There are two primary hypotheses for how modern human beings evolved worldwide. One is the "recent African replacement" hypothesis: modern humans only left Africa some time in the last 100,000 years or so, and replaced all other hominins on the planet. The other is the "multiregional" hypothesis: that after the spread of homo erectus from Africa throughout the old world about 2,000,000 years ago, evolution was multiregional, with modern humans being a mix of these ancient human lineages.

This thread is for evidence and discussion relevant to these competing hypotheses. I'll start with a link to a lecture that summarizes a lot of the relevant information:

http://www.youtube.com/watch?v=Ff0jwWaPlnU

The most relevant part is between 35 and 50 minutes in, first discussing evidence that supports the recent African replacement hypothesis, then discussing some evidence that seems to indicate a contribution to the modern East Asian human genome from ancient Asian homo erectus lineages, which would tend to support the multiregional hypothesis.

http://johnhawks.net/weblog/topics/modern_human_origins/multiregional_vs_out_of_africa.html

Here's a quick summary of the differences.

The problem

To begin with, both hypotheses try to account for the evolution of today's humans from our Pleistocene ancestors. The difference between the hypotheses is in which Pleistocene people were our ancestors, and which were not.

Both hypotheses have to account for the same basic set of facts:

* Humans first left Africa and established populations in other parts of the world (first southern Asia, China, and Java, later Europe) by 1.8 million years ago.
* Humans today are quite different anatomically and behaviorally from archaic people (that is, most humans before 40,000 years ago) anywhere in the world. Recent people are called "modern" humans.
* Human populations today are genetically very similar to each other.
* African populations today are more genetically diverse than populations in other parts of the world.
* Recent humans in Europe and Asia share a few features with the ancient archaic people who lived in those places before 40,000 years ago.

Out of Africa

Under the Out of Africa hypothesis, the first humans to leave Africa 1.8 million years ago divided into several different species during the Pleistocene. Species, of course, are defined by reproductive isolation, so the evolution of these several species of humans was separate. The fossil archaic humans that we find throughout the Old World belonged to these several species, but only one branch of this ancient family tree could give rise to today's humanity.

This branch was African. The origin of modern humans in Africa explains why today's Africans are more genetically variable than other populations --- they were the first human population to expand, and other populations (like those of Europe and Asia) were founded later. The recent origin explains why today's human populations are genetically similar -- they haven't had time to diverge very much.

The resemblances with archaic humans in some modern people are explained either as a result of parallel evolution --- the same selection in the same place leads to similar features --- or as a result of slight genetic contributions from archaic humans into today's populations.

Multiregional evolution

Under the Multiregional evolution hypothesis, the first humans to leave Africa 1.8 million years ago never divided into different species. Instead, these populations always exchanged genes with each other through recurrent gene flow. Today, we are part of this same species, which has evolved greatly over time to a very different morphology and behavior from the first humans.

The low genetic differences among human populations are a result of a history of gene flow between ancient populations. Our present morphology and behavior have greatly changed from archaic humans because of natural selection in a global human population. Resemblances between archaic and modern humans in some parts of the world are the result of ancestry.

The greater genetic variation within Africa is a consequence of larger African population size, greater ecological diversity and local selection, or both. These factors gave Africa a dominant role in the ancestry of today's human population.

Tyrannical wrote:http://johnhawks.net/weblog/topics/modern_human_origins

The resemblances with archaic humans in some modern people are explained either as a result of parallel evolution --- the same selection in the same place leads to similar features --- or as a result of slight genetic contributions from archaic humans into today's populations.

I don't think that's a reasonable definition. Any local genetic contribution is multiregional. A slight local contribution is still a multiregional contribution, albeit a slight one.

Warren Dew wrote:

Tyrannical wrote:http://johnhawks.net/weblog/topics/modern_human_origins

The resemblances with archaic humans in some modern people are explained either as a result of parallel evolution --- the same selection in the same place leads to similar features --- or as a result of slight genetic contributions from archaic humans into today's populations.

I don't think that's a reasonable definition. Any local genetic contribution is multiregional. A slight local contribution is still a multiregional contribution, albeit a slight one.

Yes, well I assume the Out of Africa theory had to add that little bit as I believe the evidence now shows some Neanderthal admixture in Europeans.

John Hawks' doctoral advisor was Milford Wolpoff, who is well known as an innovator of the "multiregional" theory of modern human origins. The text I copied from Hawks was from a study guide for his students I found on his blog.

Please explain to me how does this account for the fact that every single human can be traced back to a common ancestor, not a common pair of ancestors but one common ancestor, it's because even if people moved around in different ways, they still can trace their ancestry back to that common ancestor.

Indians the ancestors of Asians.
Watch Dawkins on the video.

I see the word "species" above. Humans are not different species. They might develop a different look according to their climate but they are the same species. If they weren't they wouldn't be able to interbreed.

A hybrid between two species cannot reproduce: mules, a cross between a horse and a donkey, are sterile; ligers, a cross between a male lion and a female tiger, the males are sterile, they never go through puberty and are therefore not as aggressive as their lion fathers, the females are fertile, but they have to mate with lions, because a tigron, i.e. a cross between a male tiger and a female lion, has never been bred successfully.

So the whole idea of people of different races being a different "species" falls down on that point alone. If 'black' people were a different 'species' they would not have fertile offspring with 'white' people, and we all know that isn't true, Barack Obama is proof of that isn't he?

Agrippina wrote:

I see the word "species" above. Humans are not different species. They might develop a different look according to their climate but they are the same species. If they weren't they wouldn't be able to interbreed.

While that is a common misconception, it is not the definition of species.

http://evolution.berkeley.edu/evosite/evo101/VA1BioSpeciesConcept.shtml
For example......

Ring species are species with a geographic distribution that forms a ring and overlaps at the ends. The many subspecies of Ensatina salamanders in California exhibit subtle morphological and genetic differences all along their range. They all interbreed with their immediate neighbors with one exception: where the extreme ends of the range overlap in Southern California, E. klauberi and E. eschscholtzii do not interbreed. So where do we mark the point of speciation?

How ever, in the Out Of Africa theory, they were different species and could not (or did not) interbreed. Though I believe they admit there could have been some small amount of admixture.

Tyrannical wrote:

Agrippina wrote:

I see the word "species" above. Humans are not different species. They might develop a different look according to their climate but they are the same species. If they weren't they wouldn't be able to interbreed.

While that is a common misconception, it is not the definition of species.

http://evolution.berkeley.edu/evosite/evo101/VA1BioSpeciesConcept.shtml
For example......

Ring species are species with a geographic distribution that forms a ring and overlaps at the ends. The many subspecies of Ensatina salamanders in California exhibit subtle morphological and genetic differences all along their range. They all interbreed with their immediate neighbors with one exception: where the extreme ends of the range overlap in Southern California, E. klauberi and E. eschscholtzii do not interbreed. So where do we mark the point of speciation?

How ever, in the Out Of Africa theory, they were different species and could not (or did not) interbreed. Though I believe they admit there could have been some small amount of admixture.

Contribution of non-Homo sapiens species nuclear DNA to Homo sapiens hasn't been shown though. The much awaited Neanderthal genome still hasn't been published IIRC.

I was under the impression that the latest conclusion was that there was no Neanderthal contribution to the H sapiens genome. However, that impression is based on popular articles read on the net.

Tyrannical wrote:

Agrippina wrote:

I see the word "species" above. Humans are not different species. They might develop a different look according to their climate but they are the same species. If they weren't they wouldn't be able to interbreed.

While that is a common misconception, it is not the definition of species.

Sorry but I quote:

Out of Africa

Under the Out of Africa hypothesis, the first humans to leave Africa 1.8 million years ago divided into several different species during the Pleistocene.

(My bold)

I keep asking for a scientist on the forum to come forward to resolve this issue. Everything I've read says that we are all descended from the same original ancestor whose descendents left Africa. I keep posting the links to the National Geogrpahic pages and everybody just ignores them. Watch the video here: The Human Family Tree. It is interesting, go through the intro and then go to the interactive map on the next page.

Are you saying that National Geographic are lying when they say that Homo Erectus came out of Africa to populate the entire world and that we didn't mix our genes with the previous humans? Please don't believe me. Ask the scientists.

Agrippina wrote:

I keep asking for a scientist on the forum to come forward to resolve this issue. Everything I've read says that we are all descended from the same original ancestor whose descendents left Africa. I keep posting the links to the National Geogrpahic pages and everybody just ignores them. Watch the video here: The Human Family Tree. It is interesting, go through the intro and then go to the interactive map on the next page.

That's because all you are reading is the Out of Africa Theory. Prof. John Hawks, is a scientist, and is a proponent of the Multiregional Theory which is different.

Are you saying that National Geographic are lying when they say that Homo Erectus came out of Africa to populate the entire world and that we didn't mix our genes with the previous humans? Please don't believe me. Ask the scientists.

No, I am saying that National Geographic is presenting the Out of Africa Theory, which may be wrong. Hence the competing theories.

Tyrannical wrote:

Agrippina wrote:

I keep asking for a scientist on the forum to come forward to resolve this issue. Everything I've read says that we are all descended from the same original ancestor whose descendents left Africa. I keep posting the links to the National Geogrpahic pages and everybody just ignores them. Watch the video here: The Human Family Tree. It is interesting, go through the intro and then go to the interactive map on the next page.

That's because all you are reading is the Out of Africa Theory. Prof. John Hawks, is a scientist, and is a proponent of the Multiregional Theory which is different.

Are you saying that National Geographic are lying when they say that we came out of Africa to populate the entire world and that we didn't mix our genes with the previous humans? Please don't believe me. Ask the scientists.

No, I am saying that National Geographic is presenting the Out of Africa Theory, which may be wrong. Hence the competing theories.

Well isn't it odd that NatGeo are not finding any Neanderthals out there.
And seriously? Seriously? Do you want to know that your ancestors might have been neanderthals?

Did you even look at the map? Of course not, to do that might interfere with the meme that says: Africans are something we are entitled to ............. whatever! We are all descended from Africans no matter what the new earthers are saying the people they are talking about are the people who settled in India and from whom all Asians are descended.

There has been a cult of new-earthers in China who held for a long time that the Chinese were descended from Cro Magnon man and that was until NatGeo proved they were wrong. There was a 'black' man in New York who believed he was African until they proved that he was more Middle Eastern than he was African, and a person who thought they were pure white American mixed with a Latino, and it turned out that they were descended from Malaysians.

Because the bible justification has been shown to be incorrect, just like with ID, new earthers are intent to proving that their 'blood' is whiter than those other people and so far, they have not been proved to be correct with DNA. If you don't believe me, get your DNA tested by NatGeo and see what it says.

We shared space with Neanderthals at some stage and they also shared space with Cro Magnon but in the end it was Homo Sapiens that survived.

Here's a good read: Did all humans descend from the same ancestor?
Here's another.

Tyrannical wrote:
That's because all you are reading is the Out of Africa Theory. Prof. John Hawks, is a scientist, and is a proponent of the Multiregional Theory which is different.

It still an argument from authority to rely solely on the works of Prof. Hawks, who himself may be biased as an ex-student of Prof. Milpoff. Rather one should critically appraise the data to hand before drawing conclusions. Now from the literature I've read both hypotheses have merit, however, OOA appears to explain more of the evidence than MR does as it stands. Should new evidence come to light that this is not the case then I will revise my conclusions. However, based upon the evidence OOA seems the most likely candidate (perhaps with some revision as befits a good scientific hypothesis).

I'm not disparaging Prof. Hawkes as a reliable source on human evolution, I'm just saying its a tad naive to get ones information from a single, potentially biased, source.

MedGen wrote:

Tyrannical wrote:
That's because all you are reading is the Out of Africa Theory. Prof. John Hawks, is a scientist, and is a proponent of the Multiregional Theory which is different.

It still an argument from authority to rely solely on the works of Prof. Hawks, who himself may be biased as an ex-student of Prof. Milpoff. Rather one should critically appraise the data to hand before drawing conclusions. Now from the literature I've read both hypotheses have merit, however, OOA appears to explain more of the evidence than MR does as it stands. Should new evidence come to light that this is not the case then I will revise my conclusions. However, based upon the evidence OOA seems the most likely candidate (perhaps with some revision as befits a good scientific hypothesis).

I'm not disparaging Prof. Hawkes as a reliable source on human evolution, I'm just saying its a tad naive to get ones information from a single, potentially biased, source.

what he said!

MedGen wrote:

Tyrannical wrote:
That's because all you are reading is the Out of Africa Theory. Prof. John Hawks, is a scientist, and is a proponent of the Multiregional Theory which is different.

It still an argument from authority to rely solely on the works of Prof. Hawks, who himself may be biased as an ex-student of Prof. Milpoff. Rather one should critically appraise the data to hand before drawing conclusions. Now from the literature I've read both hypotheses have merit, however, OOA appears to explain more of the evidence than MR does as it stands. Should new evidence come to light that this is not the case then I will revise my conclusions. However, based upon the evidence OOA seems the most likely candidate (perhaps with some revision as befits a good scientific hypothesis).

I'm not disparaging Prof. Hawkes as a reliable source on human evolution, I'm just saying its a tad naive to get ones information from a single, potentially biased, source.

Yes, if I may remind you I have not stated any opinion on the matter as of yet. All I posted was a summary of what each of the two theories were, and what questions the theories have to answer. Do you see something controversial with how he defines the two theories?

Tyrannical wrote:Yes, well I assume the Out of Africa theory had to add that little bit as I believe the evidence now shows some Neanderthal admixture in Europeans.

Well, first off, if the evidence showed that, the honest thing to do would be to admit that it showed that the multiregional theory is at least partly correct, rather than try to redefine the "recent out of Africa" theory to mean something other than out of Africa.

Secondly, do you know what your source is for this? The reason I ask is that, while I thought the same thing as you at one point, some of the papers that I based this opinion on were subsequently refuted. The information I'm aware of may be worth going over in a little more detail.

A few years ago samples of a 38,000 year old neanderthal fossil were analyzed for DNA comparison with modern humans by two groups.

The European group, headed by RE Green at the Max Planck institute, concluded that the neanderthals were nearly as closely related to modern humans as modern humans are to each other; they estimated a mean DNA divergence time between humans and neanderthals of 516,000 years ago, and between two humans of 459,000 years ago. The implication was that the divergence between neanderthal and modern human populations only happened very recently, or perhaps never happened at all, with neanderthal morphological traits simply being subsumed into the modern human population.

The American group, headed by JP Noonan, analyzing samples from the same neanderthal using different techniques, came up with rather different conclusions. They estimated a DNA divergence time of 706,000 years ago, and a population split of 370,000 years ago, "before the emergence of anatomically modern humans."

In light of these apparently contradictory results, Wall & Kim of the University of California reanalyzed both sets of data using a single analysis method for both. They confirmed the disparate results between the two sets of data, specifically including major incompatibilities with respect to population split times and neanderthal contribution to the modern European genome.

They then performed some additional analyses of the Green data, analyzing differences in human neanderthal correlation between sequences of different lengths, and concluded that of various possible scenarios for accounting for the Green data, the most likely scenario was that the Green data resulted from sample contamination by human DNA.

This was further complicated by the fact that in the initial version of Wall & Kim's paper, they arbitrarily rejected the possible explanation that humans and neanderthals were always a single population, an explanation which fit their initial analysis even better than sample contamination. That weakness originally caused me to view their paper as suspect. However, since that time, they have published a revised version of their paper with further analysis that that tends to disprove the single population hypothesis. The Green group has largely accepted the conclusions of Wall & Kim, admitting to sample contamination.

So, as things stand now, the most reliable conclusion is probably that of Wall & Kim based on the Noonan data. That conclusion places the population split time between neanderthals and modern human at about 400,000 years ago, with subsequent neanderthal contribution to the modern human genome of no more than 20% (95% confidence interval), with a best estimate of 0%. The full text of the Wall & Kim paper is available at:

http://www.ncbi.nlm.nih.gov/pmc/article ... =pmcentrez

Abstracts of the Noonan and Green articles can be found at:
http://www.ncbi.nlm.nih.gov/pubmed/17110569
http://www.ncbi.nlm.nih.gov/pubmed/17108958

Obviously that's based on only one neanderthal individual, so things could change, but at present there's no evidence of any neanderthal contribution to the modern human genome, and at least some evidence against it.

If you have more recent sources based on other data, though, I'd be very interested.

Spearthrower has a thread listing some Anthropology resources, worth checking out.
http://www.rational-skepticism.org/anthropology/anth-resources-thread-plan-t1650.html

Warren Dew wrote:

Tyrannical wrote:Yes, well I assume the Out of Africa theory had to add that little bit as I believe the evidence now shows some Neanderthal admixture in Europeans.

Well, first off, if the evidence showed that, the honest thing to do would be to admit that it showed that the multiregional theory is at least partly correct, rather than try to redefine the "out of Africa" theory to mean something other than out of Africa.

Secondly, do you know what your source is for this? The reason I ask is that, while I thought the same thing as you at one point, some of the papers that I based this opinion on were subsequently refuted. The data I'm aware of may be worth going over in a little more detail.

I was probably just being smug about it.
I don't know exactly what the original Out of Africa hypothesis claimed. And it is unfair to hold something to it's original unrevised version. There were some morphological similarities between archaic humans and the modern day human populations, and I don't think that was a new finding. For example, shoveled teeth in Asians.

A few years ago samples of a 38,000 year old neanderthal fossil were analyzed for DNA comparison with modern humans by two groups.

The European group, headed by RE Green at the Max Planck institute, concluded that the neanderthals were nearly as closely related to modern humans as modern humans are to each other; they estimated a mean DNA divergence time between humans and neanderthals of 516,000 years ago, and between two humans of 459,000 years ago. The implication was that the divergence between neanderthal and modern human populations only happened very recently, or perhaps never happened at all, with neanderthal morphological traits simply being subsumed into the modern human population.

Not Humans, only European Caucasian Humans, which are more closely related to Neanderthal than to sub-Saharan Africans. Or at least that is what I have read.

The American group, headed by JP Noonan, analyzing samples from the same neanderthal using different techniques, came up with rather different conclusions. They estimated a DNA divergence time of 706,000 years ago, and a population split of 370,000 years ago, "before the emergence of anatomically modern humans."



This was further complicated by the fact that in the initial version of Wall & Kim's paper, they arbitrarily rejected the possible explanation that humans and neanderthals were always a single population, an explanation which fit their initial analysis even better than sample contamination. That weakness originally caused me to view their paper as suspect. However, since that time, they have published a revised version of their paper with further analysis that that tends to disprove the single population hypothesis. The Green group has largely accepted the conclusions of Wall & Kim, admitting to sample contamination.

So, as things stand now, the most reliable conclusion is probably that of Wall & Kim based on the Noonan data. That conclusion places the population split time between neanderthals and modern human at about 400,000 years ago, with subsequent neanderthal contribution to the modern human genome of no more than 20% (95% confidence interval), with a best estimate of 0%. The full text of the Wall & Kim paper is available at:

Yup, I do remember that release. I don't think they've released the final report with a 100% of the genome done. Of course that "new lineage" they just discovered makes you wonder what else there may be. It only takes one fossil to turn everything upside down

Those date estimates are based on a molecular clock and mutation rates and population size, and other mumbo jumbo I don't fully understand. But they aren't written in stone, and some recent research has hinted that some of our assumptions about it may be flawed. Regardless, it needs to be looked at more closely.

Tyrannical wrote:Spearthrower has a thread listing some Anthropology resources, worth checking out.

http://www.rational-skepticism.org/anthropology/anth-resources-thread-plan-t1650.html

For active links, use the URL button rather than Quote. The result should look like this: http://www.rational-skepticism.org/anthropology/anth-resources-thread-plan-t1650.html, or like this.

MedGen wrote:Contribution of non-Homo sapiens species nuclear DNA to Homo sapiens hasn't been shown though. The much awaited Neanderthal genome still hasn't been published IIRC.

I agree that no neanderthal contribution to the homo sapiens genome has been shown, based on the Wall & Kim paper I just posted about. I think the current neanderthal genome project is unlikely to change this, since the neanderthal being analyzed is apparently far from the neanderthal/human range interface, and thus isn't likely to have been closely related to any admixture.

However, I think there is strong evidence for a different contribution from outside homo sapiens, specifically from Asian homo erectus. See for example the 2005 paper "Evidence for Archaic Asian Ancestry on the Human X Chromosome" from Molecular Biology and Evolution:

Garrigan et. al. wrote:A gene tree constructed from a 2.4-kb fragment of the RRM2P4 locus sequenced in a sample of 41 worldwide humans clearly roots in East Asia and has a most-recent common ancestor approximately 2 Myr before present. The presence of this basal lineage exclusively in Asia results in higher nucleotide diversity among non-Africans than among Africans [for this gene].... We suggest that this ancient lineage is a remnant of introgressive hybridization between expanding anatomically modern humans emerging from Africa and archaic populations in Eurasia.

http://mbe.oxfordjournals.org/cgi/content/full/22/2/189

This and other similar results are discussed between 44 and 49 minutes into the lecture I posted in the original post of this thread, with the key points starting about 46 minutes in. Basically these loci are evidence for ancient homo erectus contribution to the modern human genome, at least in modern Asians.