out of africa (or not) the incredibly complex and mostly true story of the origin and dispersal of...

Out of Africa (or not)Out of Africa (or not)

The incredibly complex and mostly The incredibly complex and mostly true story of the origin and dispersal true story of the origin and dispersal

of of Homo sapiensHomo sapiens throughout the throughout the World.World.

There are currently two There are currently two competing theories of the origin competing theories of the origin

of anatomically modern of anatomically modern Homo sapiensHomo sapiens

The The Replacement modelReplacement model, which states that , which states that there was a single origin for Homo sapiens there was a single origin for Homo sapiens (in Africa), and these anatomically modern (in Africa), and these anatomically modern humans subsequently radiated out from humans subsequently radiated out from Africa and replaced other species of Africa and replaced other species of HomoHomo as they came in contact with them as they came in contact with them throughout Europe and Asia.throughout Europe and Asia.

The The Regional ContinuityRegional Continuity modelmodel, which , which states that modern states that modern Homo sapiensHomo sapiens developed from regional populations of developed from regional populations of archaic archaic Homo sapiensHomo sapiens populations that in populations that in turn evolved from regional populations of turn evolved from regional populations of Homo erectusHomo erectus..

The The replacement modelreplacement model of Christopher Stringer and of Christopher Stringer and Peter Andrews proposes that modern humans evolved Peter Andrews proposes that modern humans evolved from archaic from archaic Homo sapiensHomo sapiens 200,000-100,000 years ago in 200,000-100,000 years ago in Africa and then some of them migrated into the rest of Africa and then some of them migrated into the rest of the Old World replacing all of the Neanderthals and the Old World replacing all of the Neanderthals and other late archaic other late archaic Homo sapiensHomo sapiens. If this interpretation . If this interpretation of the fossil record is correct, all modern people share of the fossil record is correct, all modern people share relatively modern African ancestry. All other lines of relatively modern African ancestry. All other lines of humans that had descended from humans that had descended from Homo erectusHomo erectus presumably became extinct. From this view, the presumably became extinct. From this view, the regional anatomical differences that we see among regional anatomical differences that we see among humans today are recent developments--evolving only in humans today are recent developments--evolving only in the last 50,000-40,000 years. This hypothesis is also the last 50,000-40,000 years. This hypothesis is also referred to as the referred to as the out of Africaout of Africa and the and the Noah's arkNoah's ark model.model.

The The regional continuityregional continuity (or multiregional) model of (or multiregional) model of Milford Wolpoff at the University of Michigan proposes Milford Wolpoff at the University of Michigan proposes that modern humans evolved more or less that modern humans evolved more or less simultaneously in all major regions of the Old World simultaneously in all major regions of the Old World from local archaic from local archaic Homo sapiensHomo sapiens populations. For populations. For example, modern Chinese are seen as having evolved example, modern Chinese are seen as having evolved from Chinese archaic from Chinese archaic Homo sapiensHomo sapiens and ultimately from and ultimately from Chinese Chinese Homo erectusHomo erectus. This would mean that the . This would mean that the Chinese and some other peoples in the Old World have Chinese and some other peoples in the Old World have great antiquity in place. Advocates of this model believe great antiquity in place. Advocates of this model believe that the ultimate common ancestor of all humans was that the ultimate common ancestor of all humans was Homo erectusHomo erectus in Africa more than a million years ago. in Africa more than a million years ago. Since then, however, it is proposed that there was Since then, however, it is proposed that there was sufficient gene flow between Europe, Africa, and Asia to sufficient gene flow between Europe, Africa, and Asia to prevent reproductive isolation and the subsequent prevent reproductive isolation and the subsequent evolution of distinct regional species. evolution of distinct regional species.

Regional Continuity Model Replacement Model

Obviously, whether you believe in one theory or Obviously, whether you believe in one theory or the other has a great impact on the question of the other has a great impact on the question of early dispersal and migration of early dispersal and migration of Homo sapiensHomo sapiens. .

The replacement model necessitates long The replacement model necessitates long distance dispersal and migration and adaptation distance dispersal and migration and adaptation to new environments, and the multi-regional to new environments, and the multi-regional model suggests in situ development and model suggests in situ development and adaptation over a longer period of time.adaptation over a longer period of time.

The following figure is a family tree for the The following figure is a family tree for the phylogenetic Class Primates. Although phylogenetic Class Primates. Although somewhat out of date, it does give an idea of the somewhat out of date, it does give an idea of the closeness of genetic relationships among the closeness of genetic relationships among the different families and the approximate timing of different families and the approximate timing of their divergence from the trunk of the primate their divergence from the trunk of the primate family tree. Although there is at least one big family tree. Although there is at least one big problem with this particular diagram that might problem with this particular diagram that might cause a skeptic to question the veracity of the cause a skeptic to question the veracity of the whole thing.whole thing.

See if you can spot the problem…See if you can spot the problem…

(Hominoidea)(Hominidea)

Yikes!

Showing Modern humansas different branches is not accurate--we’re all the same species

Dispersal corridors opened out of Africa and across the Middle East into South and East Asia during the late Pliocene. Corridors formed primarily along coastal land masses, the product of expanding polar ice caps and resultant drop in sea-level. Incipient development of the Red Sea rift also established departure routes through the Middle East. The drop in sea level in island Southeast Asia would have connected Sumatra, Java and Borneo with the mainland. Evolutionary analysis of fossil species indicates that large mammals dispersed along these routes sporadically during the late Pliocene and early Pleistocene. New fossil finds suggest that early Homo arrived in Asia some 1.8 to 1.9 million years ago, after departing Africa at least 100,000 years earlier.

Hominids now known as Homo erectus were found on Java, Indonesia, in 1891, and at Zhoukoudian, near Beijing, in the 1930s. As Homo erectus was clearly more primitive than hominid fossils known in Europe, human beings were initially thought to have emerged in East Asia and dispersed westward. Since the early 1960s, numerous fossils from African localities in the eastern Rift Valley, Lake Malawi and South Africa have demonstrated an African emergence for Homo . In the 1990s, advances in dating methods and new finds at Dmanisi (Georgia), Riwat and Pabbi Hills (Pakistan), Sangrian and Mojokerto (Java) and Longgupo (China) show that early Homo had arrived in East Asia by just after 2 million years ago. The following map shows dispersal corridors that would have been available due to lowered sea level in the at the Pliocene-Pleistocene boundary.

According to the Replacement Model, there is little question According to the Replacement Model, there is little question that that HomoHomo sapienssapiens emerged in Africa, although the date of emerged in Africa, although the date of emergence, the technological associations and the dates for its emergence, the technological associations and the dates for its Eurasian dispersals are debatable. Eurasian dispersals are debatable. Homo sapiensHomo sapiens originated originated between 200,000 and 100,000 years ago, somewhere in sub-between 200,000 and 100,000 years ago, somewhere in sub-Saharan Africa. Some recent discoveries in Zaire of ancient Saharan Africa. Some recent discoveries in Zaire of ancient and finely crafted tool types (such as barbed-bone harpoons) and finely crafted tool types (such as barbed-bone harpoons) indicate that the technology associated with this emergence indicate that the technology associated with this emergence may have been very advanced indeed, resembling the much may have been very advanced indeed, resembling the much later Upper Paleolithic of Europe. In the Levant, where later Upper Paleolithic of Europe. In the Levant, where HomoHomo sapienssapiens is evident about 90,000 years ago, a more archaic is evident about 90,000 years ago, a more archaic Middle Paleolithic technology still held sway. Consequently, Middle Paleolithic technology still held sway. Consequently, we may not yet say whether the European dispersal of we may not yet say whether the European dispersal of HomoHomo sapienssapiens was associated with either its emergence or a new was associated with either its emergence or a new technology.technology.

Genetic Evidence for the Genetic Evidence for the Replacement ModelReplacement Model

Mitochondrial DNAMitochondrial DNA

Y chromosomal DNAY chromosomal DNA

Mitochondrial DNA Mitochondrial DNA

Mitochondrial DNA offers a quick-ticking molecular clock Mitochondrial DNA offers a quick-ticking molecular clock and by comparing the number of mutations that have and by comparing the number of mutations that have collected in separate populations, geneticists can infer when collected in separate populations, geneticists can infer when the populations split from each other. the populations split from each other.

When selected sequences of mtDNA from a group of people When selected sequences of mtDNA from a group of people representing African, Asian, Australian, Caucasian and New representing African, Asian, Australian, Caucasian and New Guinean ethnic groups were compared, 133 variants of Guinean ethnic groups were compared, 133 variants of mtDNA were found. When these different mitochondrial types mtDNA were found. When these different mitochondrial types were arranged into an evolutionary tree, that tree showed a were arranged into an evolutionary tree, that tree showed a trunk splitting into two major branches. trunk splitting into two major branches.


One branch consisted only of Africans, the other included One branch consisted only of Africans, the other included some modern Africans and some people from everywhere some modern Africans and some people from everywhere else. The first branch represents the first modern humans and else. The first branch represents the first modern humans and forms the trunk and longest branch of the tree. The second forms the trunk and longest branch of the tree. The second branch represents a subgroup of modern humans that left branch represents a subgroup of modern humans that left Africa and later spread out to the rest of the world. Africa and later spread out to the rest of the world.


It was also found that all of the mtDNA (even from far It was also found that all of the mtDNA (even from far regions of the world) was similar. This suggested that the regions of the world) was similar. This suggested that the molecular clock has not been ticking long enough to molecular clock has not been ticking long enough to accumulate appreciable differences in our DNA. In other accumulate appreciable differences in our DNA. In other words, our species is young. words, our species is young.

But the African samples had the most mutations. This too But the African samples had the most mutations. This too implied that the African lineage is the oldest, that all modern implied that the African lineage is the oldest, that all modern humans trace their roots back to Africa.humans trace their roots back to Africa.

Map illustrating the timing of the migration of anatomically modern Homo sapiens out of Africa, based on mtDNA evidence.


An international study of Y chromosomal DNA shows that An international study of Y chromosomal DNA shows that East Asian populations migrated out of Africa and suggests East Asian populations migrated out of Africa and suggests that little or no interbreeding of that little or no interbreeding of Homo erectusHomo erectus and and Homo Homo sapienssapiens occurred after the migration. occurred after the migration.The goal of the study was to test the hypothesis that the The goal of the study was to test the hypothesis that the common origin of human populations is in Africa, and also to common origin of human populations is in Africa, and also to see if there was evidence of archaic admixture of see if there was evidence of archaic admixture of Homo Homo erectuserectus and and Homo sapiensHomo sapiens..


The researchers tested 12,127 male individuals from 163 East The researchers tested 12,127 male individuals from 163 East Asian populations. The Y chromosome was used because it Asian populations. The Y chromosome was used because it remains the same when passed from father to son. The Y remains the same when passed from father to son. The Y chromosome is was examined because it does not recombine, chromosome is was examined because it does not recombine, and so a lot more evolutionary information is available than is and so a lot more evolutionary information is available than is found in mitochondrial DNA.found in mitochondrial DNA. Researchers from China, Indonesia, England and the U.S. Researchers from China, Indonesia, England and the U.S. collected samples, genotyped the Y chromosomes and collected samples, genotyped the Y chromosomes and analyzed the results. They looked for specific mutations at analyzed the results. They looked for specific mutations at three locations on the Y chromosome and found that every three locations on the Y chromosome and found that every one of the 12,127 samples typed, carried one of these three one of the 12,127 samples typed, carried one of these three polymorphisms.polymorphisms.


These three markers can be used to test the completeness of These three markers can be used to test the completeness of the replacement of modern humans of African origin in East the replacement of modern humans of African origin in East Asia, because finding a male not carrying one of the three Asia, because finding a male not carrying one of the three polymorphisms would be indicative of a potential ancient polymorphisms would be indicative of a potential ancient origin and possibly leading to the rejection of complete origin and possibly leading to the rejection of complete replacement.replacement.This result indicates that modern humans of African origin This result indicates that modern humans of African origin completely replaced earlier populations in East Africa. completely replaced earlier populations in East Africa.

In linking the early dispersal of early In linking the early dispersal of early HomoHomo with its with its emergence, we are describing a hominid very different from emergence, we are describing a hominid very different from the australopithecines, whose bipedal but still ape-like the australopithecines, whose bipedal but still ape-like anatomy must have limited them to wooded locales. Thus the anatomy must have limited them to wooded locales. Thus the significance of an early dispersal to Asia is manifold. First, the significance of an early dispersal to Asia is manifold. First, the climatic conditions of cool aridity that played a great role in climatic conditions of cool aridity that played a great role in the emergence of the emergence of HomoHomo itself also drew hominid populations itself also drew hominid populations out of Africa and into Asia. Emergence and dispersal are, to a out of Africa and into Asia. Emergence and dispersal are, to a great extent, a product of environmental change. great extent, a product of environmental change.

Nevertheless, early Nevertheless, early HomoHomo emerged with a radical, yet still emerged with a radical, yet still generalized, set of characteristics that granted it ecological generalized, set of characteristics that granted it ecological hegemony across the subtropical Old World. An early hegemony across the subtropical Old World. An early intercontinental distribution signifies a hominid not adapted to intercontinental distribution signifies a hominid not adapted to specific territorial conditions, but adapted to manage many specific territorial conditions, but adapted to manage many local conditions through physical presence, technology and local conditions through physical presence, technology and flexible social organization. Ironically, as the first species to flexible social organization. Ironically, as the first species to use technology, early use technology, early HomoHomo colonized much of the subtropical colonized much of the subtropical Old World without the benefit of language, symbolic culture Old World without the benefit of language, symbolic culture or individual consciousness as we know it.or individual consciousness as we know it.

Critiques of the Critiques of the Replacement ModelReplacement Model

Critics of this genetic argument say that the rate of mutation is Critics of this genetic argument say that the rate of mutation is not necessarily constant and that there were flaws in the not necessarily constant and that there were flaws in the computer program that was used to construct the human computer program that was used to construct the human family trees; for instance, the results of the study varied with family trees; for instance, the results of the study varied with the order in which the data were entered. Further genetic the order in which the data were entered. Further genetic studies carried out since the mid 1990's have both supported studies carried out since the mid 1990's have both supported and undermined an African origin for modern humans. John and undermined an African origin for modern humans. John Relethford, of the State University of New York College at Relethford, of the State University of New York College at Oneonta, has pointed out that Africa could have had the Oneonta, has pointed out that Africa could have had the greatest diversity in mtDNA simply because there were more greatest diversity in mtDNA simply because there were more people living there during the last several hundred thousand people living there during the last several hundred thousand years. years.

Critiques of the Critiques of the Replacement ModelReplacement Model

Researchers from the University of Chicago and Yale Researchers from the University of Chicago and Yale University have discovered that variations in the DNA of the University have discovered that variations in the DNA of the Y chromosome and chromosome 12 have the greatest Y chromosome and chromosome 12 have the greatest diversity among Africans. This is consistent with the diversity among Africans. This is consistent with the replacement model. However, geneticists from Oxford replacement model. However, geneticists from Oxford University have found that the human betaglobin gene is University have found that the human betaglobin gene is widely distributed in Asia but not in Africa. Since this gene is widely distributed in Asia but not in Africa. Since this gene is thought to have originated more than 200,000 years ago, it thought to have originated more than 200,000 years ago, it undercuts the claim that an African population of undercuts the claim that an African population of Homo Homo sapiens sapienssapiens sapiens replaced East Asian archaic replaced East Asian archaic Homo sapiensHomo sapiens..

The Regional Continuity ModelThe Regional Continuity ModelFossil evidence is used to support the regional continuity Fossil evidence is used to support the regional continuity model. Its advocates claim that there has been a continuity of model. Its advocates claim that there has been a continuity of some anatomical traits from archaic some anatomical traits from archaic Homo sapiensHomo sapiens to modern to modern humans in Europe and Asia. In other words, the Asian and humans in Europe and Asia. In other words, the Asian and European physical characteristics have antiquity in these regions European physical characteristics have antiquity in these regions going back over 100,000 years. They point to the fact that many going back over 100,000 years. They point to the fact that many Europeans have relatively heavy brow ridges reminiscent of Europeans have relatively heavy brow ridges reminiscent of Neandertals. Similarly, it is claimed that Chinese facial Neandertals. Similarly, it is claimed that Chinese facial characteristics can be seen in Asian archaic characteristics can be seen in Asian archaic Homo sapiensHomo sapiens dating dating to 200,000 years ago. Like to 200,000 years ago. Like Homo erectusHomo erectus, East Asians today , East Asians today commonly have shovel-shaped incisors while Africans and commonly have shovel-shaped incisors while Africans and Europeans rarely do. This supports the contention of direct Europeans rarely do. This supports the contention of direct genetic links between Asian genetic links between Asian Homo erectusHomo erectus and modern Asians. and modern Asians.

The Regional Continuity ModelThe Regional Continuity ModelAlan Thorne of the Australian National University believes Alan Thorne of the Australian National University believes that Australian aborigines share key skeletal and dental traits that Australian aborigines share key skeletal and dental traits with people who inhabited Indonesia at least 100,000 years with people who inhabited Indonesia at least 100,000 years ago. The implication is that there was no replacement by ago. The implication is that there was no replacement by modern humans from Africa 60,000-50,000 years ago. modern humans from Africa 60,000-50,000 years ago. However, the evidence does not rule out gene flow from However, the evidence does not rule out gene flow from African populations to Europe and Asia at that time and African populations to Europe and Asia at that time and before. David Frayer of the University of Kansas believes before. David Frayer of the University of Kansas believes that a number of European fossils from the last 50,000 years that a number of European fossils from the last 50,000 years have characteristics that are the result of archaic and modern have characteristics that are the result of archaic and modern Homo sapiens Homo sapiens interbreeding.interbreeding.

The Regional Continuity ModelThe Regional Continuity ModelPart of the mitochondrial DNA was extracted recently from the Part of the mitochondrial DNA was extracted recently from the bones of a 60,000 year old modern bones of a 60,000 year old modern Homo sapiensHomo sapiens skeleton skeleton found in 1974 on the shores of Lake Mungo in Southeastern found in 1974 on the shores of Lake Mungo in Southeastern Australia. This is the oldest DNA that has been extracted from Australia. This is the oldest DNA that has been extracted from a human so far. Comparison of this DNA with that of nine a human so far. Comparison of this DNA with that of nine other ancient Australian skeletons, 2 Neanderthals, and 3,453 other ancient Australian skeletons, 2 Neanderthals, and 3,453 contemporary people from around the world indicates that contemporary people from around the world indicates that "Mungo Man" had a unique genetic marker. This indicates "Mungo Man" had a unique genetic marker. This indicates that a now lost genetic line of modern Homo sapiens existed in that a now lost genetic line of modern Homo sapiens existed in Australia prior to the arrival of later Australian Aborigines. Australia prior to the arrival of later Australian Aborigines. This evidence provides significant support for rejecting the This evidence provides significant support for rejecting the "out of Africa" complete replacement model of modern Homo "out of Africa" complete replacement model of modern Homo sapiens evolution.sapiens evolution.

The Regional Continuity ModelThe Regional Continuity ModelAlan Templeton, a geneticist at Washington University, has Alan Templeton, a geneticist at Washington University, has reported that a new computer based analysis of 10 different reported that a new computer based analysis of 10 different human DNA sequences indicate that there has been human DNA sequences indicate that there has been interbreeding between people living in Asia, Europe, and interbreeding between people living in Asia, Europe, and Africa for at least 600,000 years. These data suggest that the Africa for at least 600,000 years. These data suggest that the complete replacement model of complete replacement model of Homo sapiensHomo sapiens origin is origin is incorrect. According to Templeton, "humans expanded again incorrect. According to Templeton, "humans expanded again and again out of Africa, but these expansions resulted in and again out of Africa, but these expansions resulted in interbreeding, not replacement, and thereby strengthened the interbreeding, not replacement, and thereby strengthened the genetic ties between human populations throughout the genetic ties between human populations throughout the world." This view is gaining support among world." This view is gaining support among paleoanthropologists, but critics say that Templeton's sample paleoanthropologists, but critics say that Templeton's sample is still too small to be conclusive.is still too small to be conclusive.

Expansion Out of the Old World Expansion Out of the Old World


The world population of modern Homo sapiens began to grow rapidly after 50,000-40,000 years ago. It was around this time they expanded their territory by migrating into new regions. Their movement into northern areas coincided with the end of a long cold period that had begun about 75,000 years ago. By 60,000 years ago, modern humans apparently moved into Australia for the first time. Around 35,000-30,000 years ago, they moved into Northeastern Siberia.


Possibly as early as 30,000 years ago and certainly by 11,500 years ago, they migrated into North America via the Bering Land Bridge (or Beringia ). That intercontinental land connection appeared between Siberia and Alaska as a result of sea levels dropping more than 300 feet during the last ice age. Until that time, all human evolution had occurred in the Old World. The rate of human population growth has continued to accelerate until now. The current world population is over six billion and intercontinental migration and gene flow are at higher levels than ever before.


A tragic consequence of human migrations into new regions of the world has been the extinction of many animal species indigenous to those areas. By 11,000 years ago, human hunters in the New World apparently had wiped out 135 species of mammals, including 3/4 of the larger ones. Most of these extinctions apparently occurred within a few hundred years. It is likely that the changing climate at the end of the last ice age was also a contributing factor.

Expansion Out of the Old World Expansion Out of the Old World However, the same cannot be said for the animal extinctions that occurred following the arrival of aboriginal people in Australia and Polynesians in New Zealand. In both cases, humans were instrumental in wiping out easily hunted species. Vulnerable marsupials were the main victims in Australia. In New Zealand, it was mostly large flightless birds that were driven to extinction by hunters.

The Moa, a very large and apparently quite tasty flightless bird. It became extinct within centuries of the Polynesian arrival in New Zealand

Of course, the ultimate destruction of all giant flightless birds in New Zealand made this island nation safe for naked bungee jumping.

The Peopling of the New WorldThe Peopling of the New WorldEarly theories regarding the peopling of the New World were based on the concept of “Clovis First,” which stated that the first culture to enter the New World were big game hunters of the Clovis tradition, which first appears in the archaeological record in North America in the last part of the Pleistocene at around 11,600 years ago. Clovis hunters were thought to have crossed into North America from northeast Asia across a land bridge, which was a broad area of land up to a thousand miles wide that connected Siberia and Alaska. This land bridge, called Beringia, was exposed when sea levels were lower during the last glacial period of the Pleistocene and the shallow floor of the Bering sea was exposed.

The Peopling of the New WorldThe Peopling of the New WorldAccording to the this theory, groups of people that were culturally adaptated to the cold environments of northeast Asia would have followed the herds of the large mammals (like mammoth) that they relied on for the majority of their subsistence. As these herds moved across Beringia, groups of hunters and their families would have followed them into the New World. This was a slow process that could have taken generations to accomplish. The migration to the New World was not a conscious decision, but a natural consequence of subsistence.

Studies of pollen, fossil insects and peat from cores taken from the floor of the Bering Sea indicate that Beringia was covered with tundra similar to that found in the arctic areas of modern Alaska, and dates from peat indicate that at least parts of the bridge were above water as recently as 11,000 years ago.

Archaeologists excavating the remains of a mammoth bone hut in the Ukraine. Huts of this sort have been found in eastern Europe and Asia and predate the Clovis culture, but they are a good example of the sorts of cold environment adaptations that Clovis ancestors would have possessed.

The superstructure of bones would have been coveredwith mammoth hide.

The Peopling of the New WorldThe Peopling of the New WorldOnce across Beringia, the ancestors of the Clovis hunters could occupy an ice-free area in what is now Alaska. How did these people get down into the lower part of North America? Geological evidence suggests that as the glaciers began to recede at the end of the Pleistocene, an ice-free corridor opened up between the Laurentide ice sheet on the east and the Cordilleran ice sheet on the west. This corridor is supposedly how the Clovis people migrated south.

Map of Beringia showing the ice free area of Alaska and the migration route (in red) through the ice-free corridor between the Laurentide and Cordilleran ice sheets in North America. The exposed continental shelf is in light green.

The Peopling of the New WorldThe Peopling of the New WorldThe journey through the ice-free corridor was possible, though, only before 21,000 years ago and after 12,000 years ago. At about 21,000 to 19,000 years ago the Cordilleran Ice Sheet and Laurentide Ice Sheet coalesced thereby blocking the corridor and preventing passage. Although glacial ice retreated and the corridor re-opened about 18,000 years ago, the landscape was forbidding, a cold, semi-arid steppe with scant precipitation and only 10-25 percent of the land bearing sparse grass and sagebrush. Until about 12,000 years ago, such harsh climate, sparse vegetation, and minimal fauna probably would not have sustained human population.

The Peopling of the New WorldThe Peopling of the New WorldAn alternative to the ice-free corridor was first suggested by archaeologist Knut Fladmark. Fladmark hypothesized that travel would have been much more rapid by boat along the coast of the exposed continental shelf. Confirmation of this hypothesis is difficult, because the archaeological sites that would document the journey are now under 80 meters or more of water. However, there are other pieces of evidence that may support this model. For instance, the distribution of native American languages had their greatest clustering and distinctiveness along the West Coast, suggesting a longer period of time to diversify, compared to languages in the interior.

The Peopling of the New WorldThe Peopling of the New WorldThe coastal resources of northeastern Asia are very similar to those of northwest North America, and once people had adapted to hunting and gathering these resources, moving along that coastline would have been easy. It would not require much invention of new technologies or adaptation to drastically different climates, even in the course of a migration of thousands of kilometers.

The possibility that the colonizers used boats during their entry into the New World has also been proposed.

The Peopling of the New WorldThe Peopling of the New WorldIt would have been much easier and safer for sizable groups of migrating people, including children, pregnant women and the elderly, to move along the coast by boat. Also, the environment along the coast would have provided many more resources (i.e.. shellfish) that could have been gathered by all members of the group. By contrast, inland groups slogging across the tundra through the ice-free corridor would be dependent on the few adult, male big-game hunters in their band. During the best of times resources other than large game would not have been abundant.

The Peopling of the New WorldThe Peopling of the New WorldUsing boats would have aided greatly in the speed and safety of the coastal journey. Early use of boats has been demonstrated--boats would have been necessary for the colonization of Australia,which occurred 60,000 years ago, and there is also evidence of possible Homo erectus use of some sort of water craft to colonize islands that would not have been otherwise accessible. So it isn’t a stretch to suppose that the technology was available to the colonizers of the New World. Colonization by boat has another advantage as a mode of colonization. It does not require an ice-free corridor or a completely ice free continental shelf, and so could have occurred any time over the last 60,000 years.

Strong yet flexible skin boats that could carry more than 40 people is a technology found among the ancient, northern sea peoples of Europe, Asia and North America.

Eskimo skin boats

The Peopling of the New WorldThe Peopling of the New WorldIt has also been proposed, based on technological similarities in lithic technology that the origin of the Clovis culture is due to settlement in North America by people of the Upper Paleolithic Solutrean culture (21,000-16,500 B.P.) of southern France and the Iberian Peninsula. These first settlers were participating in a hypothesized “Paleo-Arctic Maritime Tradition,” whose economy was based on the hunting of large marine mammals and fishing from hide covered boats along the glacial ice margin in the north Atlantic.

A comparison of Solutrean and Clovis flaking techniques-the outre passé flake..

The Peopling of the New WorldThe Peopling of the New WorldSome of these sailors eventually worked their way over to the New World and settled in what is now the southeastern U.S., where the concentration of Clovis sites is greatest and where the oldest Clovis sites are located. Needless to say, there is contentious debate associated with this theory.

Other Evidence for the Other Evidence for the Colonization of the New WorldColonization of the New World

Dental MorphologyDental Morphology LinguisticsLinguistics Mitochondrial DNAMitochondrial DNA Other Genetic Data Other Genetic Data

Other EvidenceOther Evidence

Synthesis of linguistic, dental and genetic data suggest three migrations from Asia to America, with each wave leading to a separate linguistic group. Dental variation is greater in the north, and that there are three Native American dental (and parallel linguistic) clusters, Na-Dene, Aleut-Eskimo, and Amerind (Paleoamericans). The Aleut-Eskimo is the most recent, the Na-Dene (Athabaskan) the next oldest, and the Amerind the oldest.


There are limitations to mtDNA studies, such as the fact that molecular divergence can precede population divergence. When molecules in the mtDNA chain diverge, it only reflects when a population’s genetic composition diverges, but does not necessarily coincide with when a population became genetically isolated. Mutations evidenced today may predate divergence, and statistical change may be due more to population dynamics than temporal depth.


That said, most of the statistical measures based on models for mtDNA mutation rate assumptions suggest that the Amerindian colonization of the New World occurred between nineteen and seventy-eight thousand years ago. This by itself should suggest that the Clovis First theory for the peopling of the New World doesn’t hold water. But when the growing body of archaeological evidence indicating greater time depth of occupation is added to the mix, then debate of whether the New World was occupied during pre-Clovis times becomes moot.

Antiquity of New World Antiquity of New World Archaeological SitesArchaeological Sites

Pedra Furada, Brazil – 32,000 B.P.Pedra Furada, Brazil – 32,000 B.P. Meadowcroft Rockshelter, Pennsylvania – 16,200 B.P.Meadowcroft Rockshelter, Pennsylvania – 16,200 B.P. Topper, South Carolina 16,000+ B.P.Topper, South Carolina 16,000+ B.P. Cactus Hill, Virginia – 15,070 B.P.Cactus Hill, Virginia – 15,070 B.P. Monte Verde, Chile 14,500 B.P.Monte Verde, Chile 14,500 B.P.

Monte Verde projectile points and a wood foreshaft

Human footprint from the 14,500 B.P. level at the Monte Verde site

Until 1997 no site was widely accepted as pre-dating the Clovis culture (11,000 to 11,500 radiocarbon years before present). That year, a blue-ribbon commission of Paleoindian specialists visited Monte Verde, a site in Chile with dates averaging 12,500, and declared it to be valid. Other possible pre-Clovis sites include Hebior and Schaefer, Cactus Hill, and Topper. Meadowcroft and Pedra Furada have also been proposed as pre-Clovis. Additional early sites include Taima-Taima, Pedra Pintada, Santa Barbara in the Channel Islands, Quebrada Tacahuay, and Quebrada Jaguay. (Map by Joe LeMonnier).

Other EvidenceOther EvidenceBy various measurements of genetic distance, New World populations have more similarities to east Asian populations that they do to other populations around the world (no real surprise). However, there are some intriguing differences between the populations. Native Siberians lack one peculiar mtDNA mutation that appeared in the Amerinds 6,000 to 10,000 years ago. This particular mutation pattern is also found in aboriginal populations in Southeast Asia and in the islands of Melanesia and Polynesia. This suggests contact between these populations, but how? The route by which this gene found its way into the population is unknown. It either came across the Pacific to Central and South America or up the east coast of Asia and across the northern Pacific to Alaska and Canada.

Other EvidenceOther EvidenceThere are also genetic similarities between New World populations and the indigenous Ainu of Japan, which exhibit more genetic similarities to European populations than to other Japanese or mainland Asian populations (shades of Kenniwick Man). These similarities have been interpreted variously as either representing a common origin for these two populations (more likely) or a Jomon fishing boat that was blown off course (not so much).

There are even some investigators that have suggested contact with Africa, based on the cranial morphology of a skeletal population from an archaeological site in Brazil (!).

Other EvidenceOther EvidenceThe one thing that should become obvious from the above discussion, is that deducing the timing and nature of migration and diffusion is never a clean cut process. The theories about the origin of Homo sapiens and the subsequent radiation of the species is still a topic that is debated, and as the above evidence demonstrates, it is unlikely that any long-term migration is the product of a unilinear process. Several different groups have colonized the The New World over time and contributed their genes to the populations that lived here, and it is just as likely that many other groups arrived over time and perished without contributing to the genetic makeup of the population.

Hypothesized prehistoric migration routes into the New World, including the ice-free corridor, the coastal route, the Solutrean entry, and the Polynesian and Australian mariners.

We’ve looked at human We’ve looked at human migration at a global scale, let’s migration at a global scale, let’s

examine a case of human examine a case of human migration on a smaller scale.migration on a smaller scale.

So, What Happened Once People So, What Happened Once People Arrived in the New World?Arrived in the New World?

Well, they didn’t just spread out, Well, they didn’t just spread out, settle down and stay put for the next settle down and stay put for the next

15,000 years, THAT’S for sure. 15,000 years, THAT’S for sure.

A Late Prehistoric Example of A Late Prehistoric Example of Migration in North America:Migration in North America:

The Numic Expansion The Numic Expansion

Which offers problems no less complex or less hotly debated than those cited for the migration scenarios discussed above.

The Numic Expansion The Numic Expansion The Numa are several groups of people that speak related languages of the Uto-Aztecan Family, which arrived in the southern Sierra Nevada-Mohave Desert area from northern Mexico approximately 5000 years ago. This area (southwestern or central Great Basin) is considered to be the ancestral Numic homeland. It is from here that the Numic groups expanded north and east into the Rocky Mountains, Basin and Range and Northern Plains regions. The Great Basin

The Numic Expansion The Numic Expansion

The Numa can be divided into three groups based on language: the western group consisting of the Mono and Northern Paiute, the Central group that contains the Panamint, Western, Northern and Eastern Shoshone, and the Southern group, which consists of the Kawaiisu, Chemehuevi, Southern Paiute and Ute.

The environment of the Numa homeland is particularly arid and harsh, and traditional economies have always been based on highly mobile hunting and gathering.

Traditional Paiute and Shoshone lifeways in the Great Basin.

The modern distribution of Numic-speaking peoples in western North America

There has been considerable debate in the archaeological community concerning the place of origin and timing of the migration of the Numa throughout the West. Most archaeologists (but not all) agree that the likely Numa homeland was in either the southwestern or central Great Basin. There are also several schools of thought regarding the timing of the expansion out of this homeland. These can be roughly divided into the early and late schools.

There is less agreement on why the expansion occurred and who the people were that the Numa replaced as they expanded.

Some archaeologists believe that the expansion out of the Numic homeland occurred soon after the arrival of the Uto-Aztecans from Mexico. This would have occurred just after a mid-Holocene climatic arid episode formerly known as the Altithermal.

Numic speakers would have come into contact with other hunter-gatherer groups, and it is unknown if they replaced these peoples or intermixed with them. Regardless, in this scenario the Middle and Late Archaic populations throughout the Intermountain West would have been Numic in makeup.

Other archaeologists believe that the expansion occurred much later, at around 1000 B.P. This would have been well into the Late Prehistoric period, and it would have brought the Numa into contact with sedentary Horticultural cultures.

This later expansion has some support from archaeological data, especially in the documentation of the entry of the Ute and southern Paiute in the southern area. This later expansion makes sense for several reasons.

The big question is, how did the Numa expand relatively The big question is, how did the Numa expand relatively rapidly into an area that was already inhabited? There are rapidly into an area that was already inhabited? There are theories that invoke an adaptation that was more efficient than theories that invoke an adaptation that was more efficient than that possessed by the native populations that were replaced, but that possessed by the native populations that were replaced, but they do not address the problem of differences in population they do not address the problem of differences in population density. As was pointed out above, the Mohave Desert and the density. As was pointed out above, the Mohave Desert and the Great Basin as a whole are harsh environments, and historically Great Basin as a whole are harsh environments, and historically supported native population densities lower than anywhere in supported native population densities lower than anywhere in North America other than the Arctic. North America other than the Arctic.

How could a relatively small population with low density push How could a relatively small population with low density push into areas with larger, denser populations? into areas with larger, denser populations?

Data suggest that there were significant and precipitous Data suggest that there were significant and precipitous decreases in population throughout western North America decreases in population throughout western North America starting approximately A.D. 850 and continuing through the starting approximately A.D. 850 and continuing through the Anasazi abandonment of the Four Corners region in the late Anasazi abandonment of the Four Corners region in the late 1313thth century. This depopulation may have been associated century. This depopulation may have been associated with climatic deterioration and increased frequency of drought with climatic deterioration and increased frequency of drought prior to A.D. 1200, and elsewhere has been correlated with the prior to A.D. 1200, and elsewhere has been correlated with the Medieval Climatic Anomaly. Depopulation would have set the Medieval Climatic Anomaly. Depopulation would have set the scene for a rapid radiation of a relatively small group of people scene for a rapid radiation of a relatively small group of people that were pre-adapted to harsh environments. that were pre-adapted to harsh environments.

Now that we have examined the nature of population dynamics Now that we have examined the nature of population dynamics on very large and moderately large scales, let’s examine the on very large and moderately large scales, let’s examine the nature of population dynamics on a smaller regional scale.nature of population dynamics on a smaller regional scale.

Population Dynamics of Population Dynamics of Prehistoric Hunter–Gatherer Groups in Prehistoric Hunter–Gatherer Groups in

Eastern ColoradoEastern Colorado

Recognition of a Regional Pattern:Recognition of a Regional Pattern:Peaks in Late Prehistoric Radiocarbon Peaks in Late Prehistoric Radiocarbon

Age FrequencyAge Frequency

Platte River Basin (1300-1200 BP).Platte River Basin (1300-1200 BP). Arkansas River Basin (1100-1000 BP).Arkansas River Basin (1100-1000 BP). Northern Colorado River Basin ( 1300-1200 BP).Northern Colorado River Basin ( 1300-1200 BP). Wyoming (1200-1000 BP).Wyoming (1200-1000 BP).

From Gilmore et. al. (1999)

Platte Basin Radiocarbon Ages

Adapted from Gilmore et. al. (1999)

Adapted from Zier and Kalasz 1999

Arkansas Basin Radiocarbon Ages

From Reed and Metcalf (1999)

Northern Colorado River Basin

From Frison (1993)

Wyoming

Platte BasinCurve Peaks1300-1200 B.P.

Platte BasinCurve Peaks1300-1200 B.P.

Arkansas BasinCurve Peaks 1100-1000 B.P.

Arkansas BasinCurve Peaks 1100-1000 B.P.

The Data SetThe Data Set

Distribution of archaeologicalsites and isolatedfinds in the Platte and Arkansas River Basins (N=17,812)

Distribution of siteswith radiocarbon ages between3000 and 100 BP

Distribution of archaeological siteswith associated radiocarbon ages3000-100 BP

C-14 ages n=621Components n=534

If changes in the number of radiocarbon dates If changes in the number of radiocarbon dates are accepted as representing changes in relative are accepted as representing changes in relative population, then it is also reasonable to assume population, then it is also reasonable to assume that changes in the spatial distribution of these that changes in the spatial distribution of these dated occupations represents changes in the dated occupations represents changes in the spatial distribution of population. spatial distribution of population.

Middle Archaic (5000-3000 BP)

Late Archaic (3000-1850 BP)

Early Ceramic (1850-800 BP)

Middle Ceramic( 800-400 BP)

All Middle Ceramic Cultures

Apishapa Phase (900-500 BP)

Geographic Mean Centers for Archaeological Sites by Cultural Period

Geographic Mean Centers for Archaeological Sites by Cultural Period

This shows the progress south and east of the geographic mean centers of sites assigned to cultural periods by temporally diagnostic artifacts.

This shows the progress south and east of the geographic mean centers of sites assigned to cultural periods by temporally diagnostic artifacts.

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Significance?Significance?

Difference of means tests comparing the locations Difference of means tests comparing the locations (UTM northings and eastings) of the set of all stable (UTM northings and eastings) of the set of all stable sites (2400-1200 BP) to the locations of the set of all sites (2400-1200 BP) to the locations of the set of all

sites falling within the hypothesized period of sites falling within the hypothesized period of population movement south (1200-500 BP) population movement south (1200-500 BP)

are significant atare significant at p=.05p=.05

Significance?Significance?

Not only is the movement south significant, but the Not only is the movement south significant, but the movement from west to east is also significant. movement from west to east is also significant.

What does this mean?What does this mean?

Are we looking at Are we looking at Population Movement, or Population Movement, or

Differential Rates of Natural Differential Rates of Natural Increase?Increase?

Probably Some of BothProbably Some of Both

As the climate gradually became warmer and As the climate gradually became warmer and wetter between A.D. 1 and 900, two things wetter between A.D. 1 and 900, two things apparently happened. The Plains became more apparently happened. The Plains became more productive; plants were more abundant and more productive; plants were more abundant and more productive, and so animals were also more productive, and so animals were also more abundant. People spent more of their time at abundant. People spent more of their time at lower elevations, because the resources that the lower elevations, because the resources that the mountains could provide were not as critical as mountains could provide were not as critical as they had been. And human population increased. they had been. And human population increased.

As you can see from the following radiocarbon frequency curves, population apparently began to decrease first in the mountains between about 1600 to 1300 BP (top), followed by the Foothills at 1300 (middle), and then finally on the Plains at 850 BP. Based on the slope of the respective curves, the drop in population was more gradual in the mountains (900 years), more rapid in the Foothills (500 years), and precipitous on the Plains (300 years). This may indicate a relatively rapid out migration from the Plains, where the more gradual drops in the mountains and Foothills suggests a decrease in the frequency and duration of visits.

After about A.D. 900, population begins to drop After about A.D. 900, population begins to drop precipitously, perhaps in response to a return to precipitously, perhaps in response to a return to more arid conditions. Instead of returning to a more arid conditions. Instead of returning to a pattern where the resources in the mountains pattern where the resources in the mountains became more important relative to decreasing became more important relative to decreasing resources on the Plains, population also decreases resources on the Plains, population also decreases in the mountains. This is a pattern that is in the mountains. This is a pattern that is apparently reflected across much of the west. apparently reflected across much of the west.

One possible explanation is that this dry period One possible explanation is that this dry period was not hot and dry, but cold and dry. This might was not hot and dry, but cold and dry. This might explain why both the plains and the mountains explain why both the plains and the mountains were apparently abandoned at the same time. It were apparently abandoned at the same time. It was too dry on the Plains, which which resulted was too dry on the Plains, which which resulted in decreased resource availability, and in the in decreased resource availability, and in the mountains it was too cold, which also resulted in mountains it was too cold, which also resulted in decreased resources.decreased resources.

There wasn’t anywhere to go that was productive There wasn’t anywhere to go that was productive enough to support the population that had enough to support the population that had increased in size and density over the past 900 increased in size and density over the past 900 years. years.

A measure of the relative mobility of prehistoric A measure of the relative mobility of prehistoric people called the the people called the the Component Complexity Component Complexity IndexIndex (CCI) can help to determine if there was (CCI) can help to determine if there was movement from the Platte basin to the Arkansas movement from the Platte basin to the Arkansas basin as a response to climate change. basin as a response to climate change.

A higher aggregate CCI for all the sites in a region A higher aggregate CCI for all the sites in a region during a particular century suggests a combination during a particular century suggests a combination of longer occupations, and/or increased frequency of of longer occupations, and/or increased frequency of visits and/or more people occupying sites during visits and/or more people occupying sites during occupations dated to that century.occupations dated to that century.

In contrast, a lower aggregate Component Complexity Index for a In contrast, a lower aggregate Component Complexity Index for a region during a particular time is indicative of greater residential region during a particular time is indicative of greater residential mobility and possibly smaller populations and/or lower population mobility and possibly smaller populations and/or lower population densities.densities.

Component Complexity Index

Although the peaks in the component curves Although the peaks in the component curves are offset by 200 years between the Platte and are offset by 200 years between the Platte and Arkansas basins, the Component Complexity Arkansas basins, the Component Complexity Index curves are concordant, suggesting that Index curves are concordant, suggesting that even though population was fluctuating, the even though population was fluctuating, the relative mobility of the populations in both relative mobility of the populations in both places was following the same trends at the places was following the same trends at the same time.same time.

There is a trough in both CCI curves between There is a trough in both CCI curves between 1250 and 950 BP, which corresponds to the 1250 and 950 BP, which corresponds to the period between the peak in radiocarbon period between the peak in radiocarbon frequency in the Platte basin at 1300-1200 BP frequency in the Platte basin at 1300-1200 BP and the peak in the Arkansas at 1100-1000 BP. and the peak in the Arkansas at 1100-1000 BP. This indication of greater mobility in both This indication of greater mobility in both basins during a period of decreasing basins during a period of decreasing population in the Platte and increasing population in the Platte and increasing population in the Arkansas could represent population in the Arkansas could represent migration from north to south. migration from north to south.

The peaks and subsequent decreases in The peaks and subsequent decreases in radiocarbon age frequency occur hundreds of radiocarbon age frequency occur hundreds of years prior to the onset of the Pacific climatic years prior to the onset of the Pacific climatic episode (850-400 BP), which is thought to have episode (850-400 BP), which is thought to have contributed to dry conditions in eastern Colorado. contributed to dry conditions in eastern Colorado. The Pacific episode would have been a likely The Pacific episode would have been a likely culprit for contributing to population movement culprit for contributing to population movement and decline.and decline.

In fact, the peaks and subsequent decline in both In fact, the peaks and subsequent decline in both basins occurs in the middle of the Neo-Atlantic basins occurs in the middle of the Neo-Atlantic episode (1260-850), which is hypothesized to have episode (1260-850), which is hypothesized to have been a period of greater summer precipitation and been a period of greater summer precipitation and higher carrying capacity.higher carrying capacity.

Component Frequency Curves and Paleoclimatic Episodes

The drop in population in both the Platte and The drop in population in both the Platte and Arkansas basins does, however, correspond to Arkansas basins does, however, correspond to the onset of the Medieval Climate Anomaly the onset of the Medieval Climate Anomaly (remember?) mentioned above. The decrease (remember?) mentioned above. The decrease in population in eastern Colorado also in population in eastern Colorado also correlates to the drop in populations throughout correlates to the drop in populations throughout the region and west into the Colorado Plateau, the region and west into the Colorado Plateau, the Great Basin and California. the Great Basin and California.

Introduction of new technologies such as the Introduction of new technologies such as the bow and arrow and ceramics to the prehistoric bow and arrow and ceramics to the prehistoric inhabitants of eastern Colorado in the first few inhabitants of eastern Colorado in the first few centuries A.D. may have enhanced already centuries A.D. may have enhanced already established trends in prehistoric population established trends in prehistoric population growth by contributing to the more efficient growth by contributing to the more efficient exploitation of food resources. exploitation of food resources.

The onset of dryer conditions associated with The onset of dryer conditions associated with the Pacific paleoclimatic episode that occurred the Pacific paleoclimatic episode that occurred after 850 BP almost certainly contributed to after 850 BP almost certainly contributed to already established trends of population already established trends of population decrease. The introduction of epidemic disease decrease. The introduction of epidemic disease by Europeans some five to seven hundred years by Europeans some five to seven hundred years after population begins to decrease also after population begins to decrease also undoubtedly contributed significantly to further undoubtedly contributed significantly to further decline in population. decline in population.

Changes in subsistence, technology, economy Changes in subsistence, technology, economy and climate all contributed to prehistoric and climate all contributed to prehistoric population dynamics during the past 3000 population dynamics during the past 3000 years…years…

But…But…

The mechanisms providing the initial impetus that The mechanisms providing the initial impetus that resulted in almost exponential growth in proxy resulted in almost exponential growth in proxy population starting at around 2200 BP and the population starting at around 2200 BP and the equally precipitous decrease in population that equally precipitous decrease in population that occurred after about 1200-1000 BP in eastern occurred after about 1200-1000 BP in eastern Colorado still remain a mystery.Colorado still remain a mystery.

ConclusionsConclusions

If the radiocarbon age and component If the radiocarbon age and component frequency curves are accepted as a frequency curves are accepted as a proxy for general population trends, proxy for general population trends, and the spatial distributions of and the spatial distributions of radiocarbon ages represent the spatial radiocarbon ages represent the spatial distributions of prehistoric people, distributions of prehistoric people, what are the implications? what are the implications?

There is a dramatic There is a dramatic increaseincrease in population in population in the region and beyond starting at in the region and beyond starting at approximately 2200 BP and peaking at approximately 2200 BP and peaking at approximately 1200-1000 BP.approximately 1200-1000 BP.

There is an equally dramatic There is an equally dramatic decreasedecrease in in population in the region that begins at population in the region that begins at approximately 1000 BP, or 500 years approximately 1000 BP, or 500 years prior to European contact and the prior to European contact and the introduction of epidemic European introduction of epidemic European diseases.diseases.

There is evidence that prehistoric There is evidence that prehistoric population change in eastern Colorado can population change in eastern Colorado can be partially explained by migration. be partially explained by migration.

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The Numic Expansion:

Jones, Terry L., Gary M. Brown, L. Mark Raab, Janet L. McVicar, W. Geoffrey Spaulding, Douglas J. Kennett, Andrew York, and Phillip L. Walker (1999) Environmental Imperatives Reconsidered. Current Anthropology 40(2):137

Madsen, David B. and David Rhode, eds. (1994) Across the West: Human Popuilation Movement and the Expansion of the Numa. University of Utah Press, Salt Lake City.

Shennen, Stephen (2000) Population, Culture History, and the Dynamics of Culture Change. Current Anthropology 41(5):811.

The Numic Expansion:

Jones, Terry L., Gary M. Brown, L. Mark Raab, Janet L. McVicar, W. Geoffrey Spaulding, Douglas J. Kennett, Andrew York, and Phillip L. Walker (1999) Environmental Imperatives Reconsidered. Current Anthropology 40(2):137

Madsen, David B. and David Rhode, eds. (1994) Across the West: Human Popuilation Movement and the Expansion of the Numa. University of Utah Press, Salt Lake City.

Shennen, Stephen (2000) Population, Culture History, and the Dynamics of Culture Change. Current Anthropology 41(5):811.

out of africa (or not) the incredibly complex and mostly true story of the origin and dispersal of...

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