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07 - Heritability and Evolution.docx

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Queen's University
PSYC 100

Week Seven: Heritability and Evolution What are the evolutionary underpinnings of behaviour Genetics What is the relationship between genes, heredity, and behaviour Developmental Psychology: concerned with the environmental variance component, that is, the prenatal and postnatal environmental influences affecting individuals during their lifetimes Evolutionary Psychology: concerned with design of human nature, all human behavioural characteristics that are the product of natural selection in ancestral environments Behavioural Genetics: concerned with the partition of individual differences into genetic and environmental variance components Genetics Review:  Our genetic material, or DNA, is organized into structures called chromosomes that are located in the nucleus of every cell; genes are regions of chromosomes that encode particular proteins  The same genes can be expressed differently depending on interactions with the environment  Much of our understanding of gene’s effects on behaviour come from twin studies, however it is still sometimes difficult to separate genetic and environmental influences Heritability Review:  Genetic influence is measured by a statistic called the heritability coefficient, or h  Heritability is the proportion of observed variance in behaviour that can be attributed to genetic differences among individuals – it is population specific  E.g. any differences between identical twins will have a heritability of zero since genes are not a factor, whereas any differences between a homeschooled household of adopted children with have very high heritability because the children have such similar environments but not genes Genes and Disorders  One Gene, One Disorder (OGOD) Hypothesis: theorize that one gene is responsible for one disorder, or a single specific gene is the causal agent in a specific disorder (popular until recently)  Pedigree Studies: studies follow several generations of families, studying inherited traits/genes  Unfortunately, pedigree studies and the OGOD strategy have not been successful in the area of major mental disorders because the etiology of the disorders does not involve single genes of large effect, instead many genes are involved – they are polygenic  Focus is now on alleles, and The Human Genome Project (which compares people regardless of the kinship status) has allowed for the identification of many markers/chromosomes Variance and Competition  Genes that increase an offspring’s chances of survival (give additive variance) will become more common in the population (have increased gene dosage) until they no longer add survival value, while genes that do not affect survival (have non-additive variance) will continue to vary  Change in Evolutionary Fitness (probability that the line of descent from an individual with a specific trait will not die out) requires additive genetic variance, genetic variance due to gene dosage, as opposed to interactions among different genes (non-additive variance)  When the population reaches maximal fitness, the additive genetic variance is zero (fixation) Natural Selection  Descent with modification through the differential survival of offspring  Genes associated with relative reproductive success increase in frequency over generations, along with the characteristics they code for – thus, changes produced by evolution are inherited  Produces adaptations that have particular survival functions, thus, the ultimate causes of adaptions are the features of the ancestral environment  Not all characteristics are adaptive – some are by-products of other adaptations (e.g. nipples in males), the result of non-selective forces (genetic drift) or pathology (e.g. lesions from infection) Facultative Behaviours: determined by the immediate environment (e.g. pain you feel when your parents divorce – depends on the marriage, family relationship, fighting, financial consequences, etc.) Obligate Behaviours: develop to a large degree independently of variations in environmental context (e.g. pain you feel when you fall down) Evolutionary theories are environmental and selections in orientation because past environments are posited to have selected characteristics of organisms by acting at the level of individual genes Common Evolution Misconceptions  Humans are not more highly evolved than other animals  A specific allele may create a different genetic load (reduction in overall evolutionary fitness for a population compared to what the population would have if all the individuals had the most favoured genotype) at different times or in different environments Naturalistic Fallacy  Determination of what should be based on what is natural; whatever is natural cannot be wrong and we must accept things as they are  E.g. since evolution has designed men to be more aggression and to desire a greater number of sexual partners, aggression and promiscuity are morally good Genetic Deterministic Fallacy  If an organism evolves, the evolution is determined by genes rather than an interaction of genes and environment; genes determine behaviour independently of environmental influences Epigenetics  Traditional thought proposed that inheritance happened as a result of alterations in the DNA sequence, thus an organism cannot pass on characteristics it has acquired through experience  Researchers have now documented cases of epigenetic modification – changes in cellular inheritance not due to changes in the DNA sequence  Epigenetic modification can occur because of environmental experience, which raises the possibility that an acquired characteristic could be inherited by offspring Evolution and Attraction To what extent do genetics affect our attraction to specific individuals Adaptation  Genetics lead us to be attracted to people with desirable genes, however we don’t notice a strand of DNA in their genetic makeup (genotype), you notice their physical characteristics and behaviour (phenotype – outward expression of genotype)  Adaptionist view of the phenotype asks what the function of a particular feature is…  An adaption must meet the following four criteria: o Obviously designed to accomplish some biological
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