Understanding through Discussion


Welcome! You are not logged in. [ Login ]
EvC Forum active members: 86 (8915 total)
Current session began: 
Page Loaded: 07-19-2019 12:18 PM
31 online now:
Chatting now:  Chat room empty
Newest Member: 4petdinos
Post Volume:
Total: 857,032 Year: 12,068/19,786 Month: 1,849/2,641 Week: 358/708 Day: 52/81 Hour: 1/12


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   40k-Year-Old Man Had Recent Neanderthal Ancestor
caffeine
Member
Posts: 1677
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 6.2


Message 10 of 25 (761174)
06-29-2015 11:25 AM
Reply to: Message 6 by Jon
06-23-2015 7:25 PM


According to the article, the individual in question is not an ancestor of any modern human populations.

Of course, there is no way that could be known.

Whether this sort of thing is considered as disproving an OOA model depends on exactly what you mean by 'out-of-Africa'. The idea of total replacement has been pretty convincingly disproven by the genetic evidence that we do carry genes from many archaic, non-African populations.

But whilst this extreme version of out of Africa is disproved by the genetic evidence, so is the extreme version of the multiregional hypothesis, since modern populations in Europe and Asia seem to have inherited only a minority of their genes from the middle Palaeolithic inhabitants of Europe and Asia. It looks like there was a population expansion from Africa, but that the expanding population interbred with local populations. The genetic signature of these archaic populations was mostly swamped by the expanding Africans - except for a few genes, most of which presumably were locally adaptive.


This message is a reply to:
 Message 6 by Jon, posted 06-23-2015 7:25 PM Jon has responded

Replies to this message:
 Message 11 by jar, posted 06-29-2015 11:31 AM caffeine has responded
 Message 13 by Jon, posted 06-29-2015 8:52 PM caffeine has responded

  
caffeine
Member
Posts: 1677
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 6.2


Message 12 of 25 (761198)
06-29-2015 1:55 PM
Reply to: Message 11 by jar
06-29-2015 11:31 AM


I don't think anyone has ever suggested that humans stopped screwing around just because they left Africa. I remember seeing a cave wall that said "What happened in Romania stays in Romania."

I don't think anyone has thought that emerging humans didn't screw anyone they found along their road trips.

Several people have argued that there was no interbreeding between the recent emigrants from Africa and archaic humans elsewhere, and this is not just an old-fashioned view - some still argue in favour of the idea today. Here's an article from the American Journal of Physical Anthropology from as recent as 2011 arguing that the apparent sign of Neanderthal DNA in non-African populations is better explained by ancient African population structure than interbreeding.

ABE: On further thought, I'm willing to concede you're probably right about this. I was trying to find a clear statement from supporters of the total replacement model, but the most confident claims that there was no admixture go more like this:

quote:
We indeed show that the absence of Neanderthal mtDNA sequences in Europe is compatible with at most 120 admixture events between the two populations despite a likely cohabitation time of more than 12,000 y. This extremely low number strongly suggests an almost complete sterility between Neanderthal females and modern human males, implying that the two populations were probably distinct biological species.

So I guess it's not really a claim that modern humans didn't get it on with archaic humans, but simply that they couldn't make babies (or not fertile ones at least)

Edited by caffeine, : No reason given.


This message is a reply to:
 Message 11 by jar, posted 06-29-2015 11:31 AM jar has not yet responded

Replies to this message:
 Message 14 by RAZD, posted 06-30-2015 7:12 AM caffeine has not yet responded

  
caffeine
Member
Posts: 1677
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 6.2


Message 15 of 25 (761445)
07-01-2015 12:56 PM
Reply to: Message 13 by Jon
06-29-2015 8:52 PM


I think you mean that modern populations in Europe and Asia seem to have preserved only a minority of their Neanderthal genes.

Isn't that a different way of saying the same thing?

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

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


This message is a reply to:
 Message 13 by Jon, posted 06-29-2015 8:52 PM Jon has responded

Replies to this message:
 Message 17 by Jon, posted 07-01-2015 8:17 PM caffeine has responded

  
caffeine
Member
Posts: 1677
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 6.2


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?


This message is a reply to:
 Message 17 by Jon, posted 07-01-2015 8:17 PM Jon has responded

Replies to this message:
 Message 20 by Jon, posted 07-02-2015 9:02 PM caffeine has responded

  
caffeine
Member
Posts: 1677
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 6.2


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.


This message is a reply to:
 Message 20 by Jon, posted 07-02-2015 9:02 PM Jon has responded

Replies to this message:
 Message 22 by Jon, posted 07-05-2015 9:22 AM caffeine has responded

  
caffeine
Member
Posts: 1677
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 6.2


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.


This message is a reply to:
 Message 22 by Jon, posted 07-05-2015 9:22 AM Jon has not yet responded

  
caffeine
Member
Posts: 1677
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 6.2


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.


This message is a reply to:
 Message 23 by NoNukes, posted 07-05-2015 12:06 PM NoNukes has not yet responded

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2018 by EvC Forum, All Rights Reserved

™ Version 4.0 Beta
Innovative software from Qwixotic © 2019