The origin of modern humans

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The origin of modern humans Known modern humans
first appear in fossil record c. 190,000 ya in
Africa 115,000 ya in Mideast 60,000 ya Asia
Australia 40,000 ya in Europe
Modern humans?
Two competing hypotheses
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Genetic predications distinguishing STRICTLY
African replacement and multi-regional evolution
models

• 1. Location of ancestor of neutral alleles
• 2. Divergence time of African vs. non-African
  populations
• 3. Genetic diversity
• 4. Sets of neutral alleles

• AR mostly Africa MRE random
• AR 200,000 yr or less MRE 1 mya or greater
• AR greater in Africa MRE approx. equal in all
  regions
• AR European Asian alleles are subsets of
  African alleles
• MRE each region has some unique alleles
• No regions alleles are a subset of those from
  another region

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(No Transcript)
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Predictions from each model
1. the extinct archaic and extant modern humans
in each region will be each others closest
relatives
Lieberman (1995)
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mtDNA All human groups equidistant
from Neandertals Modern human lineage
diverged after it split from lineage leading to
Neandertals Last common mitochondrial ancestor
of Neandertals and modern humans 690-357 ya
352-151 kya
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Did Neandertals have a spoken language?
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Apropos of Dr. Dibbles comments re stone tools
(Neandertals on Trial)
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Predictions from each model
1. all groups of modern humans will be more
closely related to each other than to any archaic
species. 2. among archaic species, those from
Africa will be the most closely related to
modern humans
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Cann, R. L., M. Stoneking, and A. C. Wilson.
1987. Mitochondrial DNA and Human evolution.
Nature 32531-36.
However, this tree summarizes 7.13 x 1035
trees Other trees indicated an Asian origin for
modern human s
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53 individuals complete sequence of mtDNA
Common ancestor of all modern mtDNAs lived in
Africa
B

• Most recent common
• ancestor of all modern mtDNA
• Most recent common
• ancestor of Africans and
• non-Africans

A
Consistent with African Replacement Model
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Comparison of genetic variation (mtDNA)
Chimpanzee subspecies are more genetically
variable than any two human populations
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Phylogeny of 14 populations based on allele
frequenciesat 30 microsatellite loci and genetic
distancesVariable number of tandem repeats

• Geographically neighboring populations cluster
  together
• Basal branch separates African and non-African
  groups
• Split estimated from this data 75,000 to
  287,000 ya
• Consistent with African Replacement Model

Bowcock, Ruiz-Linares, Tomfohrde, Minch, Kidd,
and Cavalli-Sforza (1994)
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• Genetic diversity at a single locus in chromosome
  
• number 12.
• Number of tandem repeats of a DNA sequence
• 12 different alleles
• Among people of 7 geographic regions
• Each plot shows the frequencies of the various
  alleles for people of a particular region.
  Arranged by travel distance.
• If non-African populations were founded by small
  bands of people migrating out of Africa, then
  non-African populations should have reduced
  genetic diversity.
• African populations show much greater allelic
  diversity than non-African populations
• Consistent with African replacement model.

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Competing hypotheses
Paleontological evidence
Milford Wolpoff
Richard Klein
Phillip Rightmire
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Intermediacy between H. heidelbergensis and H.
sapiens Herto, Ethiopia, Africa 160,000 ybp
(argon-argon dating)