Evolution of the Human Brain • Homo sapiens • Hominin ancestors • Chimpanzees • Primates Evolution of Homo sapiens Origin of anatomically modern humans • ~200,000 ya • Human population genetics • Archeology, Fossil record Origin of anatomically modern humans • Average brain size 1300 cc • Extended life history • Increased post-natal brain growth • Expanded prefrontal cortex relative to early ancestors • Lack of brow ridges, presence of chin • Behavioral flexibility Origins of behavioral modernity • ~70,000 ya • Art, jewelry, stone tool refinement What behaviors are uniquely human? • Language • Abstract thinking • Art • Music • Sociality • Disorders (Schizophrenia, Autism, Alzheimer’s) What neurological changes made us human? • No brain size change 200,000-70,000 ya • Decrease in genetic diversity • Need comparative data for evidence (genetic and fossil) Homo sapiens were not alone Neanderthals, Hobbits and Denisovans Homo neanderthalensis • First hominin fossil discovered, 1856 • 200,000-35,000 ya • Europe, Middle East • Brain size 1420 cc Homo neanderthalensis • Tools, fire • Language? • Art? • Ritual burial Homo floresiensis • 18,000 ya • Flores, Indonesia • Brain 400 cc • Tools ! Denisovans • 40,000 ya • Siberia • Small fossil fragment only Neanderthal brains • Olfaction, vision, reduced prefrontal cortex Hobbit brains (Homo floresiensis) Comparative genomics: Homo sapiens /early hominins • FOXP2 – language • Brain size • Autism • Nerve development Denisovian genes • 8 associated with brain function or nervous system development (NOVA1, SLITRK1, KATNA1, LUZP1, ARHGAP32, ADSL, HTR2B, CNTNAP2). • 4 of these are involved in axonal and dendritic growth (SLITRK1, KATNA1) and synaptic transmission (ARHGAP32, HTR2B) • 2 implicated in autism (ADSL, CNTNAP2). (CNTNAP2 is also associated with susceptibility to language disorders). Hominin brains Taung child (Australopithecus africanus) • Raymond Dart – 1924 • Taung, South Africa • 2.5 mya Human - Chimp comparison Human - Chimp comparison • 1300 cc - 400 cc • Chimp lacks Broca’s and Wernicke’s area • Does have planum temporale – calls are received but not processed as language Human - Chimp comparison “ A small number of genetic changes in the expression of genes may account for the substantial organismal differences between humans and chimpanzees.” Gene expression (epigenetics) Gene expression (epigenetics) Human - Chimp comparison Divergent Whole-Genome Methylation Maps of Human and Chimpanzee Brains Reveal Epigenetic Basis of Human Regulatory Evolution - Zeng et al. Encephalization quotient Evolution of animal models .