Anthropology Exam Questions (Required ASAP)

Lecture #19—Origin and Dispersal of Homo sapiens

Hominins c.200,000ya

Homo neanderthalensis

Homo heidelbergensis

Homo heidelbergensis

Late persisting Homo erectus?

Denisovans????

Right before Homo sapiens

• Homo heidelbergensis, or other premodern humans, in Africa and Asia

• Homo neanderthalensis in Europe and Western Asia

• Possibly late persisting Homo erectus populations in South East Asian Islands

• Maybe the Denisovans or their precursors in Siberia??????

Take note of time, distribution, and how different species are connected to each other.

How do modern Homo sapiens emerge from this picture?

• Traditionally, there were two main models (AE 26, 27 very helpful): – Out of Africa or Complete Replacement Model

– Multiregional or Regional Continuity Model

• Today, a different model has emerged that fits the most recent, best evidence better than OOA or MR: – The Mostly Out of Africa or Partial Replacement or

Leakey Replacement Model

Do we remember what a model is?

• We can think about this as being like a theory.

• A model is a conceptual representation of some phenomenon, a generalized framework that makes sense of facts.

– The phenomenon we are trying to explain is the origin and dispersal of Homo sapiens, i.e. the appearance of modern humans in the fossil record about ~150-200kya and their settlement of Afro- Eurasia and, later, North and South America.

Phenomenon = Origin and Dispersal of Modern Homo sapiens

• In this case, the facts are the distribution of fossil remains of different human species throughout Africa, Asia, and Europe, as well as new genetic evidence comparing Homo sapiens to Homo neanderthalensis and genetic evidence comparing modern, living Homo sapiens from different populations to each other.

Phenomenon = Origin and Dispersal of Modern Homo sapiens

• So, given the evidence we have—fossils and genetics—how can explain the origin and dispersal of modern humans?

• Which model is most consistent with the facts?

• Let’s see what our competing models argue…

From the original publication of Gibbons (AE 26 in Science)

Multiregional Continuity

Beginning with H. erectus leaving Africa, many populations of hominins throughout the Old World were in genetic contact with their neighbors, exchanging members and mates. This maintained gene flow between human populations across the entire range, from Africa to Europe and Asia.

Multiregional Continuity, cont.

Thus, evolution of these groups into modern humans occurred simultaneously across the Old World range, with genetic contributions coming from all regions, not just Africa. In this version, all humans starting 2 mya are members of the same species, with variants being distinguished at the subspecies level (Homo sapiens neanderthalensis vs. Homo sapiens sapiens). •

Multiregional Continuity, cont.

Differences between populations in Africa, Asia, and Europe are thought to be adaptations to regional climate differences. There is continuity over time in these features in each region, and these are ultimately the foundation of modern human variation between these three main regions. •

Out of Africa

While various premodern populations existed across the Old World, by 150-200 kya, anatomically modern Homo sapiens arose in a small area of Africa. This initial population spread throughout Africa and then across the entire Old World. Premodern populations were replaced by the moderns, either through indirect competition, warfare, or disease. No interbreeding occurred between the different species.

Leakey Replacement

This model is essentially the same as Out of Africa but allows for some interbreeding between moderns and some premodern populations they may have encountered. This allows for some contribution to the original modern human genome from outside Africa, and also subscribes to the one species model beginning with H. erectus (have to account for ability to interbreed).

A Note about Fossil Species

• Biological species concept (from many weeks ago)—a species is a group of organisms that are reproductively isolated from other such groups. That is, it a group of organisms that can only reproduce, and produce fertile offspring, with each other.

• This works pretty well when you are dealing with living species you can observe but what about fossils?

A Note about Fossil Species

• If there was interbreeding between modern and premodern humans (Homo heidelbergensis, Homo neanderthalensis, or the Denisovans), then, according to the biological species concept, all 4 of those populations of humans would be the same species.

• But the case can be made that it is still useful to separate them into separate species in order to delineate between the different populations, times, and characteristics that describe them.

• See the box on p. 130 of AE for some discussion of this.

We have our models, now what?

• Now our task to examine the evidence and see which model is most consistent with what we actually see.

• As we go through the evidence, keep this question in your mind: – If <insert name of model here> is correct, what

would we expect?

– E.g. If Out of Africa is correct, where would we expect to find the oldest fossils of modern Homo sapiens?

We have our models, now what?

• Hopefully, you said Africa. If Out of Africa is correct, we would expect to find the oldest fossils of modern humans in Africa. – But, if Leakey Replacement is correct, we would also

expect to find the oldest fossils of modern humans in Africa.

– If Multiregional Continuity is correct, though, we might expect the oldest fossils to be just about anywhere in the Old World or to find contemporaneous modern human fossils in several regions.

• So, where are the oldest fossils of modern humans found?

Oldest Fossils of Modern Humans

• Omo Kibish, Ethiopia

– 190kya

• Herto, Ethiopia

– 154-160kya

• South Africa

– Border Cave

– Klaises River Mouth

– 80-120kya

Oldest Fossils of Modern Humans

• Omo Kibish, Ethiopia—195kya; distinct chin, large cranial capacity

• Herto, Ethiopia—160-154kya – modern brain size 1450cc and non-prognathic face but

more robust – classified as “near modern” by discoverers, who

suggest a sub-species designation Homo sapiens idaltu (elder in Afar language)

• Border Cave and Klaises River Mouth – 80-120kya—very old but some contemporaneous

finds just outside of Africa in Israel

What can we conclude at this point?

• The evidence is consistent with both Out of Africa and Leakey Replacement.

• Good news for these two models but this evidence is not enough to help us differentiate between the models.

• The evidence is inconsistent with Multiregional Continuity.

• Where are the first fossils of modern humans outside of Africa?

– Where might each model predict we find them?

Oldest Out of Africa—Near East

• Skhul Cave, Israel

– 100-130kya

• Qafzeh Cave, Israel

– 92-120kya

Oldest Out of Africa

• On the doorstep in the Near East.

• Skhul Cave (near Tabun, Neanderthal site)

– 100-130kya; some more robust than others, at least 10 individuals

• Qafzeh Cave

– 92-120kya

– some more robust than others, at least 20 individuals

Models?

• Consistent with Leakey Replacement—oldest humans outside of Africa are right outside of Africa but show some premodern traits.

• Not necessarily inconsistent w/OOA, depending on interpretation of the more robust features but interbreeding is possible, which would be inconsistent with OOA.

• BUT definitely inconsistent with Multiregional Continuity since they predate Neanderthal occupation of the region.

Oldest in Asia

• China – Tianyuan Cave

• 40kya

– Zhoukoudian Cave • 27kya

– Ordos • ~40kya?

– Jinnushan?

• Indonesia – Niah

• 40-45kya

Earliest Moderns in Asia

• China – Tianyuan Cave—mandible image; plus post-cranial,

suggesting some archaic characteristics, possible evidence of interbreeding with H. heidelbergensis? still open but earliest evidence of moderns in Asia • 40kya

– Zhoukoudian Cave—cranium in white • 27kya

– Ordos • ~40kya?

• Indonesia – Niah—profile on black; very modern

• 40-45kya

Models?

• The earliest moderns in China do not resemble modern East Asian populations living today but rather share more similarities with the early European sites of Mladec and Premosti. – This strongly suggests a common origin for the

European and Asian fossils, contradicting the predictions of MR.

– Migrated out of Africa before splitting into European and Asian populations.

• Best fit is Leakey Replacement. •

Australia

• Lake Mungo

– 55kya

• Kow Swamp

– 9-14kya

Australia

• Lake Mungo

– 55kya; although some debate—archaeological remains dated to 25-30kya but new electron spin resonance dates for skeletal remains, as old as 60kya

• Kow Swamp

– 9-14kya but very robust crania; hard to know how these fit in since the post-cranial anatomy matches moderns AND recent genetic analysis demonstrate all aboriginal Australians descended from a single migration 50kya

Models?

• Consistent with Leakey Replacement

Central Europe

• Oase Cave, Romania

– 35kya

• Czech Republic

– Mladeĉ—31kya

– Dolní Věstonice—26kya

Central Europe

• Oase Cave, Romania

– 35kya—robust but consistent with later specimens, clear chin

• Czech Republic

– Mladeĉ—31kya; some with more robust brow ridge but modern

– Dolní Věstonice—26kya

Models?

• Consistent with Leakey Replacement

Western Europe

• Cro-Magnon, France

– 28kya

• Lagar Velho, Portugal

– 24.5kya

– 4yo child

Western Europe

• Cro-Magnon, France – 28kya – relatively thin, longer limbs characteristic of recent tropical

origins

• Lagar Velho, Portugal – 24.5kya – 4yo child—shows some affinities with Neanderthals, lack

of chin, limb proportions, and muscle attachments – “the presence of such admixture suggests the hypothesis

of variable admixture between early modern humans dispersing into Europe and local Neanderthal populations” (Duarte et al. qtd in Jurmain et al., 2011, p. 291)

Models?

• “the presence of such admixture suggests the hypothesis of variable admixture between early modern humans dispersing into Europe and local Neanderthal populations”

• Leakey Replacement is BEST FIT.

Where do we stand with the fossil evidence?

• The fossil evidence appears to support Leakey Replacement more than the other two models, although fossil evidence is, by its very nature, indirect evidence. – That is, no matter how smart we are we cannot

conclusively state that the remains of any one individual are the result of interbreeding between two different species of human.

• Is there any evidence we can look at that might be more conclusive, i.e. direct?

Genetic Evidence

• Mitochondrial DNA (mtDNA)

• Y-chromosome DNA

• Ancient DNA

• Remember the molecular clock from the Becoming Human films? That is what we are talking about here.

Genetic Evidence

• Analysis of DNA from different human populations and from Neanderthals can help resolve the debate between these models.

• Some basics about the genetic evidence and DNA comparisons: – Known mutation rate—can compare variation in mutations

between populations to see which are older and which are newer (molecular clock discussed in BH).

– Older populations will tend to have the most variation, while younger populations will have less.

•

Genetic Evidence

• Genetic drift explains this. Groups that split off and migrate will have a more homogenous gene pool to start with than the larger population they are leaving.

– Older populations will have a longer time to accumulate more varieties of mutations and will thus show more variable DNA than newer populations.

Genetic Evidence

• We can compare patterns of DNA variation between living populations (and now some fossils, too!) to determine which have been around longest, which are more recent offshoots.

• We can use level of variation and known mutation rate to assess time depth of splits and can say where the last common ancestor group of all humans lived (LCA).

Mitochondrial DNA

LCA

Mitochondrial DNA

• Small organelles in your cells that have their own DNA that is separate from the DNA that actually runs your body. All mtDNA is inherited from your mother.

• Worldwide study of mtDNA variation found the greatest degree of variation in Africa.

• LCA dated to 180kya in Africa

• In mtDNA, there are very old lineages that are found only in Africa but also find other African lineages represented in younger groups outside of Africa

• Consistent with Leakey Replacement (and Out of Africa)

Y-chromosome DNA

Y-Chromosome DNA

• Only passed down through male side, only males carry Y- chromosome (everyone has mtDNA).

• Comparative study of Y-chromosome: – LCA in Africa as long ago as 142kya but probably more recently

~90kya. – Deepest lineages found only in Africa, indicating the longest

period of evolution took place in Africa, with side branches migrating to other areas and starting new lineages.

• ONLY tracing DNA on Y-chromosome (or mtDNA), not the origins of the entire genome; different genes will have different genealogies

• Consistent with Leakey Replacement (but not inconsistent with OOA)

Ancient DNA until May 7, 2010

Svante Pääbo, Max Planc Institute for Evolutionary Anthropology

Ancient DNA

• Comparative study of DNA from 8 Neanderthals and 7 early modern European humans – Neanderthals fall outside the range of variation seen in modern

humans and form their own cluster separate from humans – LCA estimates between moderns and Neanderthals dated to

365-853kya • Probably Homo heidelbergensis!!!!!!

– LCA of all Neanderthals is estimated 151-352kya

• Modern fossil human DNA is much more similar to living moderns than it is to Neanderthals

• These results tend to support Leakey Replacement but are not inconsistent with OOA.

•

The Neanderthal Genome

The Neanderthal Genome

• The first study Pääbo and his colleagues did was with an incomplete Neanderthal genome. Just a couple of years later, they were able to sequence more of the Neanderthal genome and did a new study.

The Neanderthal Genome

• From Science 5/7/10: “Analysis of the Neanderthal genome indicates that, contrary to previous beliefs, humans and Neanderthals interbred. The first genome sequenced from an extinct human relative is now available. Together with an international research team, researchers at the Max Planck Institute for Evolutionary Anthropology in Leipzig present an initial draft of the genome sequence of the Neanderthal, a human form which died out some 30,000 years ago. Initial analyses of four billion base pairs of Neanderthal DNA indicate that Neanderthals left their mark in the genomes of some modern humans.”

The Neanderthal Genome

• Genetic material from several Neanderthal bones in Croatia, Russia, Spain, and the original German specimen has allowed researchers to reconstruct over 60% of the Neanderthal genome. – Modern humans and Neanderthals share about 99.7%

of their genes

– According to the paper, between 1-4% of that .3% difference in some modern humans living today originate from the Neanderthal:“Those of us who live outside Africa carry a little Neanderthal DNA in us,” Pääbo.

The Neanderthal Genome

• The Neanderthal remains were compared to living humans of African, Asian, and European origin.

• The Neanderthals were slightly more closely related to the non-Africans than to the Africans but showed no difference in relatedness between the Europeans and Asians.

The Neanderthal Genome

• “Neanderthals probably mixed with early modern humans before Homo sapiens split into different groups in Europe and Asia,” Pääbo.

– This likely occurred in the Near East (the Middle East) around 50-100kya, consistent with the fossil record showing overlapping occupation of the region of moderns and Neanderthals.

Current Best Explanation

Current Best Explanation

• While there was definitely some admixture between moderns and Neanderthals, the populations that started migrating Out of Africa 50-100kya spread out to populate the rest of the world (as demonstrated by the similarity of the non-African living humans) and experienced selection pressures that led to most of the Neanderthal DNA being selected against. – The majority of the modern human genome has African

origins but non-Africans have a little Neanderthal tossed in – It looks like some of those Neanderthal genes might be

related to immune system, which makes sense since Neanderthals would have adapted to pathogens in their areas, making those genes advantageous

Peopling the World

Expansion out of the Old World

Archaeological Sites

• Cactus Hill, VA: 11 kya, maybe 15-17 kya

• Schaefer and hebior, WI: 12-14 kya

• Topper, SC and Meadowcroft, PA: at least 12 kya, maybe as old as 20 kya???

• Paisley, Oregon: 14 kya

• Monte Verde, Chile: 14 kya

Skeletal Remains

• Lapa Vermelho, Brazil: 12 kya

• Warm Mineral Springs, FL: 10 kya

• La Jolla, CA: 10 kya

• Browns Valley, MN: 9 kya

• Kennewick, WA: 8 kya

Early Modern Human Social Life

• Foragers

– Foraged foods

– Hunted game

• Small bands—extended families

– Migration between groups for mating

– Cooperative rearing of young

• Modern foraging populations as model for early humans

__MACOSX/Anthro Lectures/._Lecture 19 Origin and Dispersal of Homo sapiens.pdf