Recent African Recent African Origins or Origins or Regional Regional

Evolution?Evolution?Where did Modern Humans Where did Modern Humans Come From, and When?Come From, and When?

Human Origins: An Human Origins: An Acrimonious DebateAcrimonious Debate

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

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

Why the Debate: Several Why the Debate: Several ReasonsReasons

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

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

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

Points of AgreementPoints of Agreement

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

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

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

The Recent African and The Recent African and Multiregional Evolution Multiregional Evolution

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

That is known as the Multiregional That is known as the Multiregional Evolution ModelEvolution Model

Or did they all evolve from Or did they all evolve from Homo erectusHomo erectus in Africa?in Africa?

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

This is also known as the Out of Africa This is also known as the Out of Africa model. model.

The Two Models ComparedThe Two Models Compared

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

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

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

Multiregional Evolution Multiregional Evolution ModelModel

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

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

Whatever else hominins may Whatever else hominins may do, they always interbreed. do, they always interbreed.

Thus they maintain control Thus they maintain control over, or prevent, speciationover, or prevent, speciation

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

Recent African Origin Recent African Origin ModelModel

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

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

Ian Tattersall (with bony Ian Tattersall (with bony colleague) argues the following;colleague) argues the following;

Modern Modern Homo sapiensHomo sapiens evolved in evolved in Africa around 200,000 BPAfrica around 200,000 BP

They migrated to Europe and AsiaThey migrated to Europe and Asia They displaced archaic They displaced archaic H. sapiens H. sapiens

including including H. neanderthalensis H. neanderthalensis Modern and archaic forms did not Modern and archaic forms did not

interbreed, extinguishing the interbreed, extinguishing the latterlatter

Partial Replacement Model: Partial Replacement Model: A Middle Ground?A Middle Ground?

Gunter BrGunter Bräuer, Univ. of Hamburg, Germanyäuer, Univ. of Hamburg, Germany Modern Modern H. sapiensH. sapiens arose in Africa around arose in Africa around

100,000 BP100,000 BP They both replaced and interbred with They both replaced and interbred with

archaic sapient formsarchaic sapient forms Through interbreeding, modern populations Through interbreeding, modern populations

gradually replaced the premodern homininsgradually replaced the premodern hominins Fred Smith: replacement occurred as much Fred Smith: replacement occurred as much

through gene flow as through migration: through gene flow as through migration: they let the genes do the walking they let the genes do the walking

Testing the ModelsTesting the Models

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

How do we test them?How do we test them? We offer one set of tests to compare We offer one set of tests to compare

the hypotheses generated by the two the hypotheses generated by the two modelsmodels

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

Out-of-Africa Model: Test Out-of-Africa Model: Test Expectations IExpectations I

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

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

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

Out-of-Africa Model: Test Out-of-Africa Model: Test Expectations IIExpectations II

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

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

Modern humans should be genetically Modern humans should be genetically distinct from premodern humans outside distinct from premodern humans outside AfricaAfrica

Multiregional Evolutionary Multiregional Evolutionary Model: Test Expectations IModel: Test Expectations I

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

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

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

Multiregional Multiregional Evolutonary Model: Test Evolutonary Model: Test

Expectation IIExpectation II Local skeletal traits should show Local skeletal traits should show

continuity between modern and continuity between modern and premodern forms everywherepremodern forms everywhere

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

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

Shifting EvidenceShifting Evidence Klases River Mouth, South Africa yielded Klases River Mouth, South Africa yielded

the following finds:the following finds: Fragments of modern skulls and a jaw with Fragments of modern skulls and a jaw with

a modern chin (upper left)a modern chin (upper left) The jaw and fragments were dated 90,000 The jaw and fragments were dated 90,000

years BP, the oldest up to that time (1970s)years BP, the oldest up to that time (1970s) The find would confirm the RAO hypothesisThe find would confirm the RAO hypothesis Then a modern skull was found in Liujiang, Then a modern skull was found in Liujiang,

China (lower left) in 1958, dated 20 to China (lower left) in 1958, dated 20 to 30,000 BP30,000 BP

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

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

Current Status of the Current Status of the Models: Modern Models: Modern Homo Homo

sapienssapiens At the moment, multiple sites indicate that At the moment, multiple sites indicate that

African sapient sites are olderAfrican sapient sites are older Homo sapiens Homo sapiens skulls are oldest in Africaskulls are oldest in Africa They range between 100,000 and 200, 000 They range between 100,000 and 200, 000

years BP, including the Omo findyears BP, including the Omo find Israel has remains ranging between 92,000 and Israel has remains ranging between 92,000 and

120,000 BP120,000 BP European skulls range between 10,000 and European skulls range between 10,000 and

27,000 BP27,000 BP China’s range is 10,000 to 100,000 BPChina’s range is 10,000 to 100,000 BP Australian skulls range from 40,000 upwardAustralian skulls range from 40,000 upward So far these data support the Recent African So far these data support the Recent African

Origins ModelOrigins Model

Current Status of the Current Status of the Models: “Archaic Models: “Archaic Homo Homo

sapienssapiens”” The same pattern applies to The same pattern applies to Homo Homo

heidelbergensisheidelbergensis, or Archaic , or Archaic Homo Homo sapienssapiens

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

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

China and India: 130,000-200,000 BPChina and India: 130,000-200,000 BP These fit the pattern of the Recent These fit the pattern of the Recent

African Origins model. African Origins model.

Typological AmbiguitiesTypological Ambiguities Also open to controversy is Also open to controversy is

what constitutes modern what constitutes modern Homo sapiensHomo sapiens

Harold Dibble Harold Dibble argues that argues that typologies often lead us down typologies often lead us down blind alleysblind alleys

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

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

Taxonomic QuestionsTaxonomic Questions This comparison of a This comparison of a

Neanderthal (left) and Neanderthal (left) and human skeleton reflects a human skeleton reflects a major controversy about major controversy about human typologyhuman typology

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

As the clichés have it, you be As the clichés have it, you be the judge:the judge:

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

Testing the ModelTesting the Model Are the oldest modern forms found in Africa Are the oldest modern forms found in Africa

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

are they also found in Europe and Asia?are they also found in Europe and Asia? What’s the evidence from genetic mutation?What’s the evidence from genetic mutation? Mitochondrial DNA in the female lineage>Mitochondrial DNA in the female lineage> Y Chromosomes?Y Chromosomes? Is the transformation from archaic to Is the transformation from archaic to

modern forms sudden or gradual outside modern forms sudden or gradual outside Africa?Africa?

What do the archaeological finds say?What do the archaeological finds say?

Case Example: Case Example: Mitochondrial DNAMitochondrial DNA

Principles of mitorchorndral Principles of mitorchorndral DNA (mDNA) testsDNA (mDNA) tests

mDNA samples only from mDNA samples only from living personsliving persons

mDNA is used to retrodict mDNA is used to retrodict past mutationspast mutations

mDNA is passed only by mDNA is passed only by womenwomen

Sperm leaves behind all its Sperm leaves behind all its mDNAmDNA

Fetus inherits mDNA only Fetus inherits mDNA only from ovumfrom ovum

Number of mDNA mutations Number of mDNA mutations indicates antiquity of speciesindicates antiquity of species

Out of Africa: ProceduresOut of Africa: Procedures

Rebecca Cann and colleagues: Rebecca Cann and colleagues: Sampled 147 womenSampled 147 women

mDNA shows little diversitymDNA shows little diversity Sample was to be worldwideSample was to be worldwide

Africans should show the most mutationsAfricans should show the most mutations New Guinea (NG)/Australian, dated 80K BP, includedNew Guinea (NG)/Australian, dated 80K BP, included Africans showed 3 times mutation of NG./AustraliansAfricans showed 3 times mutation of NG./Australians Other populations similarly sampledOther populations similarly sampled

Results tended to support claimResults tended to support claim Mutations traceable to a single African femaleMutations traceable to a single African female Hence, “Mitochondral EveHence, “Mitochondral Eve

Out of Africa: mDNA a Out of Africa: mDNA a flawed methodologyflawed methodology

Nature of the flawsNature of the flaws Sample was too small: 147 out of 2 billionSample was too small: 147 out of 2 billion All “African” women were AmericanAll “African” women were American

Potential admixture with Europeans, Native Potential admixture with Europeans, Native Americans, and AsiansAmericans, and Asians

Order of data input influenced resultsOrder of data input influenced results Alan Templeton reran the testsAlan Templeton reran the tests

Found mutation rates equal for Africans, Found mutation rates equal for Africans, Europeans, and AsianEuropeans, and Asian

Supports mulitregional theorySupports mulitregional theory

Out of Africa Theory: Out of Africa Theory: Retests of mDNARetests of mDNA

Laurence Excoffier & Andre LanganayLaurence Excoffier & Andre Langanay Tested larger sampleTested larger sample

Africans from Africa exhibited less diversityAfricans from Africa exhibited less diversity Than European and Asians.Than European and Asians.

Cann and colleagues ran a retestCann and colleagues ran a retest Sample much larger--5,000Sample much larger--5,000 Africans from African includedAfricans from African included Support more modestSupport more modest

Africans showed more diversityAfricans showed more diversity But the variations were not statistically But the variations were not statistically

significantsignificant

Mitochondrial DNA: Mitochondrial DNA: General Results, If AnyGeneral Results, If Any

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

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

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

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

For full argumentation, see pp. 331-344.For full argumentation, see pp. 331-344.

ConclusionConclusion Fragmentary data makes the controversy Fragmentary data makes the controversy

less than conclusive.less than conclusive. It depends on our typology, from It depends on our typology, from

Tattersall’s extreme splitter taxonomy to Tattersall’s extreme splitter taxonomy to Wolpoff’s lumper’s imagination. Wolpoff’s lumper’s imagination.

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

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

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