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Author Topic:   40k-Year-Old Man Had Recent Neanderthal Ancestor
Taq
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Posts: 7272
Joined: 03-06-2009
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Message 16 of 25 (761452)
07-01-2015 1:15 PM
Reply to: Message 6 by Jon
06-23-2015 7:25 PM


The issue of interbreeding was discussed in the other thread (linked to in the OP). But basically, the OOA tree model fails to account for the fact that while we carry recent African-origin genetic material we also carry genes of recent non-African origin, which is and always has been the MH position.

The two models have never been mutually exclusive. If about 5% of our genomes are from crossbreeding and the other 95% from our African ancestors, then the MH model explains 5% of our genome and the OOA model explains 95% of our genome.

It's a bit like the "argument" between gradualism and punctuated equilibria. You can have both.


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Jon
Inactive Member


Message 17 of 25 (761493)
07-01-2015 8:17 PM
Reply to: Message 15 by caffeine
07-01-2015 12:56 PM


Or they were just swamped by the expanding African genes...

That's a better way of saying what I was trying to say, though!

I'm glad you think so. Because the difference is the essence of the difference between MH and OOA.

MH explains the evolution/distribution of modern Homo sapiens as largely a product of gene movement.

OOA explains the evolution/distribution of modern Homo sapiens as largely a product of people movement.

Edited by Jon, : codes...


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Jon
Inactive Member


Message 18 of 25 (761494)
07-01-2015 8:24 PM
Reply to: Message 16 by Taq
07-01-2015 1:15 PM


The two models have never been mutually exclusive. If about 5% of our genomes are from crossbreeding and the other 95% from our African ancestors, then the MH model explains 5% of our genome and the OOA model explains 95% of our genome.

It's a bit like the "argument" between gradualism and punctuated equilibria. You can have both.

I think MH works fine with the observation that 95% of our genome is African while 5% is from sources outside of Africa.

Where the theories differ is in explaining why that distribution exists. MH explains it as a result of African genes swamping non-African ones (the genes were superior, more numerous, etc.) with little need for the large population movements posited by OOA.

MH works as an explanation for the genetic evidence, to be fair, OOA does too, but MH has the added benefit of explaining the physical evidence and matters such as regional continuity of completely random traits.


Love your enemies!

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caffeine
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Posts: 1358
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 3.5


Message 19 of 25 (761546)
07-02-2015 2:42 PM
Reply to: Message 17 by Jon
07-01-2015 8:17 PM


I'm glad you think so. Because the difference is the essence of the difference between MH and OOA.

MH explains the evolution/distribution of modern Homo sapiens as largely a product of gene movement.

OOA explains the evolution/distribution of modern Homo sapiens as largely a product of people movement.

The idea of genes moving without any significant movement of populations was sufficient to explain the fact the mtDNA had a recent African origin, but if we're talking more than 90% of the genome it doesn't seem reasonable to think this happened without lots of people carrying these genes. Individual genes could easily spread with no significant population movement by means of selection. But why should the selectively neutral bits of the genome from Africa come to dominate everywhere without being carried by an expanding African population?


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Jon
Inactive Member


Message 20 of 25 (761590)
07-02-2015 9:02 PM
Reply to: Message 19 by caffeine
07-02-2015 2:42 PM


The idea of genes moving without any significant movement of populations was sufficient to explain the fact the mtDNA had a recent African origin, but if we're talking more than 90% of the genome it doesn't seem reasonable to think this happened without lots of people carrying these genes.

More than 90% of which genome? The fella in question wasn't 90% African.

The 90% African distribution is the result of millennia of gene flow out of Africa.

But why should the selectively neutral bits of the genome from Africa come to dominate everywhere without being carried by an expanding African population?

Whether the dominance of African genes was brought about by migration or breeding, the evidence rather suggests that the African genes were anything but 'neutral'they're the genes that won.


Love your enemies!

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caffeine
Member
Posts: 1358
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 3.5


Message 21 of 25 (761757)
07-05-2015 5:31 AM
Reply to: Message 20 by Jon
07-02-2015 9:02 PM


More than 90% of which genome? The fella in question wasn't 90% African.

The 90% African distribution is the result of millennia of gene flow out of Africa.

So, you're proposing not one large population expansion in the last hundred thousand years, but a continually expanding African population? How is this simpler?

Whether the dominance of African genes was brought about by migration or breeding, the evidence rather suggests that the African genes were anything but 'neutral'they're the genes that won.

But unless you're suggesting that there is no such thing as a selectively neutral difference the dominance of African alleles cannot be due solely to selection.


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Jon
Inactive Member


Message 22 of 25 (761764)
07-05-2015 9:22 AM
Reply to: Message 21 by caffeine
07-05-2015 5:31 AM


So, you're proposing not one large population expansion in the last hundred thousand years, but a continually expanding African population?

No; I am 'proposing' (actually just repeating what countless scientists have proposed) a continual expansion of African genes.

How is this simpler?

It's not. It's messy and complicated like real life.

But unless you're suggesting that there is no such thing as a selectively neutral difference the dominance of African alleles cannot be due solely to selection.

The African genes were clearly superior; both theories recognize this fact.


Love your enemies!

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NoNukes
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Posts: 10115
From: Central NC USA
Joined: 08-13-2010
Member Rating: 1.7


Message 23 of 25 (761770)
07-05-2015 12:06 PM


Does anyone have any pointers to some reference material about these theories (other than the article in the OP)? I don't know anything about the topic, but I'd like to.l

Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)

History will have to record that the greatest tragedy of this period of social transition was not the strident clamor of the bad people, but the appalling silence of the good people. Martin Luther King

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caffeine
Member
Posts: 1358
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 3.5


Message 24 of 25 (761930)
07-06-2015 4:32 PM
Reply to: Message 22 by Jon
07-05-2015 9:22 AM


The African genes were clearly superior; both theories recognize this fact.

That's not true. Most proponents of multiregionalism that I've read ascribe the dominance of African ancestry to the size of the ancient African population. The issue is that it's not just our genes that are primarily of recent African origin - it's all the rest of the genome as well, and it's not reasonable that all of this was selectively advantageous - including every non-coding region and all the synonymous mutations.

You need significant expansion of people carrying genes to account for this. Genes need people to move them about, and while individual genes with a selective advantage can easily be passed around from population to population without much movement of people, only large migrations can explain whole genomes spreading themselves around.

Alan Templeton's model of human migrations out of Africa, which was based on mtDNA and Y-chromosone DNA, showed the genetic evidence was best explained by three migrations out of Africa - when Homo erectus first left about 1.8 million years ago, another at 700,000 years ago and the last recent one. Templeton is a multiregionalist, but like everyone else he accepts that we need population expansions from Africa to explain the genetic data. The only concrete dispute between multiregionalism and OOA is the question of how much gene flow was happening in between these major migrations and how big a contribution non-African populations made to the modern gene pool.


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caffeine
Member
Posts: 1358
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 3.5


Message 25 of 25 (761932)
07-06-2015 4:37 PM
Reply to: Message 23 by NoNukes
07-05-2015 12:06 PM


Does anyone have any pointers to some reference material about these theories (other than the article in the OP)? I don't know anything about the topic, but I'd like to.l

Most of what I read on the topic I discovered by following the blog of John Hawks, a palaeoanthropologist at the University of Wisconsin-Madison. If you look here there's a link to all the posts tagged 'introgression', which will be dealing with archaic populations genetic contribution to modern humans. You'll find there many links to open-access articles and other blogs on the topic as well as his own posts.

ABE: Population structure is another good tag for finding relevant posts.

Edited by caffeine, : No reason given.


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