The Origins of Modern Humans

1
The Origins of Modern Humans

• Adam Eyre-Walker

2
Human evolution in brief

• Diverged from chimpanzees 5-7 MYA
• Hominids evolved in Africa until 2MYA
• Homo erectus first widely distributed hominid
• Homo sapiens first appears in Africa 150 KYA

3
Two (extreme) models

• Out of Africa
• Modern humans evolved in Africa
• Spread across the globe WITHOUT interbreeding
• Multi-regional
• Archaic humans, distributed across the globe,
  evolved into modern humans

4
Out of Africa - 2MYR
5
Out of Africa - 2MYR to 100 KYA
6
Out of Africa - 2MYA to 100 KYA
7
Out of Africa - 100 KYA
8
Out of Africa - 100 KYA
9
Out of Africa - 50 KYA
10
Multi-regional - 2MYR
11
Multi-regional - 2MYR to present
12
Multi-regional - 2MYR to present
13
Multi-regional - 2MYR to present
14
Multi-regional - 2MYR to present
15
Evidence for Out of Africa

• Fossils
• Oldest human fossils are in Africa
• Genetic diversity
• Greater in Africa
• Non-African diversity a subset of that in Africa
• Origin of diversity is in Africa
• Effective population size too small

16
Modern Human Fossils
17
Evidence for Out of Africa

• Fossils
• Oldest human fossils are in Africa
• Genetic diversity
• Greater in Africa
• Non-African diversity a subset of that in Africa
• Origin of diversity is in Africa
• Effective population size too small

18
High African Diversity
Nucleotide diversity or heterozygosity
19
Out of Africa
20
Out of Africa
21
Out of Africa
22
Multi-regional
23
Multi-regional
24
Conclusion

• Higher diversity in Africa consistent with
• Out of Africa
• Multi-regional
• But only if African population size larger

25
Evidence for Out of Africa

• Fossils
• Oldest human fossils are in Africa
• Genetic diversity
• Greater in Africa
• Non-African diversity a subset of that in Africa
• Root is in Africa
• Effective population size too small

26
mtDNA phylogenetic tree
27
mtDNA phylogenetic tree
28
Y-chromosome tree
29
Autosomal loci

• Takahata et al. (2001) Mol. Biol. Evol.
• 10 loci with resolvable root
• 9 in Africa
• 1 in Asia

30
Out of Africa
Africa
31
Out of Africa
Africa
N
N
32
Multiregional
A
A
N
N
A
N
A
N
A
A
33
Multiregional
Africa
A
A
N
N
A
A
N
N
34
Multiregional root

• Depends on several factors
• Chance
• Population size
• Larger more chance of root
• Migration rate

35
Conclusion

• Out of Africa consistent
• Multi-regional model might be consistent under
  particular circumstances

36
Evidence for Out of Africa

• Fossils
• Oldest human fossils are in Africa
• Genetic diversity
• Greater in Africa
• Non-African diversity a subset of that in Africa
• Root is in Africa
• Effective population size too small

37
Effective population size

• Genetic diversity 4Neu
• Ne is
• the effective population size
• is the population size of random mating
  individuals which would have the same diversity

38
Effective population size
39
Effective population size
40
Ne 10,000

• Reflects long-term population size
• Reflects periods of small population size
• Out of Africa
• Small initial population size
• Multiregional
• Not so consistent

41
Further reading

• Jobling et al. Human Evolutionary Genetics
  Chapter 8