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Lecture 7

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Michael Ashton

PSYC 2P25 October 29 , 2012 Evolutionary Function of Personality Evolution by Natural Selection  Individuals differ in various characteristics  These characteristics are (at least partly) heritable  Some of them are associated with number of surviving offspring individuals [the strongest in that setting will survive] o Therefore, frequencies or levels of those characteristics will change across generations o (when a population divides into two, major differences between them an evolve after many generations -> separate species emerge) Evolution and Traits  For most characteristics (traits), evolution leads to uniformity within a species -> “deviant” individuals die out  But why does evolution allow individual differences for some traits?  Some of the reasons involve “trade-offs” associated with high or low levels of a characteristic, but some of the reasons don’t Reasons not involving Trade-offs [not going to be tested]  1) “neutral” genetic variation  2) Mutation/selection balance  3) Resistance to parasites  4) Heterozygote advantage Reasons involving Trade-off  1) Frequency dependence o When most individuals have a given level of trait, some individuals might do better with a different level o E.g. Fish -> Bluegill sunfish  “parenting versus cuckolding”  Some males are “parental” -> build nest after long maturation  Other males are “cuckolding” -> mature earl, sneak into other males’ nests  When cuckolding males are rare, the have high reproductive success (can easily find many parental males’ nests and fertilize there)  When cuckolding males are common, they have low reproductive success (harder to find parental males’ nests not occupied by other cuckolding males)  Thus, success of cuckolding strategy (vs. parenting) depends inversely on frequency of that strategy o E.g. humans PSYC 2P25 October 29 , 2012  Very low levels of Honesty-Humility (H) might be a “strategy” that improves fitness when few others use it  But when many people are very low in H, they no longer thrive because not enough “victims” to go around, and people may become vigilant, retaliatory  Extraversion (X) might also be frequency-dependent:  When few people are high in X, they can easily attract social attention and its rewards (alliances, mates)  But when most people are high in X, then situation changes -> too much “competition” for social attention (so less likely to benefit) and increased “costs” (risks, energies, etc) from “competition” -> might be better off as introverted  2) Fluctuating optimum o “ideal” level of a trait (ie. Fitness), can vary across times and places according to conditions o E.g. Trinidadian guppies  Below waterfalls, may be eaten by predators (pike). Above waterfalls, no predators.  Guppies above falls are much bolder; those below falls much more timid  (differences are heritable -> observed even when guppies are raised in lab)  When predators are removed from stream, “bold” guppies do better (more successful foraging and mating?) and replace “timid” guppies over many generations  When predators added to stream, “timid” guppies do better (don’t get killed) and replace bold guppies over many generations  Thus, bold-vs-timid trade-off in Trinidadian guppies  Boldness better where no predators; timidity better where many predators o E.g. human  Traits (or at least behaviours) related to Honesty-Humility and Agreeableness might differ between farming societies and herding societies  In herding society, much potential for theft of livestock -> promotes emphasis on retaliation and deterrence (e.g. angry, violent response even to minor offense)  In farming society, less potential for theft (crops harder to move) -> favours cooperation and less retaliation  “Novelty-seeking” traits (related to high Openness low Conscientiousness?)  May differ between (sedentary) farmers and (nomadic) hunter- gatherers  For hunter-gatherers, novelty seeking promotes continuing search for better areas to hunt and gather PSYC 2P25 October 29 , 2012  But for farmers, novelty-seeking interferes with routine work of tending crops, etc.  (only indirect evidence so far) Note about Causes of Variation  Evolution can preserve individual differences caused by  1) Genetic differences (whereby genes influence trait levels)  2) Developmental plasticity (whereby genes allow flexible response to environment) Personality Disorders  Patterns of thought/feeling/behaviour that are culturally deviant, are pervasive and inflexible o Begins in teens or 20s o Are stable over time o Cause
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