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Critical Thought & Religious Liberty

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Out of Africa vs. Multiregionalism

December 7, 1999

by Dr. Billings


A
ll anthropologist with few exceptions believe that the hominid line evolved only in Africa, and then spread out throughout the rest of the world. The focus of this debate however isnít where “humans” in the interchangeable sense of simply “hominids” evolved, but rather where did our specific subspecies, Homo sapiens sapiens (also referred to as “modern Homo sapiens” or “anatomically modern humans,” and I will use all three interchangeably) evolve?

Anthropologist are generally divided between two major models. On the one hand, you have the multiregionalist model, which states that hominids originally evolved in Africa, but after Homo erectus evolved and spread out to other parts of the Old World, modern Homo sapiens evolved from them in different parts of the world, namely Africa, Europe, and Eastern Asia, maintaining genetic continuity through extensive and frequent gene flow.[1]

The other popular model is the replacement model or “Out of Africa” hypothesis. It basically states that modern Homo sapiens evolved only in Africa and then spread out to populate the rest of the world, replacing other populations of hominids.[2]

Obviously both canít be correct, and the proponents of both furiously argue over who is correct. I made no understatement when I used the word “hotly” above, as this debate often sparks insult exchanges, and at one time, almost came to physical blows! There is one major proponent of each hypothesis, and each is the name first associated with each respective theory.

These two gentlemen, by the way, are the ones doing most of the insult exchanging, and have grown to literally hate each other, refusing to speak to one another. I will of course make many references to these two people, so I should probably introduce them. Milford Wolpoff, of the University of Michigan, is the leading proponent of the multiregionalist model, and Christopher Stringer, of the Natural History Museum in London is the leading advocate of the replacement model.

I have researched these two models extensively in the last couple of years. Iíve examined hundreds of back issues of science journals, researched new ones, visited dozens of internet sites, as well as read several books on the subject. I have drawn the conclusion that most anthropologist seem to be siding with the replacement model. Of course, it could be that the “out of Africa” advocates are just more vocal so that you hear more from them, but whatever the case, more and more authors are supporting the “out of Africa” model, both in books and journals. Of course, I have found that most donít seem to support an extreme version of the “out of Africa” model. There are some compromises that have been reached, such as, the idea that the original Homo sapiens sapiens evolved out of Africa, but that some limited gene flow that occurred afterwards during their expansion absorbed some of the other forms of Homo sapiens, adding variety within the species, without forming a new species.

Otherís maintain that the spread of modern Homo sapiens wasnít primarily a spreading of people, but of the genes that conveyed a selective advantage, which were absorbed by the rest of the world from Africa.

In fact, this is the position of one of Wolpoffís students, Fred Smith, from the Northern Illinois University. Smith embraces the “assimilation” hypothesis, which states that the fossil evidence does indeed favor Africa as an origin for modern Homo sapiens. From there, a small number of people passed the modern Homo sapiens genes to populations outside of Africa. The genes obviously grant a selective advantage, and were quickly spread to other Homo sapiens populations.[3] There would have been some replacement, but not enough to call it a “replacement” model, the main cause of Homo sapiens sapiens domination would be gene flow. This hypothesis does explain several problems on both sides, as we shall examine later.

The multiregionalist model canít just be pushed aside however, as it raises some valid points, that are seemingly contradictory to the “Out of Africa” model. I intend to show however, that the two can be reconciled to both best fit the evidence. Let us now examine the evidence, and see for ourselves where it points.

First of all, where are the oldest Homo sapiens sapiens fossils found? The Jebel Qafzeh skull from Israel is the most commonly known candidate for the oldest modern Homo sapiens skull ever found. Some debate exist over several archaic features, mainly the with respects to the the large nasal aperture, and slight browridges. All are acceptable variation within our subspecies however. The browridges, for example, are equal in size to the Kow Swamp specimen [seen here], which is only 9,000-13,000 years old, clearly making it a modern Homo sapien. One can see this by comparing the two, which one can do in the book: Human Origins: The Fossil Record, by C. Larsen, R. Matter, and D. Gebo (pp. 158, 180). The browridges are actually smaller in size than those on the Wadi Kubbaniya skull, which is also clearly a modern Homo sapiens, dating from 8 to 20 kya (Ibid, pp. 158, 162).

Clearly, these differences are acceptable, and in light of the evidence from the rest of the cranium, they are differences that must be accepted, because it is appears overall to be a modern Homo sapiens. It dates to between 92,000-115,000 years of age.[20]

Another even more debatable find, which possibly could be older than the Qafzeh specimen, is the Skhul 5 skull. The Skhul is also in Israel, and the site is divided into layers, and this cranium came from Layer B. Layer B gives dates ranging from 80,000-119,000 years of age.[4] So the Skhul 5 specimen might be as old as 120,000 years of age, which would make it as old, if not slightly older, than the Qafzeh skull.

Skhul 5 has several modern Homo sapiens features. It has a distinct chin for one. There is no bunning in the occipital. Dentally, it is a modern human as well. Itís mandible appears fully modern. It has a high forehead, and a rounded vault. It also has some Neandertal-type features however, such as mild prognathism in the mid-facial area. Itís teeth are proportioned like a Neanderthal as well. It appears to support a multiregionalist model, in that it suggest at least limited gene flow between the Neanderthals and the modern Homo sapiens in the area of the Middle East.

There are other candidates for the oldest Homo sapiens sapiens fossils ever found. The Omo I skull found in Ethiopia is dated to between 120,000 to 130,000 years of age, based upon U-S dating. It is said to be a modern Homo sapiens, based upon several features: the high, rounded skull, the distinct chin, itís skeletal frame, which was considerably taller and slimmer than other archaic forms, the rounded occipital region, and tiny browridges compared to other archaics (not to mention, I think I have demonstrated that several undisputedly modern human specimens have browridges as large or larger than the ones in question).[5] Other at least near modern Homo sapiens fossils have been cited by various paleoanthropologist as candidates for the oldest modern Homo sapiens found, such as LH-18, from the Ngaloba region in Tanzania, which has been dated to 120-130 kya.[6]

All of these sites are either in Africa or the Middle East. What of the rest of the Old World? What are the oldest fossils in other regions? Well, it is common knowledge in the paleoanthropological arena that anatomically modern Homo sapiens appeared in Europe about 40 kya, as a result of dating remains from the Cro-Magnon site in France.

In Australia, the oldest dated Homo sapiens sapiens fossil remains are the Lake Mungo I cremation remains, which date back to 24-30 kya. Dating of archaeological sites associated with modern Homo sapiens however has pushed that date to as early as 50,000 years ago. Modern Homo sapiens might have been in Australia thousands of years before they made it to Europe.

In Eastern Asia, the oldest confirmed date for a modern Homo sapiens fossil is about 20 kya, possibly 25 kya, based upon radiocarbon dating of skeletal remains. These finds are a small collection of modern Homo sapiens fossils, representing as many as five individuals, including mandibles, and both cranial and postcranial remains. They were found in Tabon, in the Philippines. Archaeological evidence from the Zhoukoudian Cave in China suggest modern Homo sapiens occupation in Eastern Asia as early as up to 30 kya, and a skull fragment from the Niah Cave in Borneo might be as old as 40,000 years of age, based upon the dating of charcoal that might be associated with the fossil.

These four places, Europe, Africa, Australia, and the Far East contain beyond argument the oldest fossils representative of modern Homo sapiens. The oldest remains clearly are found in Africa, or right outside of Africa, in the Middle East, and they come out in front by a long ways. With finds dating to clearly at least 100 kya, these fossils far surpass in age their counterparts found in the other countries, containing fossils that are double the age of even the oldest archaeological sites, never mind the actual fossils themselves.

But there also appears to be evidence that suggest that the multiregional hypothesis has some validity, particularly in Eastern Asia. The major bulk of the evidence comes from comparisons of Asian Homo erectus morphological traits with modern Chinese Homo sapiens traits. Anthropologist Franz Weideneich has composed a list of “regional features” linking Zhoukoudian Homo erectus features with modern Chinese features:

    –  midsagittal crest and parasagittal depression
    –  high frequency of metopic sutures
    –  high frequency of accessory bones that form within the cranial sutures
    –  Mongolian features in the cheeks
    –  exostoses of the mandible, ear, and maxillary femoral platymeria
    –  strong deltoid tuberosity of the humerus
    –  shovel-shaped incisors
    –  a horizontal course of the nasofrontal and frontomaxillary sutures
    –  rounded profile of nasal saddle and nasal roof
    –  rounded infraorbital margin
    –  reduced posterior teeth
    –  high frequency of third molar agenesis
    –  small frontal sinuses

There has been criticism of Weidenreichís list however. Colin Groves of the Australian National University has extensively examined these morphological features in various specimens, and questioned these claimed similarities. He notes that only some Chinese populations display these correlations, and most do not.[7] That is an anomaly that contradicts Weidenreichís hypothesis, but one finds oneself asking, what about the ones that do display these correlations? I will discuss how this can be reconciled later.

Another charge leveled at this list is the fact that all of these “regional features” are found on other fossils. In his book, The Neandertal Enigma: Solving the Mystery of Modern Human Origins, James Shreeve points out that all of these traits are found on fossils outside of China, some in Africa, far and removed from China. [8] The problem is, there arenít any fossils that display all of these features outside of China, so this still seems to offer support for the multiregionalist model, but some aspects, such as the objections raised by Groves, seem to support some degree of discontinuity, or at least some replacement. It could be that we have a combination of both to a degree, as I shall comment more on that later.

Chris Stringer argues that these features can be explained in ways other than a recent shared common ancestry. He has offered that these characteristics could be what he dubs “primitive retention,” features derived from a more distant common ancestor to all Homo sapiens sapiens, as opposed to only that region of the world alone.[9] Multiregionalist Geoffrey Pope concedes it is a possibility, citing the shovel-shaped incisors found on Homo erectus fossils in Kenya.[10]

Of course, one objection that comes to my mind is the possibility of parallel evolution between Homo erectus and modern Homo sapiens. It is very possible that the same environmental pressures that selected these traits in Homo erectus selected these same traits in Homo sapiens sapiens for the same reason. After all, it is a common evolutionary fact that creatures living in the same environment will likely have the same adaptations. An example would be the color of many arctic animals, like foxes, weasels and rabbits, who all have white coats as an adaptation to living in colder regions. A possible objection to this would be the lack of Homo sapiens sapiens with non-Asian features found in China. We know that the Inuits underwent adaptations that caused many easily noticeable structural changes that distinguish them from their Mongoloid ancestors in only a few thousand years, ranging from a change in stature and height to a massive increase in capillaries under the skin (so they can withstand thecold temperatures better, Inuits can withstand submergence in very cold water for lengths of time that would give any other human hypothermia). Apparently, such regional adaptations can occur virtually overnight on a geological time scale, in only several thousand years.

It is conceivable that we havenít found any fossils within such a short window of time. It is conceivable that there was no fossilization of these hypothetical newcomers during this short time.

The speculations abound however, without any supporting evidence. All are possibilities, so we canít discount the multiregionalistís evidence yet. The jury will have toremain out on this one.

There has been new research that further damages the multiregionalist model in its full form, supporting instead the “out of Africa” hypothesis. Researchers at the Institute of Medical Biology at the Chinese Academy of Medical Sciences (including J.Y. Chu, W. Huang, S.Q. Kuang, J.M. Wang, J.J. Xu, Z.T. Chu, Z.Q. Yang, K.Q. Lin, P. Li, M. Wu, Z.C. Geng, C.C. Tan, R.F. Du, and L. Jin) have done genetic studies similar to those done by Ray Suarez to demonstrate the Asian origin of Native Americans and those studies done to determine the degree of our relationship with the other great apes.

They extracted DNA samples either directly from lymphocytes or from cell linings. Data was collected, and phylogenies were constructed by using the neighbor-joining method. If the allele frequency distributions of the population for all microsatellite loci were available, the population was then submitted to phylogeny analysis. The results supported the “Out of Africa” hypothesis, showing that the Chinese separated from the African population recently, much more so than 1.8 million years ago, when Homo erectus first appears in Asia. Their conclusion is that:

“[I]t is now probably safe to conclude that modern humans originating in Africa constitute the majority of the current gene pool in East Asia. A phylogeny with very different topological structure would have been expected if an independent Asian origin of modern human had made a major contribution to the current gene pool in Asian populations.…The current analysis suggests that the southern populations in East Asia may be derived from the populations of Southeast Asia that originally migrated from Africa,…” [11]

Clearly this does not support the multiregional model, but explicitly supports the “out of Africa” model. The author of the above admits however that “the methods employed in this analysis can detect only major genetic contribution from particular sources, a haplotype-based analysis will probably detect minor contribution from an independent origin of modern humans in East Asia.” (ibid, p. 11766) I predict that if “a haplotype-based analysis” is performed, that they will indeed find minor genetic contributions from the East Asian population of hominids.

That is because there is a speculation I have that would solve the problems pointed out in the evidence for both models, and reconcile the two, at least in East Asia. What if the “out of Africa” model is correct, modern Homo sapiens did evolve in Africa, but when they migrated to China, there was a small amount of gene flow that provided the Asian-feature correlation we find between Chinese Homo erectus and some of the modern populations of China? Those Homo sapiens that didnít participate in this gene flow represent those Chinese populations that donít fit the aforementioned “regional features” correlation outlined by Weidenreich, but rather succumbed to the same selective forces that formed the Asian traits in the first place, acquiring many of the same traits that way, but not all of them.

They basically have the same Mongoloid design, but donít quite fit into Weidenreichís correlation. So basically, I propose a mixture of elements of both models, with gene flow occurring between some native populations and some African immigrants accounting for Weidenreichís correlation, parallel evolution accounting for those that donít, and the replacement of some of the previous Asian population mixed with an absorption of other Asian populations. This model would fit the evidence on both sides, and eliminates the problems of both.

There exist further genetic evidence for an African origin of modern Homo sapiens, and I find it is best explained in the context of Frank Smithís “assimilation” model, i.e. that it was modern Homo sapiens genes that migrated out of Africa via a small group of people, rather than a large group of people from Africa spreading out to conquer the world, as I shall demonstrate later.

One piece of evidence comes from similar, but admittingly less reliable test than the one just outlined performed by the Chinese. At the University of California in Berkeley, Allan Wilson, Rebecca Cann, and Mark Stoneking took DNA samples from the placentas of 147 women from various regions of the world and analyzed each womanís mitochondrial DNA. There studies showed virtually no variation among the mitochondrial DNA of all of these cultural and racial representatives, save only in Africa, where significant variation was found. This of course implies that Africanís have been evolving from a local ancestor for a lot longer since mitochonrdial DNA has existed, and have therefore accumulated more mutations in their mitochondrial DNA, and that the rest of the world evolved from one small, specific group, presumably from Africa or nearby, not long enough ago to have acquired significant variation through mutation. The Berkeley team went one step further, using a sort of genetic clock to determine that modern human mitochondrial DNA arose in Africa anywhere from 100 to 250 kya. [12]

This of course relies on accepting an average rate of mutations to perform the calculations with. It further assumes that the oldest fossils represent the first, so that the clock can be calibrated. Critics have been quick to point out that not only does the upper end of their date not match the fossil record, but that other reasonable rates of mutation and fossil reference points can be assumed that give dates back to 700 kya! Some have even went so far as to argue that one can analysis the data differently than the Berkeley team did and produce even more parsimonious results. At any rate, 700 kya is far off par with the fossil record, which shows modern Homo sapiens as dating back absolutely no later than 150 kya, and that is being liberal.

Personally, I reject molecular dating because of the unverifiable assumptions that must be made. Considering that a variety of possible rates can be reasonably employed and give dates ranging from 90 to 700 kya, it obviously isnít an accurate dating technique.

In all fairness however, the fact that the Berkeley teamís dates are highly questionable to say the least does not change the fact that the slight variation among the worldís population save only in Africa where such variation was extensive must be explained somehow. One canít confuse the parts of their research that produce valid points with those parts that are of no use at all.

Furthermore, there is no reasonable mutation rate that can produce the date that multiregionalists would require for the full and unedited version of their model to be correct, which would be a genetic dating of about 2 mya, when Homo erectus left Africa. The Berkeleyís team certainly havenít provided an adequate date for the migration from Africa, but they have shown that it occurred a lot sooner than the multiregionalist model requires, which would be the time when the migration of Homo erectus occurred. Alone, this evidence would be, I freely admit, questionable at least. It however is backed by the Chinese study, as well as several others.

A study performed by Professors Ken Kidd and Sarah Tishkoff at the university of Yale has offered similar evidence, albeit without any dating methods applied. They have examined nuclear DNA instead of mitochondrial DNA, and have found a peculiar marker in chromosome 12. Geneticist have long known that DNA consist mostly of “junk” sequences, those sequences that donít contribute to the present genetic makeup of an organism (but are probably evolutionary vestiges of a previous genetic makeup in an early organism from which the present one evolved). Dr. Kidd has discovered that in a sequence of this junk DNA, once again, found in chromosome 12, there exist a section of a base sequence that consist of five basis: CTTTT.

In all humans throughout the world sampled, there exist either a sixfold repetition of this section, or a deletion of it all together. Those two options seem to be all that is found. In Africa however, this section can be deleted, or it can be repeated up to fifteen times, with every numerical variation between.[13] Just like the Berkeley research, this research implies that the African population has had more mutations in this genetic section accounting for this variation, and hence have been evolving from a common ancestor longer than the rest of the world, who appear to have evolved relatively recently from a common ancestor.

Similar test were conducted by James Wainscoat, a geneticist at Oxford. Wainscoat and his colleagues examined the haplotypes in eight diverse human populations, ranging from Europe, Africa, Asia, New Guinea, and to the South Pacific. They found that two of the gene forms were extremely common in Africans, but not in the rest of the world. Is this a trend here?

It appears so. Once more, we have indications that one continent is the origin for all modern humans, and this continent appears to be Africa. In Wainscoatís words: “Our data is consistent with a scheme in which a founder population migrated from Africa and subsequently gave rise to all non-African populations.” He goes on to indicate that it might have only been a few hundred people.[14]

No matter what criticism is leveled at any one of these genetic test, the fact remains that all genetic testing on the subject has 100% unanimously supported the “out of Africa” hypothesis.

This is something that the multiregionalist simply cannot continue to ignore. They have to be willing to compromise. It is the same as their situation with Weidenreichís “regional features” lists. Taken individual, each feature is highly debatable and is evidence for nothing. Taken in totality, they are a formidable obstacle to the strict replacement model. The same holds true here. Viewed as a whole, they are a formidable obstacle to the multiregionalist that they must address. Somehow, their theory must accept that there was indeed an ultimate origin of our subspecies in or around Africa. Again, compromise is inevitable. Neither model can continue to exist in its strictest form, and both are necessary to adequately explain the development of modern Homo sapiens.

Another thing that must be considered as well is the fact that each region included in the multiregionalist scheme must be examined individual. We cannot interpret evidence for predicted gene flow in the multiregionalist hypothesis occurring in one region as being evidence that the same occurred in another. So we shall now turn to Europe, where I think we will find that the same compromises necessary to reconcile the two models in Asia is necessary in Europe.

One piece of evidence offered by many for the ďout of AfricaĒ model is the uniform presence of Aurignacian technologies, which developed all over Europe about 45 to 35 kya (suspiciously right before the Neandertalís disappeared), extending from the western border through central, eastern, and southern Europe, as well as into the northern portion of the Near East. This new technology is associated with modern Homo sapiens, but not with Neandertalís. There are two possibilities: The situation reflects the immigration into the land of the modern Homo sapiens or the emerging, independently, of the technology from within each area in the region from previous populations of Neandertals.

The former tends to be favored by Old World archaeologist. Four observations are offered to support this conclusion:

–  The technology is uniformly spread over an extremely large area of the continent, including almost all of it. This cultural uniformity is not similar to the varied technologies displayed by the Neandertal throughout the rest of their long history (which is the largest part of their existence). This implies that the Neandertalís didnít have the connection with the rest of their kind that the Homo sapiens sapiens did. Their cultural uniformity probably was one of the factors leading to eventual domination by Homo sapiens.

–  The Arignacian technology appears so suddenly without any clear local antecedents that a local European origin for the technology cannot be supported. It isnít valid to conclude that such technology arose without a logical predecessor from the varied (and more primitive) technologies used during the Middle Paleolithic. Most archaeologist believe that the Middle East is the origin of this technology.

–  It is generally accepted by all paleoanthropologist and archaeologist that this technology appeared in Europe around 45-35 kya. Radiocarbon dating demonstrates an increase of older to younger dates going from east to west across Europe, implying the technology developed outside of Europe, to the east, and was brought into Europe, where it was carried across it to the west coast.

–  It is further accepted that the Aurignacian technology encompasses the earliest known occurrences of most of the advances associated with the Upper Paleolithic, and that such a spread of technological revolutions couldnít have been accomplished without a complex and highly structured language among the people producing the technology. This trait is debatable in Neandertal, but known to be a trait of modern Homo sapiens. [15]

If the Aurignacian technologies was developed by modern Homo sapiens, and if dating of the technologies has shown that the technologies were brought in from the East, that implies that modern Homo sapiens didnít arise in Europe from the Neandertals there, but rather that they came into Europe already evolved to a modern form. Furthermore, Glenn Conroy comments that “in both Africa and the Middle East, modern human populations first appear in association with Middle Paleolithic (Middle Stone Age) industries.” He further states that “[i]n Europe the transition from Middle to Upper Paleolithic assemblages occurred about 45,000 to 35,000 years ago, much later than in both Africa or western Asia(Near East).” [16] This demonstrates that modern Homo sapiens had evolved before the Aurignacian technology had even been invented.

It further acts as evidence that modern Homo sapiens had existed a long time before they came to Europe, since the technology they existed in association with predated the same technology in Europe by many thousands of years. As just noted in the sentence before this, they had to have been here even longer, since their earliest remains are associated with technologies that existed before the late Paleolithic era.

It seems that the either Africa or the Middle East was the birthplace of this Aurignacian technology, and by extension, the birthplace of modern Homo sapiens. It further seems that they existed in these areas for quite a while before venturing into Europe. If that is the case, they couldnít have possibly evolved from European Neandertals.

Evidence suggest they didnít evolve from Israeli Neandertals either. The earliest dates for Neandertals in Israel are positively fixed at 40 kya, and could be as old as 60 kya. Flints and teeth associated with modern Homo sapiens finds in the area give dates around 100 kya, anywhere from 40 to 60 thousand years before the Neandertal were present. [17] Morphological traits further betray it as an unlikely possibility that modern Homo sapiens in Israel evolved from Neandertals, as will be covered in my next examination of the evidence.

There exist morphological traits associated with modern Homo sapiens remains in Europe and the Middle East that further imply an African origin, or at least an origin in a different climate than Europe, and from predecessors that werenít the Neandertals. In Europe we see the preadaptive fossils that are lacking in the far east. There is of course the obvious, the modern Homo sapiens, even the earliest of them, in both Europe and the Middle East are all far more gracile than the Neandertal. We see no transition from the bulky build of the Neandertal to the gracile built Homo sapiens sapiens in either region, only a sudden appearance of gracile beings living along side the Neandertals. Gracile traits are expected however in Homo sapiens from Africa however, and the Middle East. More specific and informative morphological traits can be examined as well.

Anthropologist Erik Trinkaus did research into the tibia (shinbone) to femur (thighbone) ratio of modern Homo sapiens found in Europe and the Middle East. He did this to shed light on the controversy, as he knew that the ratio of the tibia to the femur is proportional to the climate of the individual. [19]

The shinbone of an Inuit is about 81% of the length of the thighbone. The shinbone of a Masai is about 87% of the length of the thighbone. This ratio can act as a thermometer to tell the approximate average temperature of the climate in which an individual evolved, or at least where the individuals ancestors evolved. This is because individuals in colder climates tend to have more compact builds, which include a shorter ratio of the lower arm to the upper arm, as well as a shorter ratio of the tibia to the femur. [19]

When Trinkaus examined Neandertals from both Europe and the Middle East, he found the tibia was about 79% of the femur in length. That is exactly about what we would expect, considering the climate they developed in. Those specimens in the Middle East had not been there long enough to lose this adaptation to cold weather.

Examinations of the earliest modern Homo sapiens from Europe and the Middle East showed that the tibia was about 85% the length of the femur, more similar to a Masai warrior than to a Neandertal. This acts as fairly powerful evidence that not only did modern Homo sapiens not evolve from the Neandertals (we would expect the earliest modern Homo sapiens to have the same tibia to femur ratio as the Neandertals), but also that they evolved in a warm, tropical climate, such as offered by Africa. Even the Middle East would be a good candidate. Europe however was obviously not a cradle for modern Homo sapiens however.

There is another morphological trait that has been examined by Christopher Stringer that implies that modern Homo sapiens didnít evolve from Neandertal. He notes that Neandertals had large, broad noses. They further had huge spaces inside the cheekbones, the sinuses. Modern humans have them as well, but the Neandertals were significantly larger. Multiregionalist point out that modern Europeans have large, broad noses as well, albeit it not the large sinus cavities. They cite this as a case similar to the Asian correlationís drawn by Weidenreich. Fortunately for us, we have fossils of the earliest modern Homo sapiens in Europe, and can check to see if these particular Europeans shared the nose of the Neandertal and modern Homo sapiens of Europe. Stringer measured the width of the nasal cavity, as well as the distance between the base of the nasal cavity and the point between the eyes, and found that “while Neandertals and modern Europeans are, indeed, somewhat similar, Cro-Magnons—the supposed descendants of Neanderthals, according to the multi-regional hypothesis—again stood out has different. They had relatively smaller, flatter noses than either the Neanderthals or modern Europeans.” [18]

Stringer goes on to explain the fact that modern humans now in Europe have similar noses to the Neandertal as a case of parallel evolution. I agree this is a very good explanation, but I think there is more too it than that. I definitely agree that he has provided yet more evidence that Neandertal didnít produce modern Homo sapiens. However, I donít think parallel evolution alone explains all of the loose ends. Certainly, modern Homo sapiens in Europe would have evolved similar noses to the Neandertals even if they started out without them, due to the similar environmental pressures, as well as the similarities between the two sub-species or species, depending on how you want to classify the two groups. (and of course weíd expect that similar environmental pressures would be felt that much more by members of the same or similar species).

However, there are more pieces missing from the puzzle, that parallel evolution isnít going to explain away. Some Israel finds, such as the Skhul V specimen, have Neandertal features as well. They didnít live in the cold climates in which the Neandertal evolved, so they wouldnít have felt the same environmental pressures, and further didnít live there as long as modern Europeans have lived in Europe before they gained these traits. There had to have been some gene flow between the two populations, albeit it slight, since the gene flow wasnít able to produce a middle ground between Neandertal and modern Homo sapiens in the end, rather the modern Homo sapiens traits have come out as dominant. Skull V was probably a hybrid of the time, as it obviously wasn't a reflection of evolutionary trends.

But what of the compelling evidence that Neandertals didnít give rise to modern Homo sapiens? The only answer is that there was gene flow between the populations that occurred after the rise of modern Homo sapiens. This would be expected if the journey out of Africa occurred as Smith hypothesizes, via the genes more so than via literal large groups of people. Clearly this leaves the strict version of the replacement model that allows no gene flow out in the cold. It has no hope of surviving in this form, the evidence wonít allow it. The evidence however cannot be ignored for an ultimately African origin though, so the multiregionalist model wonít survive in itís current form either.

One additional problem with the multiregionalist model is the assumption that much and frequent gene flow occurred between evolving populations from Homo erectus to fully modern Homo sapiens in both Asia and Africa. This alone makes the model unparsimonious, not to mention the total lack of evidence (and unlikely nature) for the assumption. In fact, this is such a large lack of evidence, that it acts as evidence in of itself. The period between Homo erectusí first appearance in the Far East until the rise of somewhat recognizable modern Homo sapiens is a period that is a virtual ghost town for the area between the Middle East and the orients.

For a period of over one and a half million years, there are no Homo erectus fossils found in this area.

The only hominid specimen found in this area during this period dates to 150 kya, and that was an early archaic Homo sapiens specimen found in India.

With such a large absence of fossil evidence during this time, one can hardly argue that large populations filled the area between the areas of the Middle East and the orients necessary for this extensive and frequent gene flow. I could sympathize if there was a ten thousand year gap, with the chances of fossilization being so slim in the first place, that would be understandable (if curious in of itself). A hundred thousand year gap would make the claim highly suspect, and could not be viewed as being supported by evidence. A gap of over a million years is unbelievable. To think that this area was so densely populated to allow the significant gene flow required for the multiregionalist model is unthinkable. Clearly, there was no extensive gene flow, at least for the larger part of Homo erectusí existence as a species.

There is no way then that the Asian hominids could have stayed on course with the African variety in a continuous manner without this gene flow, and either one of three things would have occurred: either both groups would diverge from each other over time, one group would diverge while the other changed very little, or neither group would undergo much evolution. The latter possibility clearly isnít the case, as hominids did evolve from Homo erectus. Either of the other two cause problems, as speciation would be expected over such a large period of time.

If either group diverged from the other over a period greater than a million years, changes would have accumulated that would either have lead to speciation beyond the capability to interbreed, or would have lead to such morphological changes that interbreeding wouldnít be as desirable as breeding with those more similar. Let's face it, very few of us modern Homo sapiens would have been attracted to the Neandertal, and they were separated from us only by a few hundred thousand years.

Such attitudes would probably limit gene flow between regionally divergent populations, but it wouldnít eliminate it by any means. It would still exist, as such gene flow occurred during the era of United States slavery, and as in that case, it would cause noticeable effects. So if modern Homo sapiens evolved in Africa and spread out through the rest of the Old World, weíd expect to see slight influences from other hominids that were able to interbreed with the modern humans.

Such slight influences could result in the partial correlation outlined by Weidenreich, or the similarity of modern European noses to Neandertal noses, as well as the slight Neandertal traits of the Skhul V skull and other similar finds. This merging of the two models also eliminates the problems of both.

There is still one complaint of the replacement model that is offered by the multiregionalist, and that is that the "Out of Africa" advocates have no clearly defined mechanism for replacement.

Some advocates of that model have suggested that modern Homo sapiens were simply better equipt to survive, more efficient and simply out-competed the other hominids.

If one accepts Smithís model, it becomes clear that while some replacement occurred, much of the eradication of other hominids is attributed to genetic absorption. Smithís hypothesis raises a question of itís own however, and that is: Why were the modern Homo sapiens genes favored to such a large degree over the genes of the other hominids?

One possible answer of course is that they simply conveyed that large of an advantage. The issue of how other hominid abilities compared to modern Homo sapiens abilities is hotly debated.

Some hold to the position that the difference of ability wasnít great enough to justify the idea that modern Homo sapiens genes were simply that much more superior to the other hominids, but I think it is clear that they were.

While there are debatable examples of art prior to modern Homo sapiens development, and there are even undeniable examples from the Neandertals, there is no question that artistic examples increased at an incredible rate after the appearance of modern Homo sapiens. Art in of itself isnít helpful for survival, but it indicates a very highly developed abilitiy for abstract thought, correlated with high intellegence, which would have been highly advantageous.

Furthermore, it is undeniable that the archaic versions and the Neandertal didnít have the degree of brain power possessed by modern Homo sapiens. When I took paleoanthropology, my professor, Mark Hartmann, of the University of Arkansas in Little Rock, Arkansas, was fond of correctly pointing out that even the earliest versions of undeniably modern Homo sapiens had the same mental capabilities as ourselves, albeit they were more ignorant.

He also, most likely correctly, once commented during a lecture on Neandertals that there were “probably no rocket scientist” among the Neandertal, facetiously making the point that even the smartest Neandertals donít match our caliber of intellectual capabilities. Furthermore, it is highly debatable that Neandertals had the same abilities of fully modern speech that we do, and even if they did, that they had the complexity of language that we possess and employ. If modern Homo sapiens did have superior communication abilities (and the uniformity of the Aurignacian technologies, and the lack of the same among Neandertal technologies, implies a superiority of Homo sapiens communication and organization over the Neandertal), then they most certainly would have had a selective advantage that would have quickly taken root in the gene pool.

In light of all this, I think much can be said of the claim that Homo sapiens genes conveyed a significant advantage over other hominid genes of the era. Furthermore, it is highly likely that the modern Homo sapiens used their superior intellectual abilities to select themselves, albeit not consciously, through superior survival skills and possibly even the undermining of Neandertal survival activities, from simple competition to outright raids in a few cases (granted, I donít see this one example as being a major contributor!).

All of that aside however, we find evidence that replacement has occurred beyond question to some hominids. Surely even the most extreme multiregionalist wouldnít argue that all Homo erectus populations contributed to the modern human gene pool. Some had to simply have become extinct. Evolution isnít a changing straight line, but rather a branching off of new lines from old ones.

The entire species of Homo erectus didnít evolve into Homo sapiens, but only certain populations. It seems most logical to assume that most Homo erectus populations didnít contribute genetically to the modern Homo sapiens, but rather became extinct. There would only be two reasons for extinction: the usual environmental changes that a species canít adapt to match, or competition from another species that causes extinction. The first option isnít likely, in light of the fact that Homo erectus was without a doubt the most successful of all the hominids, existing the longest and over a large range, with a variety of environments. Their two-million years of existence saw a large range of environmental change which they easily survived, and from their extinction to the present date, there hasnít failed to be at least a few places within their range where the environment has been suitable for the survival of Homo erectus. No, environmental factors alone cannot account for the extinction of Homo erectus.

The only other alternative is replacement by superior Homo sapiens, modern or otherwise. Another undeniable example is the robust Australopithecine. They most certainly did not contribute to the modern Homo sapiens gene pool, but are agreed by all paleoanthropologist to be an evolutionary dead end. It is obvious that they were replaced by superior hominids, probably due to the specialized diet they evolved to live on. When competition entered the arena, they couldnít compete and were selected out of existence. For whatever reasons that Homo erectus and the robust Australopithecine were replaced by other, superior hominids, those reasons could serve as precedents for at least a large replacement of other hominids by modern Homo sapiens.

So in summary, I think the best explanation of all of the evidence is to adopt the model that modern Homo sapiens evolved either in Africa or in the Middle East, and that they spread out, mostly genetically and not literally, to the rest of the world, engaging in limited gene flow with other hominid populations they encountered, resulting in an absorption of a large percentage of the invaded populations, with the rest eventually succumbing to replacement by the superior modern Homo sapiens.

Clearly my idea will not be embraced by all, and the debate will continue. Iím sure it wonít be resolved anytime soon, possibly not in my lifetime. One thing is abundantly clear however, and that is that neither model as is will adequately explain all of the evidence, and that both in their extreme and unedited forms have fatal problems that will result in neither surviving in their present form. A compromise between the two is necessary for us to journey closer to the truth of the origins of the modern Homo sapiens, as well as the disappearance of the other varieties of Homo in such a relatively short period of time.


Bibliography

  1. Caspari, R. and M. Wolpoff. Race and Human Evolution. New York: Simon & Schuster. 1997. p. 11.

  2. McKie, Robin and Christopher Stringer. African Exodus: The Origins of Modern Humanity. New York: Henry Holt and Company. 1996. p. 14.

  3. Donnelly, S.M., A.B. Falsetti, F. Smith. “Modern Human Origins.Ē Yearbook of Physical Anthropology 32 (1989): 35-68.

    Smith, F. “Upper Pleistocene Hominid Evolution in South-Central Europe: A Review of the Evidence and Analysis of Trends.” Current Anthropology 23 (6 1982):667-687.

    Smith, F. H., F. Spencer, eds. The Origins of Modern Humans. New York: Alan R. Liss, Inc. 1984.

  4. Conroy, G. Reconstructing Human Origins: a Modern Synthesis. New York: W.W. Norton. 1997. pp. 439-440.

  5. Leakey, R. ďEarly Homo sapiens remains from the Omo river region of south-west Ethiopia: Faunal remains from the Omo ValleyĒ Nature 222 (1969): 1132-1133.

  6. Conroy, G. ibid, pp. 41-413

    Stringer, C. ibid, p. 156

  7. Groves, C.P. ďA regional approach to the problem of the origin of modern humans in Australasia.Ē The Human Revolution. Eds. P. Mellars, C. Stringer. pp. 274-285.

  8. Shreeve, J. The Neandertal Enigma: Solving the Mystery of Modern Human Origins. New York: Avon Books. p. 99.

  9. Stringer, C. “The emergence of modern humans.” Scientific American Dec. 1990: 98-104.

  10. Pope, G. ďEvolution of the Zygomaticomaxillary Region in the Genus Homo and its Relevance to the Origin of Modern HumansĒ Journal of Human Evolution 21 (1991): 189-213

  11. Tan, J. “Genetic relationship of populations in China.” Proceedings of the National Academy of Science Vol. 95, Sept. 1998: 11763-11768.

  12. Cann, R., M. Stoneking, and A. Wilson. “Mitochondrial DNA and Human Evolution.” Nature 325 (1987): 31-36.

  13. Mckie, R. & Stringer, C. African Exodus: The Origins of Modern Humanity. New York: Henry Holt & Company. 1996. pp. 132-134.

  14. Wainscoat, J. S., et al. “Evolutionary Relationships of Human Populations from an Analysis of Nuclear DNA Polymorphisms.” Nature 319 (6 1986): 491-493.

  15. Conroy, G. ibid, p. 429.

  16. ibid, p. 428.

  17. Aitken, M., H. Valladas. “Luminescence dating relevant to human origins.” Eds. M. Aitken, C. Stringer, and P. Mellars. op. cit. R. Grun, & C. Stringer. “Electron spin resonance dating and the evolution of modern humans.” Archaeometry 33 (1991): 153-199.

  18. Stringer, C. “The origin of early modern humans: a comparison of the European and non-European evidence.” The Human Revolution. Eds. P. Mellar and C. Stringer. Edinburgh: Edinburgh University Press. 1989. pp. 232-244.

  19. Trinkaus, E., “Neanderthal Limb Proportions and Cold Adaptation.” Aspects of Human Evolution. Ed. Stringer, C. London: Taylor & Francis. 1981. pp. 187-224.

  20. Larson, C.S., R.M. Matter, D.L. Gebo. Human Origins: The Fossil Record. Illinois: Waveland Press, Inc. 1998. p. 158.