Origins of Modern Humans: Multiregional or Out of Africa?

Donald Johanson

An ActionBioscience.org original article

There are two theories about the origin of modern humans: 1) they arose in one place — Africa and 2) pre-modern humans migrated from Africa to become modern humans in other parts of the world. Most evidence points to the first theory because:

May 2001

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

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.

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:

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.

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.

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:

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:

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:

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

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:

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.

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

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.

Neanderthals and modern humans coexisted in some parts of the world for thousands of years.
Neanderthals probably did not breed with modern humans but they borrowed some of their tools and skills

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.

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://www.mnsu.edu/emuseum/information/biography/fghij/johanson_donald.html



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

Human evolution chart

Click on this interactive chart of human evolution, stretching from 5 million years ago to the present, to learn about different hominid species.
http://www.geocities.com/palaeoanthropology/timeline.html

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

getinvolved links

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

articlereferences

  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.

educatorresources

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:

Useful links for student research

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



On the web at: http://www.actionbioscience.org/evolution/johanson.html
authorbio: 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.