Essays Out Of Africa Hypothesis

Analysis of Two Competing Theories on the Origin of Homo sapiens sapiens: Multiregional Theory vs. the Out of Africa 2 Model

There are many competing theories regarding the origins of Homo sapiens sapiens. The multi-regional hypothesis and the Out of Africa 2 model are two such competing theories that are most controversial among those who are concerned with how anatomically modern humans evolved to out-compete all other hominids. This essay seeks to analyse these two highly contentious theories in order for the reader to gain insight into this debate and to make an informed decision as to which theory seems most comprehensible.  The conclusion made at the end of this paper shows how, through molecular evolutionary theories, fossil records and palaeoanthropology, the Out of Africa 2 model provides a more convincing argument to such a debate regarding the origins of Homo sapiens sapiens.

 

The most intriguing and perplexing question human kind has asked begins with ‘where have we come from?’ This subsequently highlights numerous other questions in need of answering before a concrete conclusion can be made; ‘who did we evolve from and what in our evolution led us to out-compete all other hominid species?’

Naturally, many theories have been postulated in an attempt to answer such questions, two of which stand out predominately – the multi-regional model and the Out of Africa 2 model. Each hypothesis demonstrates a different origin of Homo sapiens sapiens deduced from evidence found in fossil records, DNA sequences and archaeological sites. In examining the evidence of these theories, it should become clear which hypothesis is the lead contender in explaining where modern humans originated.

The Multi-regional Hypothesis

The multi-regional hypothesis argues that our early hominid ancestors, including Homo ergaster and Homo heidelbergensis, migrated out of Africa and thus the evolution of modern humans took place in different parts of the world – a process termed regional continuity (Pettitt, P 2009a: 125-173) . This theory places great emphasis on the notion of steady evolutionary alterations or changes that happen in different regions and produce diverse variations of the species. Evolution of this kind is kept at a regular rate due to an amalgamation of cultural progress and ‘gene flow’ or interbreeding, thus keeping all lineages evolving at the same time (EP 2006a:70). This process is characterized as parallel evolution, which suggests a subtle morphological resemblance between populations of species who are geographically separated (EBO 2011).

This idea was first postulated in 1940 by Franz Weidenreich (1873-1948), who noticed considerable similarities between the archaic Peking man fossils and modern humans from China. However, Weidenreich did not refer to his evolutionary hypothesis as the ‘multi-regional model’ -  instead, he used the term ‘Polycentric’ (Wikipedia 2011).

Milford Wolpoff, American Paleoanthropologist and advocate of the multi-regional hypothesis, developed Weidenriech’s theory along with Alan Thorne, allegorically suggesting that gene flow can be likened to that of individuals swimming in a pool – although they maintain their individuality, they are often influenced by the spreading ripples made by the activity of other people in the water. This, they suggest, is the ‘equivalent of genes flowing between populations’ (Wolpoff, M and Thorne, A 1992).

This theory is now highly discredited by many scholars due to the lack of supporting evidence. It was once thought that the fossil records from Australia and Asia could be understood as showing evidence for such regional continuity. The facial structure of the Dali cranium from China, for example, appears to be modern in its proportions. The cheek bones are highly delicate. For a proponent of the multi-regionalist theory, this indicates an intermediate stage between earlier archaic hominids (i.e. Homo erectus found at sites such as Lantian, China) and later Holocene populations living after 10,000 BC. However, the conditions of these fossil materials were poorly preserved and, in the case of the Dali cranium, highly mutilated through post-depositional weight loading. There are also no fossil materials dating from between 100,000 and 30,000 BC – this gap undermines the multi-regional hypothesis as it indicates a lack of any modern Chinese anatomical features from before 100,000 years ago (Pettitt, P 2009b:130).

The strong anatomical basis of the multi-regional hypothesis is a weakness of the theory. Chris Stringer highlights this, suggesting that the physical features used to support the regional continuity (i.e. flatness of the frontal bone and the constriction of the skull behind the orbital area) are not only found in specific regions such as Asia, but all around the world. This suggests that these physical features are in fact general Homo characteristics and cannot therefore be used in support of the multi-regionalist view (Stringer, C 1984, cited by Pettitt, P 2009:131).

The most highly damaging critique of this hypothesis stems from recent genetic research. The multi-regional model proposes a shared genetic lineage between archaic Neanderthals and modern humans. Geneticists have proved this idea to be purely imaginative. Work on the Neander Valley skeleton and others have demonstrated that such a link in descent does not exist.  It has been widely credited that Neanderthals did not contribute, in any case, to the human genome and therefore the evolution of modern humans (EP 2006b:71).

On the basis that there is little supporting evidence to suggest the validity of the multi-regionalist view, it would seem that its competitor, the Out of Africa 2 model or population replacement model, has the upper hand. The Out of Africa 2 model is a strong contender in accounting for the spread and development of anatomically modern Homo sapiens sapiens (EP 2006c: 69).

The Out of Africa 2 Model

It is widely recognized among both archaeological and anthropological academics that archaic Homo populations did leave Africa in an initial phase of globalisation, called the Out of Africa 1 model. Following this, the population replacement hypothesis maintains that modern humans evolved in Africa from the ancestral hominids that did not travel out of this continent in the first stage of global colonisation. It is then argued in this model that once evolved as anatomically modern humans, Homo sapiens sapiens travelled out of Africa to explore, colonise and rapidly replace the archaic Homo population. This movement suggests a second wave of hominid species emerging from Africa, thus the title: the Out of Africa 2 model (EP 2006d: 69).

There are numerous assumptions that are endorsed by the Out of Africa 2 model, the first of which predicts that the earliest fossils of Homo sapiens sapiens will only be found in Africa along with any transitional fossils, marking the evolutionary process of these modern humans. Such fossils will not be found outside this area. Secondly, this model suggests that modern-day human populations may not necessarily share lineages or links with the earlier populations that inhabited the same region. This idea stems from the notion that the new populations of modern humans that inhabit an area will replace any archaic Homo species that occupy this region, thus establishing a new lineage of descent (Pettitt, P 2009c:128-129). Evidence in support of these ideas exists through multiple sources, showing the clear superiority of this theory in contrast with the multi-regionalist model.

Such evidence can be found in the striking research of molecular geneticists; research which supports the idea of modern humans arising in one place and subsequently spreading elsewhere.

Molecular Evolutionary Theories

The DNA studied as reflected in Rebecca Cann and Allan Wilson’s research resides in mitochondria (mtDNA­). This cellular organelle converts food into energy that the entire cell can then use. It is also passed on only through females thus preserving a family record, altered singularly through mutations. Cann and Wilson believe that mtDNA mutates at a steady rate so that molecular geneticists can calculate dates of movement (Renfrew, C and Bahn, P 2008: 464). This process evolved from the works of Vincent Sarich who, by calculating the mutation rate of different species that could be reliably dated by fossils, managed to create a way of calibrating the ‘molecular clock’ (Cann, R and Wilson, A. 1992a: 68).

Through genetic comparisons of dates of mutations, Rebecca Cann and Allan Wilson have reason to believe that all maternal lineages can be traced back to one individual woman who came from one region (most likely Africa) and lived 200,000 years ago – this female individual has been nicknamed ‘mitochondrial Eve’.  In their paper, The Recent African Genesis of Humans (1992), Cann and Wilson stress that ‘Eve’, whilst not being the only woman to procreate, is definitely a woman whose lineage survived throughout the ages. This paper highlights that other maternal lineages apart from ‘Eve’s’ must have died out because these women where giving birth to males instead of females and thus, mtDNA could not be passed on to offspring (Cann, R and Wilson, A.  1992b).

In the same line of research, a theoretical most common recent ancestor (MCRA) has been found to be a male, also living in Africa, from as early as 142,000 BC. This individual is thought to be the man from whom all modern people are descended, tracing back only from paternal lines of a family tree – he has been nicknamed ‘Y-chromosomal Adam’. Y-chromosomes can only be passed on paternally, from father to son. Like the study of mtDNA, mutations of Y-chromosomes can also be calibrated and dated to reveal a reconstruction of ancestral Y-chromosomal DNA sequences (Cruciani, F 2011, cited by Wikipedia 2011).

Through applying molecular evolutionary theories such as that of ‘mitochondrial Eve’ and ‘Y-chromosomal Adam’, the Out of Africa 2 model is strengthened as a hypothesis. The research of Sarich, Cann and Wilson provide firm evidence to suggest that modern humans descended from archaic Homo populations living in Africa. This can be shown in the lineages of descent and the mutations that had occurred genetically from 200,000 years ago to the present modern day. Moreover, the diversity seen in mitochondrial DNA in African populations is unparalleled in its diversity. This is powerful evidence in support of the Out of Africa 2 model as it supports the theory that there are lineages in Africa tracing back more than 100,000 years (Anderson-Mann, S 2005/2006).

The Out of Africa 2 model seems convincing as a hypothesis for the origins of Homo sapiens sapiens, not just because it is strongly supported by evidence in genetics, but because of the research involved in palaeoanthropology.  Fossil hominid evidence is crucial in determining how and from whom a species might have evolved. The multi-regional model, whose fossil records rested on the finds of evolutionary physical features of archaic hominids in Australia and Asia, seems weak in comparison with the fossil evidence supporting the Out of Africa 2 model.

The Anatomy of Homo sapiens sapiens and the use of Fossil Records

Homo sapiens sapiens must clearly be defined anatomically. This is critical because it allows for the recognition of modern humans in the fossil record. Also, features of modern humans may be found in some hominid fossils that we know not to be Homo sapiens sapiens, suggesting a transitional being or a different Homo species entirely (Pettitt, P 2009d: 130).

For this reason, the characteristics of the cranial features of anatomically modern humans have been defined precisely. The cranial capacity of Homo sapiens sapiens is found usually to be in excess of 1350 cc, although this can vary. The frontal bone or forehead is relatively vertical in comparison with other hominids. Homo habilis, for example, carries a frontal bone that slopes backwards quite sharply. The cranial vault of the anatomically modern human is described by Paul Pettitt as high with paralleled walls. Homo sapiens sapiens can be characterized by their rounded occipital region (back of the head) which lacks a prominent horizontal bulge called the occipital torus; a vast contrast with the protuberant occipital torus of Homo neanderthalensis (Pettitt, P 2009e: 132).

Recognising these characteristics of the modern human are essential to answering the question of where the modern human originated. Excavations at various sites in Africa have unearthed many hominid fossils, in particular, skulls.  Such finds have been used to identify transitional specimens who display primitive yet modern cranial features. This evidence suggests that modern humans were evolving in Africa from as early as 250,000 years ago (Pettit, P 2009f: 132)

In 1976, a cranium was recovered from deposits in Bodo, Africa, which also contained Acheulean tools. These tools were studied using the argon-argon method which dated the finds to between 670,000 and 600,000 years ago. This is consistent with some of the Bodo cranium’s features as it possesses numerous characteristics of Homo ergaster i.e. a robust facial skeleton, thick bones and a forehead that bulges from the centre.  However, this specimen bears an overall resemblance to crania dated to after 300,000 BC which is shown in the endocranial capacity, estimated at close to 1300 cc. Homo ergaster supported a cranial capacity of 900 cc, on average. Therefore, the Bodo cranium suggests that encephalization (gradual enlargement of the brain) was occurring among archaic Homo species in Africa around 600,000 years ago. This supports the theory of evolutionary change, specific to regions in Africa, of Homo populations (Pettitt, P 2009g: 133).

Transitional fossils found in Herto, Ethiopia, also offer significant support for the Out of Africa 2 model. Two adult and one child crania were discovered in deposits that, through argon-argon methods, were dated to 160,000 and 154,000 BC (late/middle/ early Upper Pleistocene era). The crania, like the Bodo cranium, sustain clear features characteristic of Homo ergaster but also bear modern human features (Pettit, P 2009h: 135). Scientists have classified this species as Homo sapiens idaltu, in order to emphasize their transitional nature presumably between Homo rhodesiensis to anatomically modern Homo sapiens (Foley, J 2003).

By the early Upper Pleistocene era (125,000 – 70,000 BC), fossils relating to Homo populations appear modern and are regarded as such. The African fossil record is littered with fragments of what are presumed to be anatomically modern human crania. Equus Cave in South Africa revealed a fragmentary mandible whose proportions and morphology of teeth relate closely to those of modern humans. Similarly, a jaw was discovered from the Cave of Hearths at Makapansgat in South Africa that bears subtle hints of a chin not unlike that of Homo sapiens sapiens (Stringer and Gamble 1993, cited by Pettitt, P 2009: 137).

Behavioural Patterns of Anatomically Modern Homo sapiens sapiens

The archaeology of Africa dating from the Middle Stone Age (100,000 years ago) strongly suggests an emergence of new behavioural patterns that differ greatly from those of archaic hominids. These new behavioural traits are seen to be modern in form. They develop at the same time as the biological emergence of anatomically modern Homo sapiens so it is suggestive of a leap in cognitive and intellectual evolution. Such behavioural modifications include clear organization of space, shown in dwelling structures; high frequencies in transport over long distances, of lithic raw materials; symbolic and non-figurative art; jewellery being made from shells and the growth in population density (Thames and Hudson 2008).

A shift in diet is also evidence of behavioural modernity as it suggests the growth of a broader-spectrum in economy.  Seafood is rich in the diet of behaviourally modern Homo sapiens sapiens. Fresh water fish and brackish or salt water fish remains have been found at many sites in Africa including White Paintings Shelter in Botswana and shell middens at Klasies River. At the site of Bombos Cave in South Africa, three Middle Stone Age phases were excavated providing more evidence in the evolution of behavioural patterns. Subsistence strategies found in all three phases were extensive and far-reaching; marine mammals, shellfish, fish and reptiles were all consumed at this site. The use of fire is also evident at Bombos Cave as Wood ash is scattered throughout all three phases, indicative of hearths. This shows that sites on which modern humans lived were becoming modified to sustain living (Pettit, P 2009h: 142).

The overlap in chronologies between archaeological evidence of behaviour and the fossil record of modern humans supports the Out of Africa 2 model, strengthening the view that Homo sapiens sapiens where evolving, anatomically and intellectually, in Africa.

Conclusion

On balance it seems that the Out of Africa 2 model holds more weight as a hypothesis as opposed to the multi-regional model. The multi-regional model simply lacks substantial evidence. The fossil records used to support this theory are weak and do not provide any significant evidence to suggest that Homo sapiens sapiens evolved outside of Africa.

Agreement for the Out of Africa 2 model seems highly logical in answering the question of where modern humans originated. This is because of the vast amounts of evidence that can be used in support of the theory. The molecular genetic research of Sarich, Cann and Wilson provide a firm basis in explaining that our direct ancestral lineage begins in Africa. The African fossil records also shows that modern humans where evolving in Africa. This can be seen from transitional fossils like the Homo sapiens idaltu cranium. Also, archaeological evidence explains how behavioural patterns evolved, as well as modern human morphology, in order to sustain a way of living suited to this advanced intellectual being. Subsistence strategies progressed and expanded along with more complex dwellings, evident in many sites throughout Africa.

The evidentiary support of the Out of Africa 2 model proves to be highly convincing and fascinating. The ground-breaking research of molecular geneticists, in particular, validates the legitimacy of this hypothesis, making it the strongest contender in answering where Homo sapiens sapiens originated. As Paul Pettitt suggests, ‘we are, it would appear, African in the main’ (Pettitt, P 2009i: 131).

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Cover Photo, Top Left: Skull of the fossil Homo sapiens sapiens from the Epipaleolithic of Combe Capelle. Gunter Bechly, Wikimedia Commons.

 

BIBLIOGRAPHY

Anderson-Mann, S. (2005/2006). Phylogenetic and phylogeographic analysis ofAfrican mitochondrial DNA variation. Available: http://www.biolog-e.leeds.ac.uk/Biolog-e/uploads/SadieAnderson-Mann.pdf , Last accessed: 10th Dec 2011.

Cruciani, F (2011). A revised root for the human Y chromosomal phylogenetic tree: the origin of patrilineal diversity in Africa. In: Wikipedia (2011).Y-chromosomal Adam. Available: http://en.wikipedia.org/wiki/Y-chromosomal_Adam , last accessed 10th Dec 2011.

EBO (2011). Parallel Evolution. Encyclopaedia Britannica Online.  Available: http://www.britannica.com/EBchecked/topic/442817/parallel-evolution  Last accessed 6th Dec 2011.

EP (2006 a-d):  Webster, J and Young, R (2006). Level 1 Module 2 –Early Prehistory. School of Archaeology and Ancient History, University of Leicester: 67-82

Foley, J (2003). Herto skulls (Homo sapiens idaltu).  Available: http://www.talkorigins.org/faqs/homs/herto.html, last accessed 11th Dec 2011.

Pettitt, P (2009 a-i). The rise of modern humans. In: Scaare, C. The Human Past. 2nd ed.  London: Thames and Hudson 124-173

Renfrew, C and Bahn, P (2008). Archaeology: Theories, Methods and Practice. 4th ed. London: Thames and Hudson:  464

Thames and Hudson (2008). Chapter 4:The Rise of Modern Humans. Available: http://www.thamesandhudsonusa.com/web/humanpast/summaries/ch04.html, last accessed 12th Dec 2011.

Wikipedia (2011). Multiregional origin of modern humans. Available: http://en.wikipedia.org/wiki/Multiregional_origin_of_modern_humans.html, Last accessed 5th Dec 2011.

Wolpoff, M and Thorne, A (1992). ‘The Multi-Regional Evolution of Humans’ Scientific American, 28-33

By Sophie Edwards

Sophie Edwards is a student of archaeology with the Univeristy of Leicester. She also volunteers with an archaeology team, currently excavating a site thought to be medieval in origin. She is most passionate about Classical civilisations, although Early prehistory is also an interest.  

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May 2001

Lucy is the common name of an Australopithecus afarensis specimen discovered in 1974 in Ethiopia. Lucy is estimated to have lived 3.2 million years ago. Cleveland Natural History Museum, photo by Andrew.

Around 30,000 years ago humans were anatomically and behaviorally similar throughout the world.

One of the most hotly debated issues in paleoanthropology (the study of human origins) focuses on the origins of modern humans, Homo sapiens.9,10,3,6,13,15,14 Roughly 100,000 years ago, the Old World was occupied by a morphologically diverse group of hominids. In Africa and the Middle East there was Homo sapiens; in Asia, Homo erectus; and in Europe, Homo neanderthalensis. However, by 30,000 years ago this taxonomic diversity vanished and humans everywhere had evolved into the anatomically and behaviorally modern form. The nature of this transformation is the focus of great deliberation between two schools of thought: one that stresses multiregional continuity and the other that suggests a single origin for modern humans.

Understanding the issue

Multiregional theory: homo erectus left Africa 2 mya to become homo sapiens in different parts of the world.

The Multiregional Continuity Model15 contends that after Homo erectus left Africa and dispersed into other portions of the Old World, regional populations slowly evolved into modern humans. This model contains the following components:

  • some level of gene flow between geographically separated populations prevented speciation, after the dispersal
  • all living humans derive from the species Homo erectus that left Africa nearly two million-years-ago
  • natural selection in regional populations, ever since their original dispersal, is responsible for the regional variants (sometimes called races) we see today
  • the emergence of Homo sapiens was not restricted to any one area, but was a phenomenon that occurred throughout the entire geographic range where humans lived

In contrast, the Out of Africa Model13 asserts that modern humans evolved relatively recently in Africa, migrated into Eurasia and replaced all populations which had descended from Homo erectus. Critical to this model are the following tenets:

Out of Africa theory: homo sapiens arose in Africa and migrated to other parts of the world to replace other hominid species, including homo erectus.

  • after Homo erectus migrated out of Africa the different populations became reproductively isolated, evolving independently, and in some cases like the Neanderthals, into separate species
  • Homo sapiens arose in one place, probably Africa (geographically this includes the Middle East)
  • Homo sapiens ultimately migrated out of Africa and replaced all other human populations, without interbreeding
  • modern human variation is a relatively recent phenomenon

The multiregional view posits that genes from all human populations of the Old World flowed between different regions and by mixing together, contributed to what we see today as fully modern humans. The replacement hypothesis suggests that the genes in fully modern humans all came out of Africa. As these peoples migrated they replaced all other human populations with little or no interbreeding.

To understand this controversy, the anatomical, archaeological, and genetic evidence needs to be evaluated.

Anatomical evidence

Sometime prior to 1 million years ago early hominids, sometimes referred to as Homo ergaster, exited Africa and dispersed into other parts of the Old World. Living in disparate geographical areas their morphology became diversified through the processes of genetic drift and natural selection.

  • In Asia these hominids evolved into Peking Man and Java Man, collectively referred to as Homo erectus.
  • In Europe and western Asia they evolved into the Neanderthals.

Neanderthals lived in quasi isolation in Europe during a long, relatively cool period that even included glaciations. Neanderthals are distinguished by a unique set of anatomical features, including:

  • a large, long, low cranial vault with a well-developed double-arched browridge

  • a massive facial skeleton with a very projecting mid-face, backward sloping cheeks, and large nasal aperture, with large nasal sinuses

  • an oddly shaped occipital region of the skull with a bulge or bun

  • molars with enlarged pulp chambers, and large, often very heavily worn incisors

  • a mandible lacking a chin and possessing a large gap behind the last molar

  • a massive thorax, and relatively short forearms and lower legs

  • although short in stature they possessed robustly built skeletons with thick walled limb bones

  • long clavicles and very wide scapulas

Homo sapiens is a separate species from Neanderthals and other hominids

By 130,000 years ago, following a prolonged period of independent evolution in Europe, Neanderthals were so anatomically distinct that they are best classified as a separate species — Homo neanderthalensis. This is a classic example of geographic isolation leading to a speciation event.

In contrast, at roughly the same time, in Africa, a body plan essentially like our own had appeared. While these early Homo sapiens were anatomically modern they were not behaviorally modern. It is significant that modern anatomy evolved prior to modern behavior. These early sapiens were characterized by:

  • a cranial vault with a vertical forehead, rounded occipital and reduced brow ridge
  • a reduced facial skeleton lacking a projecting mid-face
  • a lower jaw sporting a chin
  • a more modern, less robustly built skeleton

Hence, the anatomical and paleogeographic evidence suggests that Neanderthals and early modern humans had been isolated from one another and were evolving separately into two distinct species.

Archaeological evidence

Very interestingly, while Neanderthals and early Homo sapiens were distinguished from one another by a suite of obvious anatomical features, archaeologically they were very similar. Hominids of the Middle Stone Age of Africa (H. sapiens) and their contemporary Middle Paleolithic Neanderthals of Europe had artifact assemblages characterized as follows:

  • little variation in stone tool types, with a preponderance of flake tools that are difficult to sort into discrete categories

  • over long periods of time and wide geographical distances there was general similarity in tool kits

  • a virtual lack of tools fashioned out of bone, antler or ivory

  • burials lacked grave goods and signs of ritual or ceremony

  • hunting was usually limited to less dangerous species and evidence for fishing is absent

  • population densities were apparently low

  • no evidence of living structures exist and fireplaces are rudimentary

Homo sapiens exhibited technological skills around 50,000 years ago.

  • evidence for art or decoration is also lacking

The archaeological picture changed dramatically around 40-50,000 years ago with the appearance of behaviorally modern humans. This was an abrupt and dramatic change in subsistence patterns, tools and symbolic expression. The stunning change in cultural adaptation was not merely a quantitative one, but one that represented a significant departure from all earlier human behavior, reflecting a major qualitative transformation. It was literally a “creative explosion” which exhibited the “technological ingenuity, social formations, and ideological complexity of historic hunter-gatherers.”7 This human revolution is precisely what made us who we are today.

The appearance of fully modern behavior apparently occurred in Africa earlier than anywhere else in the Old World, but spread very quickly, due to population movements into other geographical regions. The Upper Paleolithic lifestyle, as it was called, was based essentially on hunting and gathering. So successful was this cultural adaptation that until roughly 11,000 years ago, hominids worldwide were subsisting essentially as hunter-gatherers.

In the Upper Paleolithic of Eurasia, or the Late Stone Age as it is called in Africa, the archaeological signature stands in strong contrast to that of the Middle Paleolithic/Middle Stone Age. It was characterized by significant innovation:

  • a remarkable diversity in stone tool types

  • tool types showed significant change over time and space

  • artifacts were regularly fashioned out of bone, antler and ivory, in addition to stone

  • stone artifacts were made primarily on blades and were easily classified into discrete categories, presumably reflecting specialized use

  • burials were accompanied by ritual or ceremony and contained a rich diversity of grave goods

  • living structures and well-designed fireplaces were constructed

  • hunting of dangerous animal species and fishing occurred regularly higher population densities

  • abundant and elaborate art as well as items of personal adornment were widespread

  • raw materials such as flint and shells were traded over some distances

Homo sapiens of the Upper Paleolithic/Late Stone Age was quintessentially modern in appearance and behavior. Precisely how this transformation occurred is not well understood, but it apparently was restricted to Homo sapiens and did not occur in Neanderthals. Some archaeologists invoke a behavioral explanation for the change. For example, Soffer11 suggests that changes in social relations, such as development of the nuclear family, played a key role in bringing about the transformation.

Social or biological changes may account for “smarter” hominids.

Klein7, on the other hand, proffers the notion that it was probably a biological change brought about by mutations that played the key role in the emergence of behaviorally modern humans. His biologically based explanation implies that a major neural reorganization of the brain resulted in a significant enhancement in the manner in which the brain processed information. This is a difficult hypothesis to test since brains do not fossilize. But it is significant that no changes are seen in the shape of the skulls between earlier and later Homo sapiens. It can only be surmised from the archaeological record, which contains abundant evidence for ritual and art, that these Upper Paleolithic/Late Stone Age peoples possessed language abilities equivalent to our own. For many anthropologists this represents the final evolutionary leap to full modernity.

Shortly after fully modern humans entered Europe, roughly 40,000 years ago, the Neanderthals began a fairly rapid decline, culminating in their disappearance roughly 30,000 years ago. Neanderthals were apparently no match for the technologically advanced fully modern humans who invaded Europe and evidence for interbreeding of these two types of hominids is equivocal.

Genetic evidence

Investigation of the patterns of genetic variation in modern human populations supports the view that the origin of Homo sapiens is the result of a recent event that is consistent with the Out of Africa Model.

  • Studies of contemporary DNA, especially mitochondrial DNA (mtDNA) which occurs only in the cellular organelles called mitochondria, reveal that humans are astonishingly homogeneous, with relatively little genetic variation.1,5

  • The high degree of similarity between human populations stands in strong contrast to the condition seen in our closest living relatives, the chimpanzees.2 In fact, there is significantly more genetic variation between two individual chimpanzees drawn from the same population than there is between two humans drawn randomly from a single population. Furthermore, genetic variation between populations of chimpanzees is enormously greater than differences between European, Asian and African human populations.

Africans display higher genetic variation than other populations, supporting the idea that they were the first modern humans.

  • In support of an African origin for Homo sapiens the work of Cann and Wilson1 has demonstrated that the highest level of genetic variation in mtDNA occurs in African populations. This implies that Homo sapiens arose first in Africa and has therefore had a longer period of time to accumulate genetic diversity. Using the genetic distance between African populations and others as a measure of time, they furthermore suggested that Homo sapiens arose between 100,000 and 400,000 years ago in Africa.

  • The low amount of genetic variation in modern human populations suggests that our origins may reflect a relatively small founding population for Homo sapiens. Analysis of mtDNA by Rogers and Harpending12 supports the view that a small population of Homo sapiens, numbering perhaps only 10,000 to 50,000 people, left Africa somewhere between 50,000 and 100,000 years ago.

  • Scientists recently succeeded in extracting DNA from several Neanderthal skeletons.8 After careful analysis of particularly the mtDNA, but now also some nuclear DNA, it is apparent that Neanderthal DNA is very distinct from our own. In assessing the degree of difference between DNA in Neanderthals and modern humans, the authors suggest that these two lineages have been separated for more than 400,000 years.

Although in its infancy, such genetic studies support the view that Neanderthals did not interbreed with Homo sapiens who migrated into Europe. It is, therefore, highly likely that modern humans do not carry Neanderthal genes in their DNA.

Additional considerations

The chronology in the Middle East does not support the Multiregional Model where Neanderthals and anatomically modern humans overlapped for a long period of time.

  • Cave sites in Israel, most notably Qafzeh and Skhul date to nearly 100,000 years and contain skeletons of anatomically modern humans. Furthermore, Neanderthal remains are known from sites such as the 110,000-year-old Tabun cave, which predates the earliest Homo sapiens by about 10,000 years in the region.

Neanderthals and modern humans coexisted in some parts of the world for thousands of years.

  • The presence of Neanderthals at two other caves in Israel, Amud and Kebara, dated to roughly 55,000 years means that Neanderthals and Homo sapiens overlapped in this region for at least 55,000 years. Therefore, if Homo sapiens were in this region for some 55,000 years prior to the disappearance of the Neanderthals, there is no reason to assume that Neanderthals evolved into modern humans.

  • Archaeological evidence from Europe suggests that Neanderthals may have survived in the Iberian Peninsula until perhaps as recently as 30,000 to 35,000 years ago. Fully modern humans first appear in Europe at around 35,000-40,000 years ago, bringing with them an Upper Paleolithic tool tradition referred to as the Aurignacian. Hence, Neanderthals and fully modern humans may have overlapped for as much as 10,000 years in Europe. Again, with fully modern humans on the scene, it is not necessary to have Neanderthals evolve into modern humans, further bolstering the view that humans replaced Neanderthals.

Neanderthals probably did not breed with modern humans but they borrowed some of their tools and skills

  • The situation in southern France is, however, not quite as clear. Here, at several sites, dating to roughly 40,000 years there is evidence of an archaeological industry called the Châtelperronian that contains elements of Middle and Upper Paleolithic artifacts. Hominids from these sites are clearly Neanderthals, sparking speculation that the Châtelperronian is an example of Neanderthals mimicking the culture of modern humans. The lack of anatomical intermediates at these sites, suggests that if Neanderthals did encounter and borrow some technology from Homo sapiens, they did not interbreed.

  • A potential 24,500-year-old Neanderthal/sapiens hybrid was announced from the site of Lagar Velho, Portugal.4 This 4-year-old has a short, squat body like a Neanderthal, but possesses an anatomically modern skull. There are a number of problems with interpreting this find as a Neanderthal/sapiens hybrid.14 First of all, as a hybrid it should have a mixture of traits throughout its body and not possess the body of a Neanderthal and skull of a modern human. For example, if we look at hybrids of lions and tigers they do not possess the head of one species and the body of the other, but exhibit a morphological mixture of the two species. Secondly, and more importantly, acceptance of this specimen as a hybrid would suggest that Neanderthal traits had been retained for some 6,000 to 10,000 years after Neanderthals went extinct, which is highly unlikely. This is theoretically unlikely since Neanderthal traits would have been genetically swamped by the Homo sapiens genes over such a protracted period of time.

  • Proponents of the Multiregional Model, such as Milford Wolpoff, cite evidence in Asia of regional continuity. They see an evolutionary link between ancient Homo erectus in Java right through to Australian aborigines. A possible problem with this view is that recent dating of late surviving Homo erectus in Indonesia suggests that they survived here until 50,000 years ago, which is potentially when fully modern humans may have arrived in the region from Africa.

  • China may contain the best evidence for supporting the Multiregional Model. Here there are discoveries of a couple of skulls dated to roughly 100,000 years ago that seem to possess a mixture of classic Homo erectus and Homo sapiens traits. Better geological dating and more complete specimens are needed to more fully assess this possibility.

Conclusion

For the moment, the majority of anatomical, archaeological and genetic evidence gives credence to the view that fully modern humans are a relatively recent evolutionary phenomenon. The current best explanation for the beginning of modern humans is the Out of Africa Model that postulates a single, African origin for Homo sapiens. The major neurological and cultural innovations that characterized the appearance of fully modern humans has proven to be remarkably successful, culminating in our dominance of the planet at the expense of all earlier hominid populations.

© 2001, American Institute of Biological Sciences. Educators have permission to reprint articles for classroom use; other users, please contact editor@actionbioscience.org for reprint permission. See reprint policy.

Paleoanthropologist Donald C. Johanson, is professor of anthropology and Director of the Institute of Human Origins at Arizona State University. He is best known for his discovery of “Lucy”, a 3.2 million-year old Australopithecus afarensis skeleton he found in 1974 in Ethiopia. His books include Lucy: The Beginnings of Humankind and, most recently, From Lucy to Language. Dr. Johanson hosted the Emmy-nominated NOVA television series In Search of Human Origins.
http://iho.asu.edu/people_admin

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Origins of Modern Humans: Multiregional or Out of Africa?

Understanding Evolution

Your one-stop source for information on evolution. Learn the facts in Evolution 101, browse the resource library, read about evolution in the news, or discover a wealth of materials to help educate others about evolution and related concepts—it’s all right here! http://evolution.berkeley.edu

Mitochondrial DNA Clarifies Human Evolution

A companion article on this site about how genetic research supports (or doesn’t support) the different views on human origins.
http://www.actionbioscience.org/evolution/ingman.html

Institute of Human Origins

The Institute of Human Origins’ web site is a comprehensive site on human origins and has a special segment on the emergence of modern humans.
http://www.becominghuman.org

The Biological Anthropology Web

“Information on and discussions of topics related to broadly defined aspects of biological & cultural human variation & adaptation.”
http://www.bioanth.org/

Walking with Cavemen

The BBC challenges you to put your skills to the test in their interactive quiz or play the seven stages of evolution (click on the “cavemen challenge” to begin). Also check out the in-depth information in the side-bar menu (e.g., family tree) or click on a time period near top of page.
http://www.bbc.co.uk/science/cavemen/

Smithsonian Institution

Its Human Origins Program covers all aspects of evolutionary science, with a Hall of Human Ancestors, a family tree, and What’s Hot! in Paleoanthropology which looks at recent findings.
www.mnh.si.edu/anthro/humanorigins

Read a book

  • » From Lucy to Language by D.C. Johanson and B. Edgar (Simon and Schuster, 1996).
  • » The Fossil Trail: How We Know What We Think We Know about Human Evolution by I. Tattersall (Oxford University Press, 1995).
  • » Extinct Humans by I. Tattersall and J. H. Schwartz (Westview Press, 2000).

A Multimedia Guide to the Fossil Record

A learning tool designed for undergraduate students, this CD uses 3-D, photo-realistic images of fossils to teach students about ten important milestones in human evolution, from the appearance of the primates to the demise of the Neanderthals. An interesting way for anyone to learn about human evolution.
http://www.anth.ucsb.edu/projects/human/

Visit a museum

Visit an online museum to learn more about the evolutionary history of humans. Click on these categories in the list of museum types: anthropology, archaeology, evolution, fossils, natural history. Is there such a museum in your area? Why not spend some time there, too?
http://www.museumstuff.com/museums/types/science.html

ActionBioscience.org original lesson

This lesson has been written by a science educator to specifically accompany the above article. It includes article content and extension questions, as well as activity handouts for different grade levels.

Lesson Title: Roots: The Ancestry of Modern People
Levels: high school - undergraduate
Summary: This lesson examines the two main models of the origin of modern humans. Students can map the movements of early humans, consider what it takes to be a paleoanthropologist, write a news flash about Lucy’s discovery, chart a book plot about the adventures of an early hominid, create a sketchbook of hominid fossils… and more!

Download/view lesson.
(To open the lesson’s PDF file, you need Adobe Acrobat Reader free software.)

Useful links for educators

In addition to the links in the “learn more” section above:

  • » The Leakey Foundation
    The official site of one of the foundations established by Dr. Louis Leakey, one of the world’s best known paleoanthropologists. You may want your students to listen to the audio archives of scientists and their fossil discoveries.
    http://www.leakeyfoundation.org/

Useful links for student research

In addition to the links in the “learn more” section above:

  1. Cann, R.L., M. Stoneking, and A.C. Wilson. 1987. “Mitochondrial DNA and human evolution.” Nature, 325:32-36.
  2. Cavalli-Sforza, L.L. 2000. Genes, Peoples, and Languages. New York. North Point Press.
  3. Clark, G.A. and C.M. Willermet (eds.). 1997. Conceptual Issues in Modern Human Origins Research. New York. Aldine de Gruyter.
  4. Duarte, C, J. Maurício, P.B. Pettitt, P. Souto, E. Trinkaus, H. van der Plicht, and J. Zilhão. 1999. “The early Upper Paleolithic human skeleton from the Abrigo do Lagar Velho (Portugal) and modern human emergence in Iberia.” Proc. Natl. Acad. Sci. USA, 96:7604-7609.
  5. Ingman, M., H. Kaessmann, S. Pääbo, and U. Gyllensten. 2000. “Mitochondrial genome variation and the origin of modern humans.” Nature, 408:708-713.
  6. Klein, R.. 1999. The Human Career. Chicago. University of Chicago Press.
  7. Klein, R. 2000. “Archaeology and the evolution of human behavior.” Evolutionary Anthropology, 9:17-36.
  8. Krings, M, H. Geisert, R.W. Schmitz, H Krainitzki, and S. Pääbo 1999. “DNA sequence of the mitochondrial hypervariable region II from the Neanderthal type specimen.” Proc. Natl. Acad. Sci., 96: 5581-5585.
  9. Nitecki, M.H. and D.V. Nitecki (eds.). 1994. Origins of Anatomically Modern Humans. New York. Plenum Press.
  10. Smith, F.H. and F. Spencer (eds.). 1984. The Origins of Modern Humans: A World Survey of the Fossil Evidence. New York. Liss.
  11. Soffer, O. 1990. “Before Beringia: Late Pleistocene biosocial transformations and the colonization of northern Eurasia.” In: “Chronostratigraphy of the Paleolithic in North, Central, East Asia and America.” Novosibirisk. Acad. Of Sci. of the USSR.
  12. Rogers, A.R. and H.C. Harpending. 1992. “Population growth makes waves in the distribution of pairwise genetic differences.” Mol. Biol. Evol., 9:552-569.
  13. Stringer , C. and R. McKie. 1996. African Exodus: The Origins of Modern Humanity. New York: Henry Holt.
  14. Tattersall, I. and J.H. Schwartz. 1999. “Hominids and hybrids: The place of Neanderthals in human evolution.” Proc. Natl. Acad. Sci. USA, 96:7117-7119.
  15. Wolpoff, M.H. and R. Caspari. 1996. Race and Human Evolution: A Fatal Attraction. New York. Simon and Schuster.
  16. Wolpoff, M.H., J. Hawks, D.W. Frayer and K. Hunley. 2001. “Modern human ancestry at the peripheries: A test of the replacement theory.” Science, 291:293-297.

author glossary

Gene flow - the flow of genes from one population to another.
Genetic drift - the change of gene frequency from one generation to another caused by the cumulative effects of random fluctuations, rather than by natural selection.
Mitochondrial DNA - the DNA found only in the mitochondria (the powerhouses of the cell) and inherited only from the mother.
Morphology - the scientific study of the form and structure of organisms.
Paleoanthropology - the study of human origins, the study of the fossil and cultural remains of extinct human ancestors.
Taxonomy - the classification of organisms into groups according to their relationships and the ordering of these groups into a hierarchical arrangement.

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