Notes truncated due to length constraints
Foundations of Evolutionary Psychology (Notes)
Four guiding questions of evolutionary psychology
- Why is the mind designed the way it is? What causal processes shaped its current form?
- How is the mind designed? What are its mechanisms or component parts, and how are they organized?
- What are the functions of the component parts and their structure—what is the mind designed to do?
- How does current environment input interact with mind design to produce observable behavior?
The human brain and mind as the focus of an evolving science
- The brain is the most complex organic structure (~) and a central focus for studying mind-brain mechanisms from an evolutionary perspective.
- Evolutionary psychology pulls findings from brain imaging, learning & memory, attention, emotion, attraction, kinship, cooperation, ethics, culture, consciousness, and more.
Early history and the emergence of evolutionary thinking
- Evolution refers to change over time in life forms; pre-Darwin evidence suggested change over time (Lamarck, Cuvier, embryology, fossil record).
- Lamarck (1744–1829): inheritance of acquired characteristics; natural tendency toward higher forms; example of giraffes’ long necks via attempts to reach higher leaves. Modern evidence also considers mate competition in long-necked giraffes.
- Cuvier (1769–1832): catastrophism; species extinguished by sudden catastrophes and replaced.
- Before Darwin, evidence for change over time included: morphological similarities across species, embryological resemblance, fossil records showing change, and functional design features (e.g., beaks adapted to nuts).
- Adaptations appeared to have purpose or function (porcupine quills, turtle shells, beaks) but a causal mechanism for change was lacking prior to Darwin.
Darwin’s theory of natural selection: the three essential ingredients
- Variation exists within populations; not all variants are identical.
- Inheritance: some variation is heritable and reliably passed to offspring.
- Differential reproductive success: heritable variants affect survival and reproduction, changing allele frequencies over generations.
- Formally: natural selection is the differential reproduction of inherited variants (the “bottom line”).
- Note: Darwin also drew on Malthus’s principle that populations tend to overproduce, creating a struggle for existence, with favorable variations preserved and unfavorable ones eliminated.
- The three ingredients are the core of natural selection; evolution occurs through differential reproductive success across generations.
- Darwin’s work culminated in a unifying theory linking variation, heredity, and differential reproduction to the origin of new species and the modification of existing adaptations.
Darwin’s theory of sexual selection
- Some traits evolve not because of survival advantage but due to mating advantages.
- Two primary mechanisms:
- Intrasexual competition: members of the same sex compete for mating access (e.g., stags locking horns). Winning traits become more common because they increase mating success.
- Intersexual selection (female choice): one sex prefers certain traits in mates, increasing their frequency (e.g., peahens prefer vivid plumage; gift-giving in some species).
- Outcomes that initially puzzled Darwin (e.g., the peacock’s tail) become explained via sexual selection.
- Consequences: sexual dimorphism often arises (e.g., males larger due to competition) as a byproduct of selection for mating success.
The Role of Natural Selection and Sexual Selection in Evolutionary Theory
- Other evolutionary forces exist beyond natural/sexual selection:
- Genetic drift: random changes in allele frequencies.
- Mutation, founder effects, genetic bottlenecks contribute to drift.
- Example: a small founding group with an unusually high frequency of a gene (e.g., red hair) can shape the population.
- Natural selection is the primary cause of adaptation, but drift can also change genetic makeup.
- Evolution is not forward-looking or intentional; it acts on existing variation and cannot foresight future needs.
- Evolution is gradual over many generations; punctuated equilibrium describes periods of rapid change in small increments, separated by longer periods of stasis.
- Darwin’s theory linked all life through a common tree of descent, highlighting human kinship with other species (e.g., humans and chimps share substantial DNA similarity; common ancestor ~ ago).
- Early objections to natural selection included:
- Lack of a robust inheritance mechanism (Darwin favored blending inheritance—later shown incorrect).
- The problem of intermediate stages: how could partial forms be advantageous? This is resolvable when partial adaptations can confer benefits (e.g., partial wings still offer warmth or mobility).
- Religious objections to human origins via natural processes.
- The Modern Synthesis later resolved inheritance issues by endorsing particulate inheritance (Mendelian genetics) and integrating genetics with natural selection.
The Modern Synthesis: Genes and Particulate Inheritance
- Mendel showed inheritance is particulate: genes are discrete units passed intact to offspring; parental genes are not blended.
- Genotypes vs. genes:
- Gene: smallest discrete unit of inheritance.
- Genotype: total set of genes an individual carries; genotypes are reshuffled each generation in sexually reproducing species.
- The Modern Synthesis (1930s–1940s) reconciled Darwinian natural selection with Mendelian genetics, discarding Lamarckian inheritance and blending inheritance, and clarifying the genetic basis of evolution.
The Ethology Movement and early biological study of behavior
- Ethology emphasized evolution and function in behavior; imprinting was a key phenomenon.
- Imprinting: a rapid, preprogrammed form of learning during a critical period, leading to attachment to the first moving object (often the mother).
- Konrad Lorenz’s work on imprinting and critical periods helped establish ethology as a discipline and linked behavior to evolutionary adaptation.
- Four “whys” of behavior (Tinbergen):
- Immediate causes (proximate mechanisms)
- Developmental influences
- Adaptive function (survival/reproduction)
- Evolutionary history (phylogeny)
- Fixed action patterns: stereotyped sequences triggered by a specific stimulus and carried out to completion.
- Ethology foreshadowed the idea that behavior can be understood as an evolved adaptation.
The Inclusive Fitness Revolution (Hamilton)
- Inclusive fitness broadens the notion of fitness beyond an individual’s direct reproductive success to include effects on relatives who share genes.
- Key idea: genes are replicated when their copies are passed on, not only via direct offspring but also via kin.
- Formal concept:
- Inclusive fitness = direct fitness + the sum of the effects of an individual’s actions on the reproductive success of genetic relatives, weighted by genetic relatedness.
- Genetic relatedness coefficients (examples):
- Brothers/Sisters:
- Grandparents/Grandchildren:
- First cousins:
- Hamilton’s rule for altruism: rB > C, where B is the benefit to the recipient, C is the cost to the actor, and r is relatedness.
- Implications for psychology and behavior: altruism should be more common toward close relatives; kin selection shapes social behaviors.
- Hamilton’s work transformed evolutionary biology and influenced thinking about family, altruism, groups, and aggression.
Clarifying Adaptation and Natural Selection (George C. Williams)
- Williams contributed three major shifts:
1) Downplayed group selection as a primary force; emphasized gene-level selection.
2) Helped popularize inclusive fitness as a central concept, clarifying how gene replication can be promoted via kin.
3) Offered rigorous criteria for identifying adaptations: reliability, efficiency, and economy.
- Reliability: mechanism develops in most members of a species across environments and performs reliably where it is designed to function.
- Efficiency: mechanism solves an adaptive problem effectively.
- Economy: benefits exceed costs; avoids undue resource expenditure.
- Williams emphasized a gene-centered view of adaptation and influenced later work on what constitutes an adaptation.
- The idea that adaptations are not
- Williams contributed three major shifts:
1) Downplayed group selection as a primary force; emphasized gene-level selection.
2) Helped popularize inclusive fitness as a central concept, clarifying how gene replication can be promoted via kin.
3) Offered rigorous criteria for identifying adaptations: reliability, efficiency, and economy.