L35 Origin of Modern Humans

Question 1

OOA/E model

Answer 1

• postulates migration/migrations from Africa into Eurasia and elsewhere
• uncertainty in both archaeological and molecular estimations

Question 2

OOA/E model - archaeological evidence

Answer 2

• dating relies of artefacts found at different locations but there is dispute as to whether the earliest ones are those of modern humans or were the word of earlier hominid species such as H.erectus

Question 3

OOA/E model - molecular data

Answer 3

• dates based on time of separation from chimpanzees

Question 4

Simons Genome Diversity

Answer 4

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• investigated 300 genomes from 142 diverse populations, obtaining great range of human diversity
• dating based on coalescence concept
• concluded ancestral population developed about 200,000 years ago
• data consistent with single migration OOA about 50,000 years ago or even an independent origin in Eurasia

however there were modern humans in Eurasia about 100,000 year ago and this dataset cannot provide any answers on how much differentiation might have been present in those populations as there is presently no DNA sequence for any of these remains

Question 5

Reduction in variability in those moving OOA

Answer 5

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• genetic bottleneck prior to migration
• suggested this may have occurred about 200,000 years ago just before the population expansion began

However two papers have presented analyses to show that simple models without bottlenecks are equally able to explain the reduction of genetic variability

• easier of arguments to understand is the point of coalescence
• coalescence will be reached at the same time regardless of whether there is a bottleneck of whether the population maintains a constant size

Question 6

Deviations from OOA

Answer 6

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• cannot be conclusively proven
• there was a migration back into Africa by some of the population known to be in Eurasia before 50,000 years ago
• confirmed by analysis of African genomes, 4,500 year old African male from ethiopia
• comparison of DNA to that of most closely related modern African genomes showed that his lacked about 4-7% of DNA of modern genomes, this DNA therefore came into Africa in the past 4,500 years and estimated as occurring about 3000 ya from Western Eurasia
• supports the idea that it was farmers who migrated back
• subsequently carriers of this DNA migrated to souther Africa and the extent of this DNA throughout Africa suggests that there may have been a large number of the original migrants

Question 7

Other Homo species from which ancient species has been obtained

Answer 7

• successful mtDNA extraction has been achieved back to about 400,000 years ago
• obtaining sequences from traces of DNA in substrate of caves allows determination of which species had used the caves even if no fossil material was present
• archaic Homo may have interbred with modern humans

Question 8

Neanderthals

Answer 8

side branch of human evolution that separated possibly 700,000 ya

disappeared about 30,000 to 40,000 ya

genomes of Neanderthals show more similarity to modern Eurasian populations than they do genome of modern Africans

haplotypes of Neanderthal origin occur in all non-African populations
- suggests there was some hybridisation between Neanderthals and modern humans but that it occurred after Homo sapiens had left Africa

Question 9

Eurasian Genomes

Answer 9

estimated that 1 - 4% of Eurasian genomes comes from Neanderthals but the amount in East Asian Population is 40% higher than in Europe = suggesting a subsequent admixture

Question 10

Neanderthal - East African populations

Answer 10

• signs of neanderthal in some East African populations but this could have arrived with the back-migration of non-African people to East Africa 3000 years ago