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Lecture 7

PSYC 2P25 Lecture Notes - Lecture 7: Heterozygote Advantage, Impulsivity, Novelty Seeking

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Michael Ashton

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PSYC 2P25 October 29th, 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
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PSYC 2P25 October 29th, 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
o E.g. Trinidadian guppies
Below waterfalls, may be eaten by predators (pike). Above waterfalls, no
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
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
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
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-
For hunter-gatherers, novelty seeking promotes continuing search for
better areas to hunt and gather
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