PSYC20009 Lecture Notes - Lecture 11: Balancing Selection, Walter Mischel, Pleiotropy
10 May 2018
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Week 11
- Personality description = how, the way in which people differ, traits + characteristic
adaptations + life narratives
- Personality explanation = why, the ‘reasons’ there are differences
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- Personality might partly reflect phylogenetically old processes: cross cultural data →
structure of traits appear universal (Big Five structure confirmed in 56 nations,
Schmitt et al., 2007); cross species data → correlated suites of behaviour,
analogues of the Big Five traits found in many non-human animals, ALL Five traits
observed only in chimpanzees and humans (Gosling & John, 1999)
- Behavioural genetics: genetic variation explains 40-50% of the variation in
personality traits, reflects evolutionary forces, perhaps personality traits reflect
evolved psychological mechanisms - an adaptation: selected for due to its impact on
fitness, a by-product: trait that is coupled with an adaptation, but was not itself
selected for (e.g. belly button), noise: traits that are not adaptations or by-products
- Adaptative traits: plausible (reasonable) that personality traits can be adaptative and
‘selected for’, analogy - the domestication of the dog (grey wolf), early wolf-human
interactions likely to favoured certain ‘traits’ (fearlessness/ ‘flight distance’, placidness
- not aggressive towards humans), breeders explicitly ‘select for’ traits (Labradoodle),
Dmitri Belyaev → started experiment in 1950s to redomesticate the dog, done with
Russian Silver Foxes, placidness selected for over successive generations,
interbreed silver foxes most placid (shown by simple behavioural test of putting hand
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into enclosure with foxes and selecting them if they interact more placidly and
submissively), found changes in characteristics (psychological + physical) → more
playful, friendly and dog-like, coats changed colour, floppy ears, curly tail
- Environment of evolutionary adaptedness (EAA, the Pleistocene - very different from
today): some challenges were not present in our EAA (seatbelts, locks, insurance,
personal alarms) but many challenges were present in some form (safety, avoiding
threats)
- Adaptive traits: Neuroticism/Conscientiousness/Openness - survival?;
Extraversion/Agreeableness - reproduction?
- Asking whether neurotic/conscientious tendencies are adaptive is not the same as
asking whether variation in those tendencies is adaptive
- Tooby & Cosmides (1990): natural selection drive towards universals, it does not
favour systematic variations, selects more adaptive phenotypes and drive evolution
of species towards that, personality traits are not adaptations (just noise, evolved
design for human nature, traits are variations around design, variations are not
important → random noise, different apples different shapes for no reason), analogy:
gut-packing design → wondrous variability in the exact route taken by our intestines
on the way to colon
- Trait distribution (normal bell curve), mean level reflects optimisation via natural
selection, selective neutrality (fitness-neutral genetic mutations i.e., random
variations that have no impact on fitness) may accumulate over time to increase
genetic variance in a trait), problem → if genetic variations underlying personality are
really fitness-neutral then personality variation should not predict fitness-relevant
outcomes, if variation in personality has no adaptive significance we shouldnt see
any correlations between measures of personality traits and any kind of other
variable that is useful in environment for evolutionary adaptiveness for survival and
reproduction
- But they do → health (high agreeableness, low neuroticism), longevity (high
conscientiousness), reproductive behaviour (high extraversion), appear completely
unlike gut-packing design
- Balancing selection: multiple selection pressures influence evolution of single traits,
one version - antagonistic pleiotropy (fitness trade-offs, trade off one benefit against
a cost) → sociable, outgoing Extraverts tend to have more sexual partners (favouring
reproduction) but quieter, calmer introverts have fewer accidents (favouring survival)
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- But for antagonistic pleiotropy to work in the long term, these must be in perfect
balance
- Alternative version - Environmental Heterogeneity → Environments may consist of
niches favour different kinds of behaviour (The early bird gets the worm, but the
second mouse gets the cheese. (Pinker, 2009); suggests a variation in the selection
pressures applied to a species (against the idea of natural selection always driving
toward a universal design), Analogy: Big vs. small pets…
- Suggestive data by Camperio, et al., 2007: Family histories of Italians, island
dwelling vs coastal-mainland dwelling –and big five traits, Italians whose families
resided on islands for at least 20 generations have lower extraversion and openness
scores than both coastal mainland Italians and those whose families recently settled
on the islands more recently, Indicative of environmental niches, can’t be explained
by cultural variables
- Niche can also occur in social environment: frequency dependent selection → if all
your neighbours are pursuing one strategy it may pay to pursue another, hawk-dove
game (hawk and doves compete for food resources, hawk compete aggressively;
doves back down as soon as their opponent initiates any aggressive behaviour; 2
doves share)
- Hawks often win, but Doves are never injured (calorie loss), In a population with
many Hawks it pays to be a Dove (not gaining calories, but not losing them), In a
population with many Doves it pays to be a Hawk (easy wins with no injuries),
Neither represents an evolutionarily stable strategy; but each is adaptive in the
context of the other
- Agreeableness: In a world of trusting, obliging people it would be very easy to exploit
people for your own gain, But if there were too many disagreeable people everyone
would be exploiting everyone else, This logic has been suggested to explain the low
(but steady) prevalence of psychopathy
- Life History Theory: Principles: 1) Resources vary in their availability over time and
space, 2) Fitness maximization is not a one-shot game (long vs. short term
strategies), 3) Trade-offs must be made (reproduce now or wait for better
circumstances, quantity or quality of offspring, focus on mating or rearing)
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