Evolutionary Psychology
How are humans relatively homogenous species
- Greater than 80% of genetic diversity among people can be found within the same population; -less than 10% of human genetic variability is attributed to differences among people coming from different continents. -Chimpanzees are about four times more genetically diverse than humans -This suggests that "race," although it may have important sociological significance, has minimal biological significance
Evolution works at all stages of development, but not necessarily equally
- Selection will have greatest effects on early stages of development: Getting born Developing to sexual maturity Finding a mate Rearing offspring to reproductive age Any benefits that encourage development through these stages will be favored, even if they have negative effects later on.
Famous remains of Human species found
-3 years old Taung Child (Austrolopithecus africanus) Raymond Dart, 1924 -12 years old Turkana Boy (Homo erectus) Richard Leakey, 1984
Products of natural selection
-Adaptations (umbilical cord) -Inherited -Develop reliably -Solve problems of survival or reproduction -Most are species-typical -Byproducts of adaptations—no functional design (e.g., belly button) -Noise—random effects, independent of adaptations (e.g.,"iny" vs. "outy")
Darwin also assumed (as does mainstream evolutionary psychology) that..
-Change occurs gradually over millions of years (i.e., sudden changes, or saltations, do not produce new species) -Natural selection is the creative force in evolution -Selection occurs only at the level of the individual, not the level of the group or the species
Evolutionary Psychology is
-Consilient -Organizes known facts parsimoniously! -Provides guidance to important domains! -Leads to new predictions! -Unifies psychology with the life sciences! -Can serve as a metatheory for other areas of Psychology!
Soft modularity (Geary & Huffman, 2002)
-Domain-specific information-processing modules evolved to handle recurrent problems faced by our ancestors -When environments are stable; invariance over contexts ! Domain-general information-processing mechanisms also evolved -Necessary to deal with novelty
Does evolutionary psychology reflect genetic determinism?
-Evolutionary psychology takes as, gene's eye view -Richard Dawkins' "selfish gene" proposal -Impression of genetic determinism
From apes to humans
-Humans did not evolve from chimpanzees -Humans last shared a common ancestor with chimpanzees 6-8 million years ago -Estimate is based on fossil and genetic data
Tinbergen's (1951) four questions
-Immediate (proximal) influences (causes) -Function of a behavior ("adaptive purpose") -Ontogenetic (developmental) influences -Phylogenetic (evolutionary) origins
Identifying Adaptive Problems—Guidance from:
-Inclusive fitness theory -Human universals -Traditional societies -Archeological record -Current psychological mechanisms -Task analysis
Sexual selection
-Intra-sexual competition (fighting to get mate) -Inter-sexual selection (preferential mate choice) based on aesthetics -Female choice
Pongo pygmaeus
-Oranguatuns
Disadvantages and Advantages of varied species. (example)
-Over the period of the drought, the number of large-beaked birds increased and the number of small-beaked birds decreased -Several years later, however, the climate changed, and small plants with small seeds proliferated, giving the foraging advantage to the small-beaked birds. -Over several generations, the distributions changed, and small-beaked birds outnumbered the large-beaked ones ****It depends on which environment a bird is hatched into, and this cannot be anticipated by the genes.
Natural selection is not
-Purposive -Forward looking -Progressive -The "best" solution for an adaptive problem
Grant & Grant noted
-Relationship between beak size, availability of resources, and survival -Beak size varies, from small to large, among one species of Galápagos finches -Large beaks are better suited to cracking large seeds, whereas the small beaks are better suited to handling small seeds. -In a period of drought, there were fewer small-seed plants, giving the larger-beaked birds an advantage over the smaller-beaked ones. -Even those small-beaked birds that survived were at a mating disadvantage to their bigger-beaked cousin
How to identify adaptations?
-Reliability -Efficiency -Economy -Improbable Usefulness
Environment of Evolutionary Adaptedness (EEA)
-Selection pressures that occurred during an adaptation's period of evolution responsible for the adaptation -The EEA for each adaptation refers to the selection forces,or adaptive problems, that were responsible for shaping it over deep evolutionary time -EEA different for different adaptations; evolutionary psychologists emphasize EEA for when uniquely human abilities emerged: Pleistocene, last 2 million years
Darwin's (1859) theory of natural selection
-Superfecundity -Variation is characteristic among members of a species -Variation is heritable -Characteristics that result in individuals surviving and reproducing tend to be selected as a result of the interaction between the individual and the environment
A Functional Analysis Pregnancy Sickness as an Adaptation
-Symptoms: nausea, vomiting, food aversions -It corresponds to the time in prenatal development when embryo is most susceptible to effects of teratogens -Modern women acquire aversions to foods that are high in toxins (e.g., meat, coffee, alcohol) -Despite variability, pregnancy sickness in universal -Reduction in incidence of spontaneous abortions for women who experience pregnancy sickness
Evolutionary Psychology focuses on four key questions
-Why is the mind designed the way it is - what causal processes created, fashioned, or shaped the human mind into its current form? -How is the human mind designed - what are its mechanisms component parts, and how are they organized? -What are the functions of the component parts and their organized structure - what is the mind designed to do? -How does input from the current environment, especially the social environment, interact with the design of the human mind to produce observable behavior?
Natural selection
-Works with what is already available -Adapts individuals to immediate/local environment -Economical (parsimonious)
Evolved psychological mechanisms are_________
-functional: Designed to solve statistically recurrent adaptive problems
What evolved are
-psychological mechanisms (information processing mechanisms are the "missing link" in evolutionary explication)
Pleiotropy
A gene can have multiple effects, sometimes at different times in development
Some Basic Concepts and Principles of Evolutionary Developmental Psychology
All evolutionarily-influenced characteristics in the phenotype of adults develop, and this requires examining not only the functioning of these characteristics in adults, but also their ancient origins and their ontogeny.
"In the distant future . . . psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation."
Charles Darwin
Humans ________ evolve from chimpanzees.
Did Not
The key to natural selection
Differential reproductive success because of heritable variants; everyone has ancestors, but not everyone leaves descendants
Nothing in psychology makes sense except in the light of evolution
Every evolutionary psychologist
Darwin Was Deeply Troubled by
Facts that Could not Be Explained by Natural Selection
Gorilla gorilla
Gorillas
The primary questions for EDP are:
How can an understanding of our species' phylogeny help us better understand our current ontogeny? How can an understanding of human ontogeny help us better understand human phylogeny? How do evolved, inherited information-processing mechanisms become expressed in the phenotypes of adults?
Where did humans come from?
Humans are primates, closely related to apes, and less-closely related to monkeys (watch youtube video for more info, located in the class notes)
Degree (percentage) of genetic relatedness among different types of relatives
Identical twins: 100 Parents & children: 50 Full siblings: 50 Grandparents & children: 25 Uncles/aunts & nieces/ nephews: 25 Half siblings: 25 First cousins: 12.5 Second cousins: 6.25 Adopted siblings: 0
Domains of Mind
Information processing mechanisms are relatively independent, domain-specific modules designed to solve recurrent problems faced by our ancestors
Fitness (Darwin's definition)
Number of offspring one has
Genetic difference from humans
Orangutans - 2.4% Gorillas - 1.4% Bonobos/pygmy chimpanzees - 1.2% Common chimpanzees - 1.2%
Thalidomide babies
People use to take medication to reduce or not have "morning sickness" from pregnancy. It worked but, this caused mutations making babies form flipper-like limbs
George Williams theory of senescence:
Positive effects early in life may have negative consequences later in life, resulting in death
Adaptation
Reliably developing, inherited characteristics that came about as a result of natural selection and helped to solve some recurrent problems of reproduction or survival in the environment of evolutionary adaptedness
Lifestyles in EEA
Small groups (likely no more than 30-60 individuals) ! Increasing social complexity over hominid evolution ! Food economy ! Gathering ! Scavaging ! Hunting ! Extended maternal care for infants (4-5 years) ! Marginally monogamous/polygamous ! Degree of sexual dimorphism ! Number white blood cell types in modern humans most like polygamous gorilla and monogamous gibbon than promiscuous chimpanzee (Nunn et al., 2000) ! Size of male testes between gorilla and chimpanzee Females probably reached puberty and had first birth relatively late (late teens, early 20s) ! Substantial climatic changes over last 2 million years (i.e., EEA not stable) ! Females likely relocated to the villages of their mates ! Same pattern as in chimpanzees ! Patterns for most hunter/gatherers ! Genetic evidence (more world-wide variation in mitochondrial DNA than DNA on Y chromosome)
Classic fitness
Sum of one's own reproductive success
Inclusive fitness (Hamilton)
Sum of one's own reproductive success (classic fitness).. plus the effects the individuals actions has on reproductive success of genetic relatives
Evolutionary Developmental Psychology (EDP)
The application of the basic principles of Darwinian evolution, particularly natural selection, to explain contemporary human development. It involves the study of the genetic and environmental mechanisms that underlie the universal development of social and cognitive competencies and the evolved epigenetic (gene- environment interactions) processes that adapt these competencies to local conditions; it assumes that not only are behaviors and cognitions that characterize adults the product of natural selection pressures operating over the course of evolution, but so also are characteristics of children's behaviors and minds.
Basic tenet of evolutionary psychology
The human mind has been prepared by natural selection, operating over geological time, for life in a human group
Nothing in biology makes sense except in the light of evolution
Theodosius Dobzhansky
Evolutionary psychology
Understanding the human mind and behavior from an evolutionary perspective.
Homo sapiens________
are a relatively homogenous species
Evolved psychological mechanisms
are instantiated in the brain. Evolved psychological mechanisms can be described as information processing devices. Inputs Decision Rules Outputs
Pan paniscus
bonobos, or pygmy chimpanzees
Pan troglodytes
common chimpanzees
Changes in beak size in Galápagos finches (Grant & Grant) -
example of microevolution
View from evolutionary psychology
genes------> Domain-specific information- processing mechanisms------> Behaviors (elicited in appropriate contexts)-------> Survival, reproductive success, and selection of genes
Homo Sapiens
humans