Human Evolution What were our ancestors like Where

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 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

Who are the closest living relatives of humans? How do we know? Bonobo Chimp Gorilla Orang

Early evidence from immunology

Mitochondrial gene phylogeny Very short branch; for some genes we are closer to Gorilla

Humans (we) are a species of chimpanzee ~6 million years, based on fossils and molecular clocks Hominids or hominins Chimpanzees Humans

Comparing chimp and human traits Species 1 Species 2 Hug, kiss, back-pat, hold hands Use tools and medicines Use gestural, vocal communication Dominance, status among males Male friendships and kin bonds Female & female-male friendships Territorial, have warfare Eat fruit, vegetables, meat, primates Large groups, fluid subgroups 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 Based on 120 protein-coding genes in 1, 915 populations Cavalli-Sforza & Feldman (2003) Nature Genet. 33, 266 -275

Europe, Asia, Australia See the bootstraps? Relationships among contemporary humans: mitochondrial DNA Asian / Australian African See the outgroup?

Mitochondrial EVE - simplified example Among all humans, 0. 4% difference in mt. DNA, basal lineages on tree are all African (tested as hypothesis) Among group of humans isolated for 50 K 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 to modern humans mt. DNA WHAT THIS DOES NOT MEAN: one female alive then, or we all have same mt. DNA, or Eve was anatomically or behaviorally modern

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 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 Found only in Africa Found both in Africa and outside, or only outside Africa

Recent human phylogeny (best guess)

Do we share genes with Neanderthals or Homo erectus? Some apparent gene flow here? mt. DNA, 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 Omo I, Ethiopia, ~130 KYA

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

‘Multiregional’ vs ‘replacement’ models for origin of modern humans

RESULTS UNCLEAR, DISPUTED

Bottleneck!

Tripled!

The Human Brain: It’s not just bigger (1) Increased anatomical and functional lateralization (left hemisphere ‘for’ language, right hemisphere ‘for’ emotion, visual-spatial tasks) (2) Increased proportion of fat (DHA, AA) (3) Disproportionate expansion of heteromodal association cortex (the thinking parts), cerebellum, some other areas (4) Expansion and elaboration of the ‘social brain’

Sizes of mammalian, primate, Hominoid, and human brains

Big brains and small guts Better food; Cooking of food

Evolution of this suite of characters human and chimp lineages Upright before big brains; teeth smaller

The stages of human preadult development, including transition landmarks and endocrine factors mediating growth and development at different stages. IGF 2 also strongly mediates prenatal growth. Adapted from Bogin (1994, 1997, 2006) and Hochberg (2010). From Crespi 2011; Evolution of Child Health, PRSLB

Evolution of human life stages (1) Emerge as fat fetus, physically altricial but neurologically advanced; ‘displays’ of health, vigor? (analogous to h. CG) (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 (1) (5) Long adult lifespan, with post-reproductive (2) period in females, substantial generation (3) overlap in extended family networks

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

RELATING HUMAN PHENOTYPIC EVOLUTION TO HUMAN DISEASE Human-evolved adaptation Human disease/disorder with losses of function Large brain Social brain High intelligence Language Expansion of dopaminergic system Microcephaly Autism Intellectual disability Specific Language Impairment Schizophrenia, Parkinson’s Low conception rate/cycle Deep placental invasion, spiral arteries modified Fat babies Infertility Pre-eclampsia Early weaning Long preadult stages Attachment disorders Early adrenarche, puberty-> negative effects Osteosarcoma Premature ovarian failure Pubertal growth spurt Menopause Intrauterine growth restriction

RELATING HUMAN MOLECULAR EVOLUTION TO HUMAN DISEASE Genes subjet to recent positive selection in humans are involved in neurological diseases Crespi 2010, Evol. Appl.