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Human. Evolution. What were our ancestors like?. Where did we evolve? Why big brains? Relationships between populations?. Mammalian traits and implications for humans Large brain for body size, for vertebrates Placentation, internal gestation Lactation

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human

Human

Evolution

What were our ancestors like?

Where did we evolve? Why big brains?

Relationships between populations?

slide2

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-> what has evolved forms substrates for what becomes maladapted

mitochondrial gene phylogeny
Mitochondrial gene phylogeny

Very short branch; for

some genes we are closer

to Gorilla

slide7

Humans (we) are a species of chimpanzee

~6 million

years, based on

fossils and molecular clocks

Hominids or hominins

Humans

Chimpanzees

slide8

Comparing chimp and human traits

Species 1Species 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

within the human lineage protein coding genes
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

relationships among contemporary humans mitochondrial dna
Relationships among contemporary humans: mitochondrial DNA

Europe, Asia, Australia

See the

bootstraps?

Asian / Australian

African

See the outgroup?

slide11

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

slide13
Humans are a recently-evolved species, and human genetic diversity is very low compared to other apes
human genetic diversity is distributed mainly within populations
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

fossil data fits with dna data
Fossil data fits with DNA data

Found only in Africa

Found both in Africa and outside, or only outside Africa

do we share genes with neanderthals or homo erectus
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!

origins of modern humans
Anatomically modern humans in Africa ~130 KYA

In Israel by ~90 KYA

Not enormously successful

Origins of modern humans

Omo I, Ethiopia, ~130 KYA

origins of modern humans1
Modern human behaviourstarts to develop in Africa after ~80 KYA

By ~50 KYA, features such as complex tools and long-distance trading are established in Africa

Origins of modern humans

The first art? Inscribed ochre, South Africa, ~77 KYA

slide27

The Human Brain: It’s 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’

slide29

Big brains and small guts

Better

food;

Cooking

of food

slide33

Evolution of this suite of characters human and chimp lineages

Upright before big brains; teeth smaller

slide34

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

slide35

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)

->effects on demograpy

->mother-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

slide36

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

slide37

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, Parkinson’s

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->

negative effects

Pubertal growth spurt Osteosarcoma

Menopause Premature ovarian failure

slide38

RELATING HUMAN MOLECULAR EVOLUTION TO HUMAN DISEASE

Genes subjet to recent positive selection in humans are involved in neurological diseases

Crespi 2010, Evol. Appl.