancestry. Pretty cool.

http://www.nature.com/nature/journal/v465/n7295/full/nature09014.html#B16

~~ Paul

 

[Wowbagger]

Just another line of investigation, in support of the theory, to throw on top of the pile.

 

[Paul C. Anagnostopoulos]

Indeed. This one attacks the entire tree of life while investigating the question of common ancestry, so that's neat.

~~ Paul

 

[John Hewitt]

Well, I took a look at the abstract, the body text is hidden behind Nature's publication policy, and I am unable to discern what they have done. I do not understand

1. The basis on which these conclusions have been drawn.
2. The significance of the UCA hypothesis.

Could someone briefly explain?

 

[TraneWreck]

Well, I took a look at the abstract, the body text is hidden behind Nature's publication policy, and I am unable to discern what they have done. I do not understand

1. The basis on which these conclusions have been drawn.
2. The significance of the UCA hypothesis.

Could someone briefly explain?

Here's a solid explanation from PZ Myers' page:

http://scienceblogs.com/pharyngula/2010/05/now_weve_got_some_big_numbers.php

 

[John Hewitt]

Here's a solid explanation from PZ Myers' page:

http://scienceblogs.com/pharyngula/2010/05/now_weve_got_some_big_numbers.php

Thank you for that, it does clarify what Theobald has been doing. It does seem to me that his conclusions might be less clear than most observers seem to think. Theobald seems to have selected a set of genes from different organisms, each of whose proteins is performing the same function in those organisms. Would he not, then, expect to find a high degree of relatedness without the assumption of a common ancestor?

In addition, I remain unclear as to why the UCA assumption is perceived as a bedrock to evolution.

 

[Puppycow]

Interesting. I'll probably never be able to understand the math myself though.

IIRC they were getting closer to figuring out what that first critter was and how it happened. Any more news on that front?

 

[Paul C. Anagnostopoulos]

Theobald seems to have selected a set of genes from different organisms, each of whose proteins is performing the same function in those organisms. Would he not, then, expect to find a high degree of relatedness without the assumption of a common ancestor?

What do you mean by "relatedness" vs. "common ancestor"?

What he's done is to try fitting a bunch of explanatory models to the data. These include universal common ancestor, multiple common ancestors, horizontal gene transfer, and various combinations thereof. The universal common ancestor model fits best. There was no assumption of a specific organization of common ancestor(s).

One limitation is that he only considered the three big domains, so viruses are not included.

~~ Paul

 

[Wowbagger]

I remain unclear as to why the UCA assumption is perceived as a bedrock to evolution.

The theory implies that we would expect there to have been one UCA, or at most, a small number of them.

It's not really a "bedrock" of evolution, though. The general process of natural selection seems to work, independently of their being a single UCA or not.

If it turns out that there was lots of evidence for lots of "starting points" for the beginnings of life on Earth, the theory would have to be modified, but its usefulness to scientific investigation would go on in that new form.

In this case, it seems more likely that there was a single UCA. It's not ultimately conclusive, but nothing in science ever is, anyway.

 

[This is The End]

This thread made me remember a (surprisingly old) March 2009 article from Discover magazine about Haplogroup mapping.

I can't find it on their website, so I scanned the appropriate map/chart which depicts the various routes taken as human races branched off.

The interesting part of the sidebar being (not sure if it can be read in the pic):

...DNA studies show we all share a common female ancestor who lived in Africa about 140,000 years ago. In addition, all living men share a common male ancestor who lived in Africa about 60,000 years ago.

Another interesting quote from the main article:

Human races are evolving away from each other. We are getting less alike, not merging into a single mixed humanity.

 

[Humanzee]

tyvm Onlytellsthetruth.

 

[John Hewitt]

The theory implies that we would expect there to have been one UCA, or at most, a small number of them.

It's not really a "bedrock" of evolution, though. The general process of natural selection seems to work, independently of their being a single UCA or not.

If it turns out that there was lots of evidence for lots of "starting points" for the beginnings of life on Earth, the theory would have to be modified, but its usefulness to scientific investigation would go on in that new form.

In this case, it seems more likely that there was a single UCA. It's not ultimately conclusive, but nothing in science ever is, anyway.

I agree with your general sentiments but I don't know of any real evidence for any single UCA and I don't think the paper that began this thread changes things. What there is, in several instances, is evidence for evolution reaching nexi, or nexuses or whatever. OnlyTellsTruth's chart shows some of the evidence for a nexus in human origins occurring when we left Africa, with consequential divergence of human populations throughout the non-African world in a tree structure.

The Cambrian explosion seems to have followed a time when the emergence of multicellular animals created a nexus that allowed those creatures to diverge in a tree structure. The various mass extinctions created the opportunity for the survivors to diverge in their own tree structures etc.

To me, this paper merely suggests some previous nexus leading to some earlier divergence but that is simply what one would expect. It is certainly not the imagery conjured up by the term UCA. I am also left wondering what all the fuss is about with this paper.

 

[Paul C. Anagnostopoulos]

To me, this paper merely suggests some previous nexus leading to some earlier divergence but that is simply what one would expect. It is certainly not the imagery conjured up by the term UCA. I am also left wondering what all the fuss is about with this paper.

It suggests that there was an original nexus from which all forms of extrant life diverged. Why would we expect that to be the case? Life could have popped up independently two or three times.

~~ Paul

 

[Michael Redman]

In addition, all living men share a common male ancestor who lived in Africa about 60,000 years ago.

All living men? How would it be possible for all living men to share an ancestor that all living women did not also share?

 

[Cuddles]

All living men? How would it be possible for all living men to share an ancestor that all living women did not also share?

http://www.planet-science.com/about_sy/events/pdfs/Steve_Jones_Transcript.pdf

It's basically due to the difference in reproductive systems. Men can spread their sperm around all over the place, which tends to result in a few powerful men having lots of children, while the less powerful have significantly fewer. That's not possible for women because of the whole pregnancy thing, so the distribution of children tends to be more spread out across many women.

If you look at this diagram (from here), it shows how the idea of the most recent male or female ancestor can be constructed. That picture shows for women, but if you do the same for men, there will tend to be more than just two or three children at each point, and so it will converge back to the common ancestor much more quickly.

The important point to remember is that this does not say that there were no other people alive at the time, or that this is the ultimate ancestor, both of which are obviously inconsistent with the male and female one occurring at different times. Instead, it is simply the most recent ancestor that all men or women share. Lots of people will also share many ancestors from both earlier and later, and some of the earlier ones will also be common to everyone.

 

[LarianLeQuella]

It suggests that there was an original nexus from which all forms of extrant life diverged. Why would we expect that to be the case? Life could have popped up independently two or three times.

~~ Paul

Very true, and depending on what we learn about abiogenesis, could have some interesting follow up on this. As for there being one UCA for life on earth, think of it in terms of evolution. Our type of life was just more successful than any other theroretical lifeforms that may have started. We wiped them out and took over all the niches.

 

[Michael Redman]

http://www.planet-science.com/about_sy/events/pdfs/Steve_Jones_Transcript.pdf

It's basically due to the difference in reproductive systems. Men can spread their sperm around all over the place, which tends to result in a few powerful men having lots of children, while the less powerful have significantly fewer. That's not possible for women because of the whole pregnancy thing, so the distribution of children tends to be more spread out across many women.

If you look at this diagram (from here), it shows how the idea of the most recent male or female ancestor can be constructed. That picture shows for women, but if you do the same for men, there will tend to be more than just two or three children at each point, and so it will converge back to the common ancestor much more quickly.

The important point to remember is that this does not say that there were no other people alive at the time, or that this is the ultimate ancestor, both of which are obviously inconsistent with the male and female one occurring at different times. Instead, it is simply the most recent ancestor that all men or women share. Lots of people will also share many ancestors from both earlier and later, and some of the earlier ones will also be common to everyone.

That doesn't explain how a man can have an ancestor that is not his daughter's ancestor as well.

 

[Wowbagger]

To me, this paper merely suggests some previous nexus leading to some earlier divergence but that is simply what one would expect. It is certainly not the imagery conjured up by the term UCA. I am also left wondering what all the fuss is about with this paper.

I think that, for most practial purposes, "UCA" and "earliest nexus" essentially mean the same thing.

 

[Eos of the Eons]

All living men? How would it be possible for all living men to share an ancestor that all living women did not also share?

Learn genetics, and how genes can be passed to one gender and not another. I'm guessing here, based on my own limited knowledge of genetics.

 

[Michael Redman]

Learn genetics, and how genes can be passed to one gender and not another. I'm guessing here, based on my own limited knowledge of genetics.

A female has every ancestor that her father has regardless of what genes she inherits.

If the sentence I originally quoted was trying to make the claim that every man alive today possess a gene or genes that he inherited from a common ancestor, it failed to articulate that. It simply says they have a common male ancestor. I'm just pointing out that if every man alive today has one male ancestor in common, then every female alive today must also have that same ancestor in common, even if the women didn't inherit the genes used to demonstrate this common ancestor in men.