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Human Evolution (Humans (Why do only Homo sapiens exist? (Symbolic thought…
Human Evolution
Humans
Why do only Homo sapiens exist?
First to make projectile weapons
Symbolic thought
Suggested by having art
Larger brain
Ultrasocial
Learning by observation
Language
Migration from Africa
Homo erectus
1.9MYA
Neanderthals
400KYA
Homo sapiens
60KYA
Genetics
93%-95% of human variation is within populations
5-8% of variation due to between population differences
Most genetic variation in Africa
Caused by bottlenecks during migration
Evidence of one gradual expansion with serial bottlenecks
Demographics
Y chromosomes, but not DNA
Bottleneck around 10KYA
Variation of male reproductive success
Introduction of agriculture
Evolution of technology
Natural selection
Genomic evidence
Selective pressures
Infectious diseases
Sperm selection
Poisonous foods
Diet
Information processing
Ongoing selection
Only 22% of conceptions end in live birth
Maternal system for detecting embryo abnormalities
Directional selection
Earlier fertility
Delayed menopause
Longer male lifespan
Shorter women
Taller men
Lower cholesterol
Lower female B.P.
Evolution of Human Features
Coincided with spread of savanna in Africa
Bipedal Locomotion
Long legs
Loss of opposable big toe
Pelvis & skull changes
Hands no longer needed to walk
Carrying stuff
Neoteny
Loss of hair
Bigger head, brain, eyes, flat face, reduction in brow ridge
Lack of penis bone
Presence of hymen
Short limb:torso ratio
Reproduction
Can get pregnant while caring for young
Increased population growth rate
Closest Living Relatives
Chimpanzees
<2% difference in protein coding DNA
Bonobos
Much less conflict than chimps
Females have higher social rank
All kinds of sex
Gorillas
least related
Hominins
Earliest hominins
Small cranial capacity
Some capacity for upright walking
Archaic hominins
Several species existed at same time
Full upright walking
Stone tools (3.4MYA)
The Genus Homo
Features
Bigger brains
Longer legs
Abundant tool use
Fire to cook food
Extracts more calories
Smaller jaws and mouths
Smaller abdomen
Increased female body mass
Increased brain size
Originated 2.3MYA
Species
Homo floresienis
"Hobbits"
3.5" tall and 55lbs
Insular dwarfism
Went extinct ~50KYA
When sapiens arrived
Indonesian island of Flores
Homo naledi
Discovered in 2015
1.5m tall and 45kg
Related species not clear
Dated bones to 236-335KYA
Features
Brain size ~Australopithecus
Dextrous hands
Feet for upright walking
Reduced jaws and teeth
Neanderthals
Extinct ~40KYA
Features
11% bigger brains
Sophisticated tools and fire
Hunted large game
Cared for sick and elderly
Probably had language
Buried dead
Denisovans
More closely related to Neanderthals than sapiens
More widespread than Neanderthals
3% of DNA of Melanesians and Aboriginals
Interbred with Neanderthals (17% DNA)
Little known about them
3 teeth and finger bone found
Finger bone is larger than sapiens
Evolutionary Roots
Many aspects shared by animal kin
Fear
Generated in amydala (100MYA)
Survival adaptation
Motivation
Depends on dopamine
Love
Oxytocin or vassopressin
Sex and Death