Human Evolution - Lecture Notes (Spring 2019) PDF

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Human Evolution Lecture Notes. The professors for this course were Dr. Sam Brown and Dr. Soojin Yi....

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Lecture 21

4/4/19 Human Evolution

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Learning Catalytics Q: Based on what you have seen so far, which trait has evolved earlier than the other? o Bipedalism Learning Catalytics Q: What would be the best clue that a fossil skull was left behind by an ape that walked more or less upright? o The foramen magnum has a position relatively far forward. Learning Catalytics Q. Which genera is likely the most recent ancestor of the genus Homo? o Australopithecus Humans are hominins o Hominins = species in lineage leading to modern humans Archaic Humans o Neanderthals & Denisovans o H. floresiensis Modern Humans o H. sapiens Human Lineage Traits o Bipedalism: most defining characteristics of hominin lineage  Walking/running  Associated w/:  Pelvis shape  Leg length & angle  Position of connection b/w skull & spine (aka foramen magnum) shifted forward so we can face straight when standing  Unique foot anatomy  Loss of body hair may be consequence to this to create sweating o Skeletal anatomy  Shorter arms to legs ratio than apes  Hand anatomy (our fingers are shorter/straighter & thumbs are more opposable than apes’) o Cranial/jaw anatomy  Flat face, small teeth o Big brains  Progressive changes throughout hominin evolution o Language  Likely shared by modern & archaic humans Common traits b/w humans & apes o Opposable thumbs o Highly social o Use tools for learning o Theory of mind o Communicate w/ humans Hominins

Lecture 21

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o Small teeth o Flatter face o Small brain case o Small brain o Opposable big toe o Pelvis for bipedalism o Lucy fossil shows bipedalism H. erectus & H. habilis likely to been ancestors of modern humans o H. erectus:  Made tools  Used fire  Large brains  1st migration ‘out of Africa’ Human Brain: prime example of evolutionary innovation o Large brains began to evolve earlier than hominin lineage o Apes have larger brains than other mammals o Brain evolution expedited in recent human evolution Social brain hypothesis: Our brains got bigger b/c we had to adapt to this bigger society & socializing o Especially of neocortex which is responsible for learning, memory, & cognition o Size of brain corresponds to that of species that lived in ‘mean group size’ of 148 o Dunbar’s #: 150 is mean group size for communities w/ high incentive to stay together  Lot of ‘social grooming’ needed to keep group  Applicable to online social networks o Language may have selective advantage as ‘cheaper’ means to offer social grooming  Language evolution accompanied by physiological changes of larynx (disadvantage: easy to choke) 3 waves out of Africa o Substantial: interbreeding b/w archaic humans & anatomically modern humans o 1st wave: Homo erectus (2M years ago)  some went to Europe & evolved  rise to H. floresiensis o 2nd: Ancestors of Neanderthals & Denisovans (600,000 years ago) o 3rd: migration of modern humans

Lecture 21

4/4/19

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more variability in African populations

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Non-African populations = Decreased heterozygosity & Increased linkage disequilibrium

Learning Catalytics Q: Which piece of evidence does not support the theory of recent (200,000 years ago) African origin of humans? Mitochondrial DNA sequences coalesce to Africa popula6ons about 125,000 years ago. o Linkage disequilibrium of nuclear genes gets progressively lower as one measures popula6ons farther from Africa. (B/C IT HIGHER NOT LOWER) o Haplotype diversity of nuclear genes is greatest in Africa. o Fossils of modern humans older than 60,000 years are found only in Africa. o Non-African populations show reduced heterozygosity compared to African populations. 

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Contiguous introgression b/w modern & archaic humans o Neanderthal ancestry found in non-African populations o Denisovan ancestry found in Melanesians o Neanderthal-Denisovan interbreeding also observed Brain, metabolism, cooking, agriculture o Human brain uses 20% of metabolites o Humans have higher metabolic rates than other apes o Hypothesized that high metabolic rate of humans achieved by evolutionary shift of diet (from fruits to meat/tubers) o Evolution of agriculture changed history  Foundation for human civilization  Sedentary life  Increase of population size  Habitat destruction & species extinction

Lecture 21

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