ANTH151 Lecture Notes - Lecture 5: Paranthropus, White Matter, Evolution Of The Brain
10 May 2018
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ANTH151 Lecture
V: Brains: What are they good for?
How did evolution produce such an unusual brain?
• Encephalization
• Developmental dynamics
Why have a brain?
• Tunicates or ‘sea squirt’
• Adult possesses no ‘brain’ or neutron cluster; immature larva does
• Once immobilised and a passive feeder, the need for the brain is no longer present
Simple brains
• With simple brains, stimuli response are closely linked
• A stimulus ‘releases’ or provokes a stereotyped response (recoiling from pain, moving
towards food, presence of rival provokes threat display)
Humans?
• Disgust responses to certain smells
• Some facial expressions
• Sexual arousal
• Pain response
• Stress response (fight or flight)
• The responses themselves may be stereotypical and universal, but cuing them can be a wide
range of stimuli
More complex brain, less automatic and stereotypical responses
• Although ‘triune brain’ idea is misleading, the layered emergence (both in evolution and
development) means that slow-growing, large brains have more overlaying control and
variation
Encephalisation
• Evolutionary trends
• Encephalisation Quotient (EQ)
Homo habilis
• Habilis because of handy man
• Discovered 1960
• Remains 2.3 - 1.6 mya
• Overlaps Australopithecenes and Paranthropus
• Skeletal traits variable
• May have made stone tools
Homo ergaster
• Work man
• Discover 1976
• 1.8 to 0.6 mya
• Larger body than earlier hominins with modern proportions (savanna populations)
• Human-like trains
• Left Africa for Eurasia
• Diet include meat
• Tool use
Comparative neurology
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• Human brain not simply quantitatively different (bigger)
• Qualitative differences are crucial
• Terrence Deacon: searching for special ‘language’ part of human brain
Conserved and derived traits: using similarity and different in brains
• Deep homologies help us to see and understand the deriving of specific variants
• Comparison amongst different orders of mammals and amongst the primates
• Growth of associative cortex
Allometric scaling
• As the brain size increases, not all areas increase equally
• Disproportionate increase of some areas shifts cerebral ‘balance of power’
Brain areas that grew
• Frontal lobe, associated with synthesising information from other areas and inhibiting actions
(‘downward processes’)
• Volume of white matter, brain interconnections, grows faster than neocortex, eventually
constituting 34% of human brain BUT interconnection not proportional: specialisation
• Differentiation or specialisation of tissue (but only through development)
Key concepts
• Neuroplasticity (developmentally-based malleability)
• Displacement (as brain areas grow in relative size, they send out extra connections)
• Cortical specialisation (outer layers less interconnected)
• Executive control (brain internally directed more than externally reactive)
Evolutionary psychology
• Human abilities are innate and ‘domain specific’ (highly specialised)
• ‘Stone age’ mind in Space Age world because evolution slow (culture and technology fast)
• Humans today are a good proxy for our ancestors (because mind is innate)
• Examples
• Learning language
• Social bonding
• Choosing a mate
• Reading each other’s emotions
• Social ‘cheater’ detection
• Fearing predators
Problems with evolutionary psychology
• Are we sure trait is universal and innate? (Often easier explanation)
• Plausible mechanism to create the trait innately?
• Is the account of evolution accurate?
• Is the trait real an adaptation? Any way to test?
• Exaptation: virtually every structure in the brain has homologues, with wide variety of other
functions
• Heritability: is behaviour really heritable? Behavioural genetics is quite subtle and emerging
science
• Adaptationism: is every trait an adaptation?
• Inconsistent with how the brain develops
Brain development
• Neural Darwinism: neutrons fight for resources
• Less development by ‘blueprint’ than emergence over time
• Makes brains very resilient but also creates really weird possibilities
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find more resources at oneclass.com
Significance
• Distinct human traits can be created by shifting developmental trajectory, tweaking
connection pattern and relative strength of brain areas
• Humans have especially versatile, environment-reactive brain
• Wrong to think of one part of brain as ‘primitive:’ all are evolving, even when balance of
power shifts
How Diet Affects the Brain: Evolution and Development
Nikolaas ‘Niko’ Tinbergen
• Whenever we ask the origin of a trait in evolution, we really could be asking one of four
different questions
• Causation (mechanism): what is the neural mechanism for the function?
• Development (ontogeny): how does that function arise as the organism matures?
• Evolution (phylogeny): when and how did the mechanism emerge over time?
• Function (adaptation): what purpose or adaptive function does a trait serve?
Social brain hypothesis
• Average group size correlates with the ratio of neocortex to the rest of the brain
Skill acquisition hypothesis
• Increased brain diversity and train ability create possibility of greater procedural knowledge
and sophistication
• Tracking, throwing, tool-making, complex foraging, scenario-building
• Ironically, a ‘brainier’ hominid might also have been more physically capable (although
through training, not innate capacity)
Growing a big brain
How did our brains get this way?
• Neoteny: retention of infantile characteristics into maturity
• Homo sapiens has juvenile flat face (compared to chimps) and extended child-like brain
growth
• At birth, we have the same brain-body weight ratio as other Great Apes (by adulthood, 3.5
times more)
Neotony in the brain
• Most mammal brains are fully formed at birth, primates are odd
• Macaques reach 65% of final cranial capacity when born
• Chimps reach 40% of final size
• Fossil australopithecenes range from 37% to 25% of final cranium size at birth
• Humans reach 23% of final cranial capacity before birth
• Theorists have argued that we are extra-uterine foetuses until 21 months
Ecological dominance - social competition
• Flynn and colleagues argue that once humans dominate environment, internal competition
drives evolution. Autocatalytic (self-reinforcing dynamic)
• Intense directional selection for greater social intelligence. Both domain specific and general
intelligence
• Scenario building increased learning and strategic thought
Is intelligence all ‘in the brain’?
• Human intellectual abilities are not carried entirely by genes
• Human company influences intellect
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find more resources at oneclass.com
Document Summary
How did evolution produce such an unusual brain: encephalization, developmental dynamics. Why have a brain: tunicates or sea squirt", adult possesses no brain" or neutron cluster; immature larva does, once immobilised and a passive feeder, the need for the brain is no longer present. Simple brains: with simple brains, stimuli response are closely linked, a stimulus releases" or provokes a stereotyped response (recoiling from pain, moving towards food, presence of rival provokes threat display) Humans: disgust responses to certain smells, some facial expressions, sexual arousal, pain response, stress response (fight or flight, the responses themselves may be stereotypical and universal, but cuing them can be a wide range of stimuli. More complex brain, less automatic and stereotypical responses: although triune brain" idea is misleading, the layered emergence (both in evolution and development) means that slow-growing, large brains have more overlaying control and variation.
