Recent African Origins or Regional Evolution?

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Information about Recent African Origins or Regional Evolution?

Published on March 23, 2009

Author: PaulVMcDowell

Source: slideshare.net

Description

Compares the two major models of human migration and the means of testing them.

Recent African Origins or Regional Evolution? Where did Modern Humans Come From, and When?

Human Origins: An Acrimonious Debate There is a longstanding debate as to how we got to be we, namely become modern Homo sapiens? Why do the experts, whom we are supposed to respect for their careful research, differ so intensely that sparks fly?

There is a longstanding debate as to how we got to be we, namely become modern Homo sapiens?

Why do the experts, whom we are supposed to respect for their careful research, differ so intensely that sparks fly?

Why the Debate: Several Reasons The evidence itself is fragmentary, as you’ve seen in the past lessons; we just don’t have complete skulls or postcranial skeletons handed to us on a platter Therefore we have to make inferences from our bone fragments, and different experts make different inferences from those bone fragments Every expert comes to the field and the lab with her or his own assumptions

The evidence itself is fragmentary, as you’ve seen in the past lessons; we just don’t have complete skulls or postcranial skeletons handed to us on a platter

Therefore we have to make inferences from our bone fragments, and different experts make different inferences from those bone fragments

Every expert comes to the field and the lab with her or his own assumptions

Points of Agreement There is one agreement: almost all paleoanthropologists agree that we evolved from Homo erectus They also agree that Homo erectus migrated from Africa into Asia and Europe This is where the experts split into two camps—When and where did we evolve from Homo erectus ?

There is one agreement: almost all paleoanthropologists agree that we evolved from Homo erectus

They also agree that Homo erectus migrated from Africa into Asia and Europe

This is where the experts split into two camps—When and where did we evolve from Homo erectus ?

The Recent African and Multiregional Evolution Models Did our ancestors evolve at different places around the Old World from Homo erectus? That is known as the Multiregional Evolution Model Or did they all evolve from Homo erectus in Africa? That is known as the Recent African Origin model, because we originated from Africa only in the past one or two hundred thousand years BP (before the present) This is also known as the Out of Africa model.

Did our ancestors evolve at different places around the Old World from Homo erectus?

That is known as the Multiregional Evolution Model

Or did they all evolve from Homo erectus in Africa?

That is known as the Recent African Origin model, because we originated from Africa only in the past one or two hundred thousand years BP (before the present)

This is also known as the Out of Africa model.

The Two Models Compared Left: Multiregional Hypothesis: Homo erectus migrates to Asia and Europe and evolves in each region into Homs sapiens . The little arrows indicate interbreeding across the regions, keeping our species intact.. Right: Recent African Origin (Out of Africa) Hypothesis: Homo erectus evolves into Homo sapiens, then migrates to the rest of the Old World—and the new one

Left: Multiregional Hypothesis: Homo erectus migrates to Asia and Europe and evolves in each region into Homs sapiens .

The little arrows indicate interbreeding across the regions, keeping our species intact..

Right: Recent African Origin (Out of Africa) Hypothesis: Homo erectus evolves into Homo sapiens, then migrates to the rest of the Old World—and the new one

Multiregional Evolution Model This map depicts humans evolving from regional points and migrating from there What prevents speciation, of humans from becoming new species? Milford Wolpoff (lower left) has an answer: Whatever else hominins may do, they always interbreed. Thus they maintain control over, or prevent, speciation Alan Thorne (lower right) traces Homo erectus ‘s transition to Homo Sapiens in Southeast Asia

This map depicts humans evolving from regional points and migrating from there

What prevents speciation, of humans from becoming new species? Milford Wolpoff (lower left) has an answer:

Whatever else hominins may do, they always interbreed.

Thus they maintain control over, or prevent, speciation

Alan Thorne (lower right) traces Homo erectus ‘s transition to Homo Sapiens in Southeast Asia

Recent African Origin Model This map places modern human origins, according to one conception, somewhere in the pink shaded area of S. and E. Africa Then humans migrate in waves: the darker the red, the more recent the waves. Ian Tattersall (with bony colleague) argues the following; Modern Homo sapiens evolved in Africa around 200,000 BP They migrated to Europe and Asia They displaced archaic H. sapiens including H. neanderthalensis Modern and archaic forms did not interbreed, extinguishing the latter

This map places modern human origins, according to one conception, somewhere in the pink shaded area of S. and E. Africa

Then humans migrate in waves: the darker the red, the more recent the waves.

Ian Tattersall (with bony colleague) argues the following;

Modern Homo sapiens evolved in Africa around 200,000 BP

They migrated to Europe and Asia

They displaced archaic H. sapiens including H. neanderthalensis

Modern and archaic forms did not interbreed, extinguishing the latter

Partial Replacement Model: A Middle Ground? Gunter Br äuer, Univ. of Hamburg, Germany Modern H. sapiens arose in Africa around 100,000 BP They both replaced and interbred with archaic sapient forms Through interbreeding, modern populations gradually replaced the premodern hominins Fred Smith: replacement occurred as much through gene flow as through migration: they let the genes do the walking

Gunter Br äuer, Univ. of Hamburg, Germany

Modern H. sapiens arose in Africa around 100,000 BP

They both replaced and interbred with archaic sapient forms

Through interbreeding, modern populations gradually replaced the premodern hominins

Fred Smith: replacement occurred as much through gene flow as through migration: they let the genes do the walking

Testing the Models It is very well to speculate on and interpret the two models How do we test them? We offer one set of tests to compare the hypotheses generated by the two models We then show how that one test alone is fraught with ambiguities of the data—the fragmented hominin remains.

It is very well to speculate on and interpret the two models

How do we test them?

We offer one set of tests to compare the hypotheses generated by the two models

We then show how that one test alone is fraught with ambiguities of the data—the fragmented hominin remains.

Out-of-Africa Model: Test Expectations I Oldest modern sapient fossils should be found only in Africa (see model to the right) Transitional forms (e.g. H. Heidelbergensis) should be found only in Africa Elsewhere, emigrant modern humans should coexist with archaic humans until the latters’ extinction

Oldest modern sapient fossils should be found only in Africa (see model to the right)

Transitional forms (e.g. H. Heidelbergensis) should be found only in Africa

Elsewhere, emigrant modern humans should coexist with archaic humans until the latters’ extinction

Out-of-Africa Model: Test Expectations II There should be a break between premodern (H. heidelbergensis and earlier forms) and modern fossil humans outside Africa Modern human material cultures (e.g. tools) should make a sudden appearance outside Africa, with no transitional forms Modern humans should be genetically distinct from premodern humans outside Africa

There should be a break between premodern (H. heidelbergensis and earlier forms) and modern fossil humans outside Africa

Modern human material cultures (e.g. tools) should make a sudden appearance outside Africa, with no transitional forms

Modern humans should be genetically distinct from premodern humans outside Africa

Multiregional Evolutionary Model: Test Expectations I Early modern human fossils should be found across all or many regions, none much older than the others (left model) Intermediate humans should be found across the regions because evolution occurred everywhere. Premodern features should grade into modern forms everywhere as modern genes replace premodern ones (e.g. reduction of prognathism)

Early modern human fossils should be found across all or many regions, none much older than the others (left model)

Intermediate humans should be found across the regions because evolution occurred everywhere.

Premodern features should grade into modern forms everywhere as modern genes replace premodern ones (e.g. reduction of prognathism)

Multiregional Evolutonary Model: Test Expectation II Local skeletal traits should show continuity between modern and premodern forms everywhere There should be a continuous development between premodern and modern material cultural remains There should be genetic continuity between modern and premodern forms in every region

Local skeletal traits should show continuity between modern and premodern forms everywhere

There should be a continuous development between premodern and modern material cultural remains

There should be genetic continuity between modern and premodern forms in every region

Shifting Evidence Klases River Mouth, South Africa yielded the following finds: Fragments of modern skulls and a jaw with a modern chin (upper left) The jaw and fragments were dated 90,000 years BP, the oldest up to that time (1970s) The find would confirm the RAO hypothesis Then a modern skull was found in Liujiang, China (lower left) in 1958, dated 20 to 30,000 BP An analysis in 2002, however, dated the skull 100,000 years BP, favoring the Multiregional Evolution model Later finds place a modern find in Omo, Ethiopia, at 195,000 years BP, favoring the RAO Model—for now.

Klases River Mouth, South Africa yielded the following finds:

Fragments of modern skulls and a jaw with a modern chin (upper left)

The jaw and fragments were dated 90,000 years BP, the oldest up to that time (1970s)

The find would confirm the RAO hypothesis

Then a modern skull was found in Liujiang, China (lower left) in 1958, dated 20 to 30,000 BP

An analysis in 2002, however, dated the skull 100,000 years BP, favoring the Multiregional Evolution model

Later finds place a modern find in Omo, Ethiopia, at 195,000 years BP, favoring the RAO Model—for now.

Current Status of the Models: Modern Homo sapiens At the moment, multiple sites indicate that African sapient sites are older Homo sapiens skulls are oldest in Africa They range between 100,000 and 200, 000 years BP, including the Omo find Israel has remains ranging between 92,000 and 120,000 BP European skulls range between 10,000 and 27,000 BP China’s range is 10,000 to 100,000 BP Australian skulls range from 40,000 upward So far these data support the Recent African Origins Model

At the moment, multiple sites indicate that African sapient sites are older

Homo sapiens skulls are oldest in Africa

They range between 100,000 and 200, 000 years BP, including the Omo find

Israel has remains ranging between 92,000 and 120,000 BP

European skulls range between 10,000 and 27,000 BP

China’s range is 10,000 to 100,000 BP

Australian skulls range from 40,000 upward

So far these data support the Recent African Origins Model

Current Status of the Models: “Archaic Homo sapiens ” The same pattern applies to Homo heidelbergensis , or Archaic Homo sapiens African remains vary between 400,000 and 700,000 BP European remains vary between 160,000 and 475,000 BP (780,000 in Spain) China and India: 130,000-200,000 BP These fit the pattern of the Recent African Origins model.

The same pattern applies to Homo heidelbergensis , or Archaic Homo sapiens

African remains vary between 400,000 and 700,000 BP

European remains vary between 160,000 and 475,000 BP (780,000 in Spain)

China and India: 130,000-200,000 BP

These fit the pattern of the Recent African Origins model.

Typological Ambiguities Also open to controversy is what constitutes modern Homo sapiens Harold Dibble argues that typologies often lead us down blind alleys We often find differences that aren’t really there , creating even more squabbles—like this one or the one about the human status of Neanderthals Artist’s conception of Homo heidelbergensis (lower left)—or is it Homo sapiens ?

Also open to controversy is what constitutes modern Homo sapiens

Harold Dibble argues that typologies often lead us down blind alleys

We often find differences that aren’t really there , creating even more squabbles—like this one or the one about the human status of Neanderthals

Artist’s conception of Homo heidelbergensis (lower left)—or is it Homo sapiens ?

Taxonomic Questions This comparison of a Neanderthal (left) and human skeleton reflects a major controversy about human typology Wolpoff goes so far as to suggest that Homo erectus (lower left) and Homo sapiens (lower right( could be one species As the clichés have it, you be the judge: From the two sets of pictures, does Wolpoff make a prima facie case for his one-species argument?

This comparison of a Neanderthal (left) and human skeleton reflects a major controversy about human typology

Wolpoff goes so far as to suggest that Homo erectus (lower left) and Homo sapiens (lower right( could be one species

As the clichés have it, you be the judge:

From the two sets of pictures, does Wolpoff make a prima facie case for his one-species argument?

Testing the Model Are the oldest modern forms found in Africa or are they also found in Europe and Asia? Are transitional forms found only in Africa or are they also found in Europe and Asia? What’s the evidence from genetic mutation? Mitochondrial DNA in the female lineage> Y Chromosomes? Is the transformation from archaic to modern forms sudden or gradual outside Africa? What do the archaeological finds say?

Are the oldest modern forms found in Africa or are they also found in Europe and Asia?

Are transitional forms found only in Africa or are they also found in Europe and Asia?

What’s the evidence from genetic mutation?

Mitochondrial DNA in the female lineage>

Y Chromosomes?

Is the transformation from archaic to modern forms sudden or gradual outside Africa?

What do the archaeological finds say?

Case Example: Mitochondrial DNA Principles of mitorchorndral DNA (mDNA) tests mDNA samples only from living persons mDNA is used to retrodict past mutations mDNA is passed only by women Sperm leaves behind all its mDNA Fetus inherits mDNA only from ovum Number of mDNA mutations indicates antiquity of species

Principles of mitorchorndral DNA (mDNA) tests

mDNA samples only from living persons

mDNA is used to retrodict past mutations

mDNA is passed only by women

Sperm leaves behind all its mDNA

Fetus inherits mDNA only from ovum

Number of mDNA mutations indicates antiquity of species

Out of Africa: Procedures Rebecca Cann and colleagues: Sampled 147 women mDNA shows little diversity Sample was to be worldwide Africans should show the most mutations New Guinea (NG)/Australian, dated 80K BP, included Africans showed 3 times mutation of NG./Australians Other populations similarly sampled Results tended to support claim Mutations traceable to a single African female Hence, “Mitochondral Eve

Rebecca Cann and colleagues:

Sampled 147 women

mDNA shows little diversity

Sample was to be worldwide

Africans should show the most mutations

New Guinea (NG)/Australian, dated 80K BP, included

Africans showed 3 times mutation of NG./Australians

Other populations similarly sampled

Results tended to support claim

Mutations traceable to a single African female

Hence, “Mitochondral Eve

Out of Africa: mDNA a flawed methodology Nature of the flaws Sample was too small: 147 out of 2 billion All “African” women were American Potential admixture with Europeans, Native Americans, and Asians Order of data input influenced results Alan Templeton reran the tests Found mutation rates equal for Africans, Europeans, and Asian Supports mulitregional theory

Nature of the flaws

Sample was too small: 147 out of 2 billion

All “African” women were American

Potential admixture with Europeans, Native Americans, and Asians

Order of data input influenced results

Alan Templeton reran the tests

Found mutation rates equal for Africans, Europeans, and Asian

Supports mulitregional theory

Out of Africa Theory: Retests of mDNA Laurence Excoffier & Andre Langanay Tested larger sample Africans from Africa exhibited less diversity Than European and Asians. Cann and colleagues ran a retest Sample much larger--5,000 Africans from African included Support more modest Africans showed more diversity But the variations were not statistically significant

Laurence Excoffier & Andre Langanay

Tested larger sample

Africans from Africa exhibited less diversity

Than European and Asians.

Cann and colleagues ran a retest

Sample much larger--5,000

Africans from African included

Support more modest

Africans showed more diversity

But the variations were not statistically significant

Mitochondrial DNA: General Results, If Any There might have been several migrations out of Africa, not just one. The migrations could have taken place various times from 2 billions years BP—to the present Thus it is not surprising that Templeton found varied and even contradictory results The genetics of the world population isn’t all that diverse in the first place. For full argumentation, see pp. 331-344.

There might have been several migrations out of Africa, not just one.

The migrations could have taken place various times from 2 billions years BP—to the present

Thus it is not surprising that Templeton found varied and even contradictory results

The genetics of the world population isn’t all that diverse in the first place.

For full argumentation, see pp. 331-344.

Conclusion Fragmentary data makes the controversy less than conclusive. It depends on our typology, from Tattersall’s extreme splitter taxonomy to Wolpoff’s lumper’s imagination. And how we interpret our finds in relation to the typology we have accepted. The artists’ conceptions involve knowledge of human/hominin anatomy with a great deal of subjective interpretation. Finally, DNA results are too varied to be conclusive—mtDNA or Y chromosomes

Fragmentary data makes the controversy less than conclusive.

It depends on our typology, from Tattersall’s extreme splitter taxonomy to Wolpoff’s lumper’s imagination.

And how we interpret our finds in relation to the typology we have accepted.

The artists’ conceptions involve knowledge of human/hominin anatomy with a great deal of subjective interpretation.

Finally, DNA results are too varied to be conclusive—mtDNA or Y chromosomes

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