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Chapter 5

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Evolutionary Psychology
• Scientific study of human behaviour, brain,
mind within an evolutionary context
• Relatively new as actual academic
discipline
• Principles have been around for long time
• Not a sub-discipline of psychology, but a
general theoretical approach
Humans’ Place
• Humans are animals
• But are they special animals?
• “Gradual” vs. “recent” development of
modern human characteristics
• Bias, agenda
Mammalian Social Organization
•
•
•
•
•
Milk production
Mother-offspring association
Matrilineal cross-generational bonds
Females are the limiting resource
Polygyny and monogamy
Milestones
major advance in tool
agricultural revolution
manufacture; the
origin of modern humans
first cities (6k)
Mousterian (200k) in Africa (200k?)
Industrial Revolution (150)
first evidence of
art (70k)
controlled use of fire (~800k)
technological revolution (25)
present
evidence of meat eating
becomes strong
0.01 million
0.1 million
grinding wild grains for baking (25k)
1 million
Major advance in tool manufacture; the Achulean
2 million
Homo erectus expands
out of Africa
earliest-known stone tools, Africa
origin of brain expansion
3 million
Adapted from: Leakey (1994)
earliest-known fossils
origin of bipedalism
(A. afarensis Homo sp.?)
in Africa
4 million
5 million
10 million
Australopithecine
Homo habilis
Homo erectus
Homo Neanderthalensis
~ 3.5-2.7 myr
Brain size: 650 cc
~2.4-1.7 myr
Brain size: 800 cc
~1.7-0.3 myr
~250-45 kyr
Brain size: 900 cc Brain size: 1400cc
Image sources: http://www.archaeologyinfo.com, http://paleodirect.com/, http://www.talkorigins.org/faqs/homs/eurydice.jpg
Broad “Assumptions” of EP
• Brain is physical system
• Psychological systems (neuronal, cognitive,
behavioural) adaptively selected for
problems faced by our ancestors in
Environment of Evolutionary Adaptiveness
• Selective pressures have produced cognitive
modularity
Brain is a Physical System
•
•
•
•
Materialism
Brain is a physical organ
Activity of brain is “the mind”
Evolution typically used to study physical
adaptation
• But behaviours derived from brain, so
evolution can be applied here, too
Adaptive Selection
• Environment of Evolutionary Adaptiveness
(EEA)
– Period of evolutionary pressures on human
ancestors prior to about 10000 years ago
• Selected and shaped species-specific traits
seen in modern humans
• Because of changes in environment, some
of these traits may no longer be well suited
to the modern environment
Modularity
• Fodor (1983), The Modularity of Mind
• Small, independent, impenetrable units
• Generally applied by EP not only to
perceptual systems, but to cognitive and
behavioural ones as well (more on this
later…)
Levels of Causation
•
•
•
•
Proximate (or Mechanistic)
Developmental (or Ontogenetic)
Phylogenetic (or Historic)
Ultimate (or Functional)
•
•
•
•
•
Food sharing between family members
Breast feeding
Monogamy
Language
Sibling rivalry
Levels of Causation
• Different areas of science operate at
different levels
• Very different explanations may all be
correct, just at different causative levels
• Even sub-disciplines of psychology operate
at different levels
• Depending on the topic of focus, EP may
also be operating at different levels
History of Evolutionary Theory
• Did not start with Charles Darwin
• All evolutionary theories address: “how do
organisms change with time?” and “how do
new organisms develop?”
• Greeks
– Thales and Empedocles: change across
generations
– Aristotle: strict, rigid hierarchy
• Francis Bacon (1561-1626)
– Novum organum (1620); variation across
generations
• Gottried Leibniz (1646-1716)
– Ammonites & nautilus; environment causes
change
• George Leclerc, Comte de Buffon (17071788)
– Adaptation to fit environment
– e.g., N.Am bison from ox
• Immanuel Kant (1724-1804)
– Apes could develop the abilities of reasoning
beings
• Erasmus Darwin (1731-1802)
– Single source of beginning of life
– Competition as driving force of
evolution
– Sexual reproduction, The Botanic
Garden
• Baron Georges Cuvier (17691832)
– Catastrophism: periodic extinction
of species
• Jean-Baptiste Lamarck
–
–
–
–
Gives mechanism for evolutionary change
Movement towards higher forms
Individuals change during lifespan
Inheritance of acquired characteristics (i.e.,
changes passed to offspring)
Charles Darwin
• Lots of geology and entomology
• Voyage of the Beagle (18311836)
• Existence of adaptations
• Read Malthus’ Essay on the
Principle of Population
– Not everyone can survive
Darwinian/Natural Selection
• 1837: started notebook on
“transformation of species”
• On the Origin of Species (1859)
• Variation, inheritance, selection
• Provided causal mechanism
• Selection
– Artificial, natural, sexual
• Not intentional, gradual, differential
reproductive success
Alfred Wallace
Requirements of Evolution
• Heritable variation
• Differential reproductive success
Gregor Mendel
• “Founder” of modern
genetics
• Experiments with pea plants
(also fuschia, maise, etc.)
• Particulate inheritance
• “Gene”
• Darwin didn’t know
anything about this…
Social Darwinism
• Herbert Spencer (1820-1903)
–
–
–
–
Applied evolution to everything
Animals, human mind, society
“Survival of the fittest”
Directed, purposeful
• Helping the weak limits society
– Government should not be involved in social
programs
• Appreciated by 19th C. American
industrialists
– e.g., “The growth of a large business is merely
survival of the fittest…” (J.D. Rockefeller)
– e.g., “All is well since all grows better.” (A.
Carnegie)
Francis Galton
• Charles Darwin’s cousin
• Developer of modern field of
psychometrics
• Early use of twin studies to
understand heritability of
intelligence (Hereditary Genius)
• Argued traits from EEA useful in
modern period (e.g., social nature,
gregariousness)
• Eugenics movement
Eugenics
•
•
•
•
•
•
Improve society by selective breeding
Not a new idea, e.g., Greek city state Sparta
Herbert Spencer
Hitler
Alberta Eugenics Board
Environment changes; necessary to predict
future…
Evolved Instincts
• William James
• Humans possess inherited, evolved instincts
• But environment and learning can modify
many “instinctive” behaviours
• Now, better to say “biological
predispositions”
Standard Social Science Model
(SSSM)
• Nature vs. Nurture issue
• Shift to importance of environmental factors
in behavioural regulation
• Early Behaviorists, developmental and
social psychology
• Tabula rasa, total modifiability, culture as
autonomous force, behaviour via general
learning rules
Nature via Nurture
• Much of psychology studied at proximate
level of causation
• Genetic and Environmental interaction is a
constant
Sociobiology
• E.O. Wilson
• Behaviours affect reproductive
success, and behaviours
influenced by genes
• Ergo, evolutionary selection has
helped shape human behaviour
• Fears of a new social
Darwinism
Risks for EP
• Teleological assumptions; evolution has no
“end-goal”
• Assuming all modern traits must be derived
from selected-for adaptations
• Arguing without sufficient evidence (“justso stories”)
Solutions
• Study gene-environment-behaviour interactions
– Behavioural genetics (won’t indicate if a trait is an
adaptation, though)
• Comparative approach
– Cross-species comparisons
• Cross-cultural approach
– Behavioural “universals” across time and space;
complicated due to environmental contingencies
• Mathematical and computational modeling
– Genetic algorithms, game theory, neural networks
Misconceptions about EP
• A variety of misunderstandings
• Many derive from a broader
misinterpretation of general evolutionary
theory
Everything is an Adaptation
• Not all present traits must have
been adaptively selected
• Spandrel
– Non-adaptive trait as side-effect of
an adaptive one
• Exaptation
– Trait shaped by evolution for a
specific purpose that is
subsequently coopted for a new use
• Sensory bias
– Trait as side-effect of
sensory/perceptual system
EP is Deterministic
• “Genetic determinism”
• Remember, genetics interacts with
environment
• Actually, relatively low heritability of many
behavioural traits
• Effects of learning very significant
• E.g., Abbey (1982), Buss (1994): woman
smiles, man misinterprets
EP is Reductionistic
• Reductionism: taking something down to its
most constituent parts
• Sometimes rather absurd
• Levels of causation
• Certain degree of reductionism very useful
in science
EP Argues for Optimal Design
• No organism is fully optimized
• Evolution: “good enough” to last long
enough to reproduce
• Evolutionary time-lag
– E.g., clogged arteries and heart attacks
• Costs of adaptation
– E.g., fear of snakes and spiders, not cars
EP is Politically Incorrect
• Science
• Social-cultural elements
Field in Progress
• EP is a developing field
• Disagreement over underlying theory
EP, Santa Barbara Style
• Late 1980s - early 1990s, Leda
Cosmides & John Tooby
• University of California, Santa
Barbara
– Center for Evolutionary Psychology
• Formalized the developing field of
EP
– Adapted Mind (1992)
•
•
•
•
Universal human trait adaptations
EEA; slow evolutionary development
Cognitive modules
Currently, most well-known and
popular(ized)
Universal Traits
• Politically correct
– Specter of sociobiology
– Avoids claims of racism
• Cognitive psychology
– Specific link between cognition and genes not well
understood
– Physiology and (some) gene interactions better
understood
• Therefore, look for pan-human attributes
Slow Evolution
• Older biology, evolution, genetics operated
on assumption of slow evolutionary change
• Made Pleistocene mind in modern body
assumption reasonable
• Modern research challenging this
Hawks et al. (2007)
• Linkage disequilibrium study of the HapMap
genotype data set
• Recent selection (within last 10,000 years) on
1800 human genes
– Ascertained selected variants
– About 7% of human genes
• Indicates that human evolution has actually
increased over last 50,000 years
– Population increase, cultural development, ecological
modification
Wang et al. (2006)
• Identified biological functional categories for
recently (less than 40,000 years) selected human
gene function
• Non-random (indicating specific human relevant
selection pressures)
• Pathogen-host interaction, reproduction, DNA
metabolism, cell cycle, protein metabolism, and
neuronal function
• Neuron function includes genes for:
– Serotonin transporter, glutamate and glycine receptors,
olfactory receptors, synapse-associated proteins, and
numerous brain-expressed genes with largely, as yet,
unknown function
Cognitive Modules
• Idea that specific brain “units” have evolved
for specific, ancestral tasks
• Little/no change from ancestral form
• Each module for single function
• Cognitive science argues for brain as
general pattern classifier
• More on this later in course…
Popularized
• Evolutionary psychology; catchy name
• Santa Barbara school the early adopter
• Numerous popular-press books
Caveat
• Issues with some underlying assumptions
do not invalidate value of applying
evolutionary theory to psychological topics!
• Scientists (in any field) frequently debate
assumptions, findings, and interpretations
• Other evolutionary approaches
Human Behavioural Ecology
(HBE)
• Applies principles of evolutionary theory
and optimization to human behavioural and
cultural diversity
• Early roots in ethology and sociobiology
• Modern HBE studies evolution and adaptive
design in ecological context
Dual Inheritance Theory (DIT)
• Culture and genes provide separate, but
linked, systems of inheritance and variation
• Cultural information affected by natural
selection, decision making (genetic and/or
culturally evolved preferences) and
transmitter influence
• Often utilize explicit mathematical models
Summary Comparison
HBE
EP
DIT
Explanatory Focus
Behavioural
strategies
Psychological
mechanisms
Cultural evolution
Key Constraints
Ecological, material
Cognitive, genetic
Structural,
information
Temporal Scale of
Adaptive Change
Short-term
(phenotypic)
Long-term (genetic)
Medium-term
(cultural)
Expected Current
Adaptiveness
Highest
Lowest
Intermediate
Hypothesis
Generation
Optimality and ESS
models
Informal inference
Population-level
models
Primary Hypothesis
Testing Methods
Quantitative
ethnographic
observation
Survey, laboratory
experiment
Mathematical
modeling and
simulation
From: Winterhalder & Smith (2000)
EP, HBE, DIT
• Traditionally viewed as competing fields
– Different assumptions, analytic methods, alliances with
other disciplines, academic politics
• Increasing recognition of complementary integration
– Take advantage of different study methodologies,
empirical foci, time scales of adaptation, behavioural
domains
• Limits to complementarity
– The same behaviour can’t simultaneously be the product of
each field’s underlying assumptions
– But, different these field’s hypotheses could be
simultaneously true for different behaviours
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