Evolutionists..Out of it in Africa?

Why does popular science media(and the general media) buy this model for recent human evolution so readily? A mitochodrial eve’s family sprung up in Africa 100,000 years ago, developed slightly better rocks than the rest of the world, and stormed out of Africa completely decimating well established populations with the same cranial capacity(I’m thinking specifically of Neanderthals) with no interbreeding. The TLC “Walking with Cavemen” was the inspiration for this thread, though it seems most other science media purports this as the only scenario, with maybe a small mention in passing of others (specifically multiregionalism). The debate in the bio-anthro society is far from resolved. In short, multiregionalism postulates that humans have been human for much longer, closer to 1 mya, when specimens of H. erectus(Turkana) can be found with roughly modern post-cranial human anatomy(a bit more rugose) and more rugose cranial anatomy. Human populations never migrate in only one direction, rarely contact each other without interbreeding. I think morphological differences between the so-called “modern” populations and “archaics” could be easilly accounted for by regional(racial, for lack of a better term) differences, much as there are regional differences between human populations now. We’re talking about small measurements between different points on the cranium. Morphology does not a speciation make, by way of example, I submit to you the Great Dane and the chihuahua. Tool use? If it ain’t broke don’t fix it. Remember, when Europeans first encountered some populations in Tasmania and elsewhere, they were still using stone, bone and sticks not far removed from the axe-blades and choppers so commonly used as evidence that
somehow Neanderthals are a separate species. Other evidence is largely baseless, Neanderthals didn’t have the capacity for speach, abstract thought or plannig for the future. Bah. There is no reason for a 1500-1800 cc brain unless you are going to use it, as can cost 20% of your daily energy intake. the genetic clock which places “Eve” in Africa 100,000 years ago is not perfect, and was developed by geneticists, not paleoanthropologists. There are fossils that show regional continuity, going back over a much longer period than the Out of Africa model posits we have been “fully” human. For example, Zhoukodian in China, where cranial material with shoveled incissors( a trait found in modern east Asian poulations today) is fro at least 150,000 years ago. There are other examples of regional continutiy as well, but this OP is getting long, so to the point, convince me that modern humans arose in Africa 100,000 years ago, stormed from the continent and completely replaced their cousins on the entire rest of the planet in this short span of time, and do a better job tahn Alec Baldwin or I shall remain unconvinced.

…I have been reading the Internet Infidels board to much, where people use the term evilutionist as a point of pride. EVOLUTIONISTS…

Agh, my eyes. Too primative I guess, prefer paragraphs. :wink:

While it may bepossible that the popular media is currently pronouncing Out Of Africa a bit onesidedly, I think that this is a function of the standard approach to simplification that the popular media always uses in the interest of presenting an easy-to-follow thesis.

However, I suspect that the media has it right, this time. The strongest evidence for Out Of Africa and against Multi-Regionalism has been genetic–not just mtDNA, but the entire suite of alleles, with the greatest diversity in Africa and progressively less diversity (with significant examples of founder effect) occurring in each region more distant from Africa. There is certainly evidence of “backflow” into Africa, but it is consistent with the Out Of Africa theory and does little to support Multi-Regionalism.

Based on cultures or physical resemblance, we could posit a number of scenarios, but the genetic evidence is rather strongly supportive only of OOA.

I agree with Tom, the media tends to oversimplify things (it’'s all about the lowest-common-denominator). But as far as “walking with Cavedonkeys” is concerned (I haven’t seen it), it may depend more upon who’s paying the bill than interest in alternative evidence.

Yes, the popular media prefers a simple approach. But, as Tom said, the genetic evidence for OoA is pretty strong. Probably the biggest nail in the coffin is the DNA evidence comparison between Sapiens and Neanderthals indicating that the two groups shared a common ancestor no more recent than 500k yrs ago. More data is needed (I think only 4 Neanderthal samples have been studies so far), but the evidence does point toward OoA.

On the other hand, if you picked up the recent special publication by Scientific American on human evolution, there is an entire article devoted to the Multiregional theory. It is presented as a viable alternative.

I have to say that I find it hard to believe the Sapiens and Neanderthal couldn’t interbreed successfully. And it does appear that Neanderthals adopted some of the “advanced” cultural practices of Sapiens once they appeared in Europe. But the data just doesn’t hold up to the idea that Neanderthals contributed appreciablly to our genetic makeup.

I wasn’t saying that Out of Africa is completely w/o merit. I personally don’t see the thoeries as competing. The DNA evidence is from a scant sampling, mostly British europeans, compared to very fragmented and degrded bits of Nenderthal DNA. Populations ebb and flow, and Out of Africa dosen’t handle the rest of the world very well. What may have happened in one region may be totally different from what occured in another. Tom, an alternative reson for the greatest genetic diversity in Africa is that as the cradle of humanity and best natural habitat, it has probably had the highest population density for the longest period of time.

ugh, forget the point, still addressing Tom’s post, this does nothing to support the timeframe given by Out of Africa’s mitochondrial Eve.

The DNA evidence that I am referring to is the DNA of current populations. It is extensive, and has been plotted across most of the globe. There is a very specific direction of DNA changes, with clear bottlenecks and founder effects throughout the human population. The lack of multiple radiant loci argues pretty strongly against Multi-Regional, simultaneous development. (If Africa is the “cradle” of humanity, does not that make the issue one of “Out of Africa” by default?)

I also question the notion that Africa had high population density for any significant period of history. Even when cultural/technological developments (such as agriculture) rolled back into Africa, it did not develop high population densities in places like the Sahel*, so at what point was Africa ever densely populated during the hunter-gatherer phase?

  • (There was higher density along the Nile, of course, but the Nile valley was in contact with the Fertile Crescent cultures for most of its higher density existence.)

Densely populated in comparison to Europe and Asia, the human population did not see anything like the upswing its taken toady untill after the period I’m refering to, during which most of our evolution occured.

QUOTE]*Originally posted by tomndebb *
**The DNA evidence that I am referring to is the DNA of current populations. It is extensive, and has been plotted across most of the globe. There is a very specific direction of DNA changes, with clear bottlenecks and founder effects throughout the human population. The lack of multiple radiant loci argues pretty strongly against Multi-Regional, simultaneous development. (If Africa is the “cradle” of humanity, does not that make the issue one of “Out of Africa” by default?)

No argument Sapiens came from Africa, I think where I generally disagree is with the total replacement of earlier populations. Also, given gene flow, its not “simultaneous development.” Humans operate a little differently as a species which has occupied far reaching corners of the globe yet at the same time stayed connected through gene flow(if there’s one thing that’s certain is that when human groups meet they interbreed) and constant migrations in and out of areas. Out of Africa makes it seem there is some morphological and cultural finish line to cross in order to be modern, my point is all one needs in order to be “modern” is to exist in the present. It’s odd how we don’t get quite so nitpicky about , oh say, horse evolution. No one tries to take mesohippus off the family tree.
I dont see how the direction of founder effect supports Eve either, why regional continuity in something like incissor shoveling in Asia, why would this trait evolve twice in the same region? I just think there are problems with the mitochondrial clock, it dosent always agree with paleontology and has been investigated for a much shorter time period. Of course we all came from Africa, just not all at once in a massive wave of modernity while our brethren were killed off or sputtered into extinction.

Why is that? I heard of their arguments but do not quite understand what they are getting at.

Moderator’s Note: Since it appears that labmonkey does not actually regard evolution as a Secular Humanist Plot to Corrupt Our Precious Bodily Fluids, I have edited the thread title slightly (a least as it appears on the main GD page) to correct his slip of the keyboard.

What they’re getting at is that one would expect the largest genetic variation to exist in the human population which has been in it’s ancestral area the longest. Humans who migrated out of Africa represent a subset of Africans, and so have less genetic diversity.

As for the shovel teeth issue in Asian Erectus, that finding is somewhat subjective and not generaly agreed upon by most anthropoligists. Perhaps if the fossil record in Asia in the 200k - 100k yrs ago was not so sparse, we’d have a better idea of what was going on in that region.

As an example, consider this situation: in the far northeastern region of (what is now) Siberia or in the far west of (what is now) Alaska, at about the time that one of the significant migrations from Asia to the Americas began, there was a single mutation in some guy’s Y chromosome to use thymine instead of cytosine in one of the DNA strings. Today, we can find Y chromosomes throughout the (male) inhabitants of the Americas who have the thymine string instead of the cytosine string. No one living in Africa, Europe, Oceania, or Asia (outside the farthest reaches of eastern Siberia)* has that trait. This is a bottleneck and a founder effect. The bottleneck is the geographic “funnel” of the proximity of Asia and America at that point. The founder effect is the passing of that single mutation into the population of the peoples who explored the Americas from a single individual, or founder. It is a one-way street. Since the cytosine/thymine switch occurs throughout all the Americas and exists in only a tiny number of individuals on the east of the Bering Sea, it presents geneticists with a good example of a change that followed a migration pattern.

Similar genetic traits have been found throughout humanity. When we examine the genetics of people across the world, we find that Africa has far more diversity than other continents. This implies that migrations leaving Africa have been subject to the founder effect, in that not every group who migrated out of Africa had all the diversity of the entire African continent, so the founder effect is demonstrted in each group that took only part of the African diversity with it. Similarly, once any group left Africa, it was always possible that it would diversify on its own through mutations (as with the Y-chromosome cytosine/thymine switch), however, each of those changes tend to follow the example of that switch and are now found fanning out along paths where migrations took place in the directions that the migrations took. They also tend to follow patterns away from Africa. There is a certain amount of “backwash” with groups reversing the migration patterns from time to time, but the overall trend is steadily away from Africa.

Thus my comment about radiant loci. We do not have examples of diversity occurring such that the patterns of DNA migration look as though they originated in multiple places and simply swirled around until they were all mixed together. The Y-chromosome change extends into the Americas without wandering back toward India or Europe. No other similar mutation has radiated outward from the Gobi Desert or France or wherever. The trends all show a general movement away from Africa.

labmonkey’s point, that I missed in the OP and our first exchange was that he was not arguing against an initial African origin of Homo (whether it be sapiens, erectus, habilis or whatever). Rather, he was challenging the simplified presentation that Homo sapiens made the same world-encompassing expansion that H. erectus (and possibly others) had made before, eradicating any predecessor groups as we swept over the world. He offers the possibility that once the initial expansion of any Homo group had colonized the world, the later expansion of H. sapiens might have interbred with its predecessors rather than killing them off.

The specifics of his point are directed toward Homo neanderthalis. For many years there have been discussions (debates/feuds/murderous attacks) regarding the issue of whether Neandertal were ancestral to modern humans (everyone now pretty much agrees that they were not direct lineal ancestors). The two strongest theories have been

  • that sapiens and neanderthalis interbred (as suggested by the Jane Auel novels with her periodic breeding of children with “mixed spirits,” usually as the result of rape) with our population eventually overwhelming their genes
  • that sapiens simply outcompeted neanderthalis (possibly accompanied by a bit of genocide) and that there was no interbreeding.

The theory that is currently most widely held is the second. A number of Neandertal remains were examined for DNA and it was determined that the Neandertal DNA was sufficiently different to rule out the possibility that we ever interbred with them.

While that is the current majority view, labmonkey’s position is that the basis of the comparison was flawed (insufficient sample size among other reasons) and that we should not be so quick to dismiss a possible linked sexual/genetic history between (at least) sapiens and neanderthalis. (I am not yet clear whether he is also arguing for a similar connection between sapiens and erectus.)

I am more familiar with the “mutiple regional” theory positing that H. sapiens arose from H. erectus in multiple locations and my responses were based on that misunderstanding of labmonkey’s position.

  • (Events since 1492 have pretty much guaranteed that we are liable to find any gene anywhere, but the principle is based on the general populations.)

tom, I was taught an updated and modified version of the multiregional model, as developed at by Dr. Milford Wolpoff at Uof M(Mich). This is not the same as the older model, put forth primarily by Carlton Coon, a very racially motivated man of his times. I’ve not actually worked or studied in the field(unfortunately cash calls) for awhile, when I did, there existed two very polarized camps. Anyway, Wolpoff decided not to “throw the baby out with the bathwater”, in regard to Coon’s basic theory, specifically that we have existed as humans for a very long time in different environs, possibly as far back as 1 mya, with populations separated, but constantly passing genes back and forth, never having a chance to speciate, but with enough distance to develop the racial traits we see today, through founder effect and environmental pressures. So you have centers where gene frequencies are high and clines in between as one group blends gradually into another. Thus, no real separate “races” just gradual east-west, north- south clines in gene frequency. I thought a elegant metaphor Dr. Wolpoff used(I will now shamelessly steal it) was tossing a few stones in a pond at once, there are epicenters, but the ripples overlap and move into one another in all directions.

ugh, forgot to mention, this in effect creates the situation where groups never actually have to make contact with one another…not large sweeping movements, rather, this village’s young men marry women from the next village(and vice versa) to the next, to the next, and on and on…with no one the wiser about what lies beyond their territory, but the group at the edge does knows whats over the hill. This was true up untill very recently, even hunter getherer groups do not range the distances required for a quick and dirty extermination of their neighbors to any significant degree. Right up untill historical times most people lived and died within miles of where they were born. The gray wolf is a good example of a pan-geographic animal which has kept itself together as a single species, with only minor phenotypic differences(like humans) arising.

Actually, when I think of the Multi-Regional Hypothesis, I generally think first of Wolpoff, who has raised a number of pertinent issues regarding physiognomic developments. I do not think that he had a “bad” hypothesis; it simply appears to me that the genetic record argues against him. As long as the only guideline we had was the fossil record, his thesis tended to have some support. (It was not absolute, even on those grounds. “Shovel incisors” have been found in older fossils from Kenya and the whole suite of morphological differences that Wolpoff ascribed to the Chinese fossils has suffered repeated challenges from several other researchers, even those who were not supporting the Out of Africa hypothesis.)

Didn’t Wolpoff have a student (Smith?) who went to Illinois and argued for a convergent theory in which the morphology was basically Mult-Regional, but the populations that developed continued to be augmented by the gene flow emanating from Africa? I am not sufficiently well-versed to defend or attack that scenario, either, falling back on my original point that the genetic flow appears, at this time, to most strongly support the Out Of Africa version.

Yes, Tom, Wolpoff did at the time have some students who had jumped ship after school, the convergent theory is exactly as you described it. Also, the list of Eve believers is long and distinguished including public personas such as Gould and Niles. I think this is perhaps why Eve gets so much attention, that and anything to do with genetics these days gets a lot of press. When I was at UofM in the mid 90’s bio-anthro had(as I mentioned)two distinct camps(the replacement theory is not new), with people who’s entire career has been invested in their idea…Chris Stringer and Wolpoff were already mortal enemies. When the genetic evidence(mitochondrial clock, first)came out, the replacemnet camp went wild Others looking at the evidence more objectively(as with any good science) discovered problems, contamination, etc. and the fact that maybe the geneticists went looking for a mitochondrial Eve, like I said, replacement has been around and very popular for a while, it was not invented by examining DNA evidence, but fossil evidence. Strange how two people can look at the fossil record and come to such different conclusions, but thats healthy scientific debate, things are unresolved and in a constant state of flux, I just wish someone would tell the editors and pogrammers of science media that.

oops, PROGRAMERS, this debate is not about Poland circa early twentieth century.