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Nettle, D. (2006). The evolution of
personality variation in humans and
other animals. American
Psychologist, 61 (6), 622-631.
Presentation by: Nikoo Naimi and Sarah
Krouse
Research Basis
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Previous research hasn’t paid much attention to
variation in traits because they believed, due to
natural selection, important traits would not have
much variation.
Tooby and Cosmides (1992), Buss (1991), and
Buss and Greiling (1999) suggest, however, that
there may be some heritable variations that serve
a functional purpose.
Nettle, D. (2006). The evolution of personality variation in humans and other animals.
American Psychologist, 61 (6), 622-631.
Variation through Trade-Offs
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It is suggested that variation can come about
through trade-offs. Where individuals within the
same normal range of a personality dimension
may achieve the same levels of fitness through
different means.
This means that some tradeoff exists, where if one
component of fitness is maximized by increasing a
trait, another component will suffer.
Nettle, D. (2006). The evolution of personality variation in humans and other animals.
American Psychologist, 61 (6), 622-631.
Purpose of Article
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To review variation between individuals in
nonhuman species, especially in functionally
relevant traits.
To review how a different traits in the five-factor
model of personality can be seen as a cost or
benefit depending on the situation.
Nettle, D. (2006). The evolution of personality variation in humans and other animals.
American Psychologist, 61 (6), 622-631.
Variation in Non-human Species
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Especially in functionally relevant traits
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Example:
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Within the pygmy swordtail, large males are desired but
take longer to develop. Smaller males develop sooner
and are able to sneak up on the women and copulate
with them. Therefore, there is a trade-off of costs and
benefits to each variation. Different contexts yield
different advantages to each variation.
Nettle, D. (2006). The evolution of personality variation in humans and other animals.
American Psychologist, 61 (6), 622-631.
Five Factor Model of Personality:
Predicted Benefits and Costs
Personality Traits
Benefits
Costs
Openness
Creativity, which leads to mating
success
Leads to paranormal beliefs and psychosis
Conscientiousness
Longer life expectancy; attention to
long term goals
Overlooking spontaneous reproduction
possibilities; associated with eating disorder and
obsessive compulsive disorder
Extraversion
Have more mates; explore their
environment
Expose self to risk; lack of family stability
Agreeableness
Aware of others’ mental states;
avoid violence; cooperative; valued
friend and coalition partner
Excessive trusting in others; missing out on
Avoiding dangerous situations;
detecting and quickly reacting to
threats; motivating competitiveness
Psychiatric disorders (i.e. depression and
stress); damages to physical health
Neuroticism
opportunities
Adapted from Nettle, 2006, p.628
Nettle, D. (2006). The evolution of personality variation in humans and other animals.
American Psychologist, 61 (6), 622-631.
Conclusions
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There is considerable variation in each trait, and depending
on the context and situation, each trait may be seen as
beneficial or harmful.
Evolution results in considerable variation within animal and
human populations. The notion of trade-offs has been used
to explain diversity, because, due to selection, fluctuations in
the environment lead to variation in phenotypes.
Nettle, D. (2006). The evolution of personality variation in humans and other animals.
American Psychologist, 61 (6), 622-631.
Critical Review Comments
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Interesting Points
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Fluctuations in the environment lead to heritable variation (e.g. Galapagos
finches).
In nonhuman species, fitness functions are not necessarily unimodal (e.g.
two male morphs in coho salmon).
Openness is associated with depression and schizophrenia.
Points of Weakness
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Trade-offs and fluctuating selection are not the only possible explanations
for heritable variation.
No experimental design to test hypothetical costs and benefits of trait
variation.
Does not provide readers with definitions of agreeableness and openness.
Nettle, D. (2006). The evolution of personality variation in humans and other animals.
American Psychologist, 61 (6), 622-631.