Human

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Human
Evolution
What were our ancestors like?
Where did we evolve? Why big brains? Relationship
s between populations?
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Mammalian traits and implications for
humans Large brain for body size, for
vertebrates Placentation, internal
gestation Lactation Primate traits and
implications for humans Large brain for body
size, for mammals Long lifespan Invasive
placentation Live in social groups Excellent
vision, eyes forward (humans, sclera) First
digits opposable (can grasp) Fingernails
(homologous with claws) Origin and evolution of
modern humans represents essential background
for understanding evolution of human genes and
phenotypes related to health and disease-gt what
has evolved forms substrates for what becomes
maladapted
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Who are the closest living relatives of humans?
How do we know?
Chimp
Gorilla
Orang
Bonobo
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Early evidence from immunology
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Mitochondrial gene phylogeny
Very short branch for some genes we are closer
to Gorilla
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Humans (we) are a species of chimpanzee
6 million years, based on fossils and molecular
clocks
Hominids or hominins
Humans
Chimpanzees
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Comparing chimp and human traits Species
1 Species 2 Hug, kiss, back-pat, hold hands
Hug, kiss, back-pat, hold hands Use tools and
medicines Use tools and medicines Use
gestural, vocal communication Use gestural,
vocal communication Dominance, status among
males Dominance, status among males Male
friendships and kin bonds Male friendships and
kin bonds Female female-male friendships
Female female-male friendships Territorial,
have warfare Territorial, have warfare Eat
fruit,vegetables,meat,primates Eat
fruit,vegetables,meat,primates Large groups,
fluid subgroups Large groups, fluid
subgroups Consorts and promiscuity Consorts and
promiscuity IMPLICATION? ALL OF THESE TRAITS
WERE PRESENT IN COMMON ANCESTOR OF CHIMPS AND
HUMANS, ALONG THE HUMAN LINEAGE
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Within the human lineage protein-coding genes
Based on 120 protein-coding genes in 1,915
populations Cavalli-Sforza Feldman (2003)
Nature Genet. 33, 266-275
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Relationships among contemporary humans
mitochondrial DNA
Europe, Asia, Australia
See the bootstraps?
Asian / Australian
African
See the outgroup?
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Mitochondrial EVE - simplified example Among all
humans, 0.4 difference in mtDNA, basal lineages
on tree are all African (tested as
hypothesis) Among group of humans isolated for
50K years, 0.1 different CLOCK CALIBRATION 2
per million years (0.10 div 0.05
million) INFERENCE EVE lived about 200,000 years
ago WHAT THIS MEANS Non-African populations
older than about 200,000 years did
not contribute mtDNA to modern
humans WHAT THIS DOES NOT MEAN one female alive
then, or we all have same mtDNA, or Eve was
anatomically or behaviorally modern
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Humans are a recently-evolved species, and human
genetic diversity is very low compared to other
apes
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Human genetic diversity is distributed mainly
within populations
Most variation between populations
Implication racial differences in humans (in
skin, hair, facial features) are genetically
minor (though there is much evidence for local
adaptation in phenotypic traits)
Most variation within populations
Templeton (1999) Am. J. Anthropol. 100, 632-650
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Fossil data fits with DNA data
Found only in Africa
Found both in Africa and outside, or only outside
Africa
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Recent human phylogeny (best guess)
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Do we share genes with Neanderthals or Homo
erectus?
Some apparent gene flow here?
mtDNA, whole genome from Neanderthals Need
genome from direct human ancestors!
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Origins of modern humans

• Anatomically modern humans in Africa 130 KYA
• In Israel by 90 KYA
• Not enormously successful

Omo I, Ethiopia, 130 KYA
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Origins of modern humans

• Modern human behaviour starts to develop in
  Africa after 80 KYA
• By 50 KYA, features such as complex tools and
  long-distance trading are established in Africa

The first art? Inscribed ochre, South Africa, 77
KYA
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Multiregional vs replacementmodels for
origin of modern humans
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RESULTSUNCLEAR, DISPUTED
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Bottleneck!
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Tripled!
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• The Human Brain Its not just bigger
• Increased anatomical and functional
  lateralization (left hemisphere for language,
  right hemisphere for emotion, visual-spatial
  tasks)
• Increased proportion of fat (DHA, AA)
• Disproportionate expansion of heteromodal
  association cortex (the thinking parts),
  cerebellum, some other areas
• Expansion and elaboration of the social brain

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Sizes of mammalian, primate, Hominoid,and human
brains
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Big brains and small guts
Better food Cooking of food
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Evolution of this suite of characters human and
chimp lineages
Upright before big brains teeth smaller
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The stages of human preadult development,
including transition landmarks and endocrine
factors mediating growth and development at
different stages. IGF2 also strongly mediates
prenatal growth. Adapted from Bogin (1994,
1997, 2006) and Hochberg (2010).
From Crespi 2011 Evolution of Child Health, PRSLB
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• Evolution of human life stages
• Emerge as fat fetus, physically
• altricial but neurologically advanced
• displays of health, vigor? (analogous to hCG)
• (2) Relatively early weaning (6 - 3 years)
• complementary foods early (6 months)
• -gteffects on demograpy
• -gtmother-offspring conflicts
• (3) Spend a LONG time in childhood
• with large brain and small body
• (4) Undergo growth spurt in adolescence
• (5) Long adult lifespan, with post-reproductive
• period in females, substantial generation
• overlap in extended family networks

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Evolution of neoteny (a form of heterochrony) in
humans retain juvenile form into adulthood,
such that human adults are big babies w/regard to
head size, shape
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RELATING HUMAN PHENOTYPIC EVOLUTION TO HUMAN
DISEASE Human-evolved adaptation Human
disease/disorder with losses of
function Large brain Microcephaly Social
brain Autism High intelligence Intellectual
disability Language Specific Language
Impairment Expansion of dopaminergic
system Schizophrenia, Parkinsons Low conception
rate/cycle Infertility Deep placental invasion,
Pre-eclampsia spiral arteries modified Fat
babies Intrauterine growth restriction Early
weaning Attachment disorders Long preadult
stages Early adrenarche, puberty-gt negativ
e effects Pubertal growth spurt Osteosarcoma Men
opause Premature ovarian failure
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RELATING HUMAN MOLECULAR EVOLUTION TO HUMAN
DISEASE
Genes subjet to recent positive selection in
humans are involved in neurological diseases
Crespi 2010, Evol. Appl.