Out of Africa vs. Multiregionalism
December 7, 1999
by Dr. Billings
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 isn’t 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 can’t 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. I’ve 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 don’t 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.
Other’s maintain that the spread of modern Homo sapiens wasn’t
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 Wolpoff’s 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 can’t 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. It’s 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. It’s
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, it’s 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 Weidenreich’s 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 Weidenreich’s 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 aren’t 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 haven’t 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 can’t discount the multiregionalist’s
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 didn’t participate in this gene flow represent those
Chinese populations that don’t 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 don’t quite fit
into Weidenreich’s 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 Weidenreich’s
correlation, parallel evolution accounting for those that don’t, 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 Smith’s “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 woman’s 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 African’s 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 isn’t an accurate dating technique.
In all fairness however, the fact that the Berkeley team’s dates are
highly questionable to say the least does not change the fact that the
slight variation among the world’s population save only in Africa where
such variation was extensive must be explained somehow. One can’t 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 Berkeley’s team
certainly haven’t 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 don’t 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
Wainscoat’s 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 Weidenreich’s “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 “out of Africa” model is
the uniform presence of Aurignacian technologies, which developed all over
Europe about 45 to 35 kya (suspiciously right before the Neandertal’s
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 Neandertal’s. 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 Neandertal’s didn’t 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 isn’t 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 couldn’t 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 didn’t 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 couldn’t have possibly evolved from European Neandertals.
Evidence suggest they didn’t 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 weren’t 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
didn’t 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
correlation’s 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 didn’t produce modern Homo sapiens. However, I
don’t 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 we’d 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 isn’t going to explain away. Some Israel finds, such as the
Skhul V specimen, have Neandertal features as well. They didn’t live in
the cold climates in which the Neandertal evolved, so they wouldn’t have
felt the same environmental pressures, and further didn’t 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 wasn’t 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 didn’t 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 won’t allow it. The evidence
however cannot be ignored for an ultimately African origin though, so the
multiregionalist model won’t survive in it’s 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 erectus’ 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 erectus’
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 isn’t 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 wouldn’t 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 wouldn’t 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, we’d 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 Smith’s model, it becomes clear that while some
replacement occurred, much of the eradication of other hominids is
attributed to genetic absorption. Smith’s hypothesis raises a question
of it’s 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 wasn’t 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 isn’t 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 didn’t 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 don’t 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 don’t 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
wouldn’t argue that all Homo erectus populations contributed to
the modern human gene pool. Some had to simply have become extinct. Evolution
isn’t a changing straight line, but rather a branching off of new lines from
old ones.
The entire species of Homo erectus didn’t evolve into Homo
sapiens, but only certain populations. It seems most logical to assume
that most Homo erectus populations didn’t 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 can’t adapt to match, or competition from another species that
causes extinction. The first option isn’t 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 hasn’t 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 couldn’t 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.
I’m sure it won’t 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.
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