Transcript What are the basic principles of evolutionary theory?

Psychology 305A:
Theories of Personality
Lecture 6
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The Biological Perspective
1. What are the basic principles of evolutionary theory?
2. How have the basic principles of evolutionary theory
been adapted to the study of personality?
3. What hypotheses has the evolutionary approach
generated regarding (a) altruism and (b) sex
differences in the desire for sexual variety?
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By the end of today’s class, you should be able to:
1. describe natural selection, sexual selection, intrasexual
selection, and intersexual selection.
2. generate examples of distinct forms of selection.
3. define the term “inclusive fitness.”
4. review research supporting evolutionary hypotheses
related to altruism.
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5. define the terms “reproductive capacity” and “minimal
parental investment.”
6. review research supporting evolutionary hypotheses
related to sex differences in the desire for sexual
variety.
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What are the basic principles of evolutionary theory?
• According to Darwin’s theory of evolution, across
successive generations of a species, organisms develop
characteristics that enhance their ability to survive and
reproduce (i.e., adaptations).
• Darwin maintained that there are two processes through
which organisms develop these characteristics:
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1. Natural selection
 A process through which organisms develop
characteristics that enhance their ability to survive.
 Organisms that possess characteristics that enhance
their ability to survive are more likely to live to
reproductive age and to pass these characteristics on to
the next generation.
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 Offspring that inherit these characteristics, in turn, are
more likely to live to reproductive age and to pass the
characteristics on to yet the next generation.
 Through this process, characteristics that enhance the
organism’s ability to survive increase in frequency
across successive generations of the species until
they characterize virtually all members of the species.
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 Example: The preference for sweet, fatty, and salty
foods among humans.
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2. Sexual selection
 A process through which organisms develop
characteristics that enhance their ability to reproduce.
 Darwin maintained that there are 2 mechanisms through
which sexual selection occurs:
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(a) Intrasexual selection
 Occurs when same sex organisms compete for the
sexual interest of the opposite sex.
 Organisms that possess characteristics that enable
them to “win” the sexual interest of the opposite sex are
more likely to mate and to pass these characteristics on
to the next generation.
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 Offspring that inherit these characteristics, in turn, are
more likely to mate and to pass the characteristics on
to yet the next generation.
 Through this process, the characteristics that enabled
the victors to win increase in frequency across
successive generations of the species until they
characterize virtually all members of that sex of the
species.
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 Example: The Ariel Hover Display of the male Bronzed
Cowbird.
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(b) Intersexual selection
 Occurs when organisms of one sex prefer to mate with
organisms of the opposite sex that possess specific,
desirable characteristics.
 Organisms that possess characteristics that are
desirable to the opposite sex are more likely to mate and
to pass these characteristics on to the next generation.
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 Offspring that inherit these characteristics, in turn, are
more likely to mate and to pass the characteristics on
to yet the next generation.
 Through this process, characteristics that are desirable
to the opposite sex increase in frequency across
successive generations of the species until they
characterize virtually all members of that sex of the
species.
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 Example: The brilliant plumage of the male peacock.
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How have the basic principles of evolutionary theory
been adapted to the study of personality?
• Evolutionary psychologists believe that our basic
psychological processes are the product of natural
selection and sexual selection.
• Our psychological processes are seen as adaptations to
the survival and reproductive challenges faced by our
ancestors.
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What hypotheses has the evolutionary approach
generated regarding altruism?
• Altruism: Refers to a desire to help others, even at
the risk of one’s own well-being.
• Theory of inclusive fitness: Organisms are motivated to
enhance their own survival and reproductive potential,
as well as the survival and reproductive potential of
those who are genetically similar to them.
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• On the basis of this theory, evolutionary psychologists
generated two hypotheses regarding altruism.
 Hypothesis A: Helping behaviour increases as the
degree of genetic overlap increases between the helper
and the recipient.
 Hypothesis B: Helping behaviour increases as the
reproductive potential of one’s kin member (i.e., relative)
increases.
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• Burnstein et al. (1994) tested both hypotheses in the
U.S. and Japan.
 Asked participants to imagine that people were
asleep in a rapidly burning building.
 Told participants they could only rescue one person.
 Asked participants to indicate who they would be
most willing to save.
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 In order to test Hypothesis A, participants were
presented with people who varied in their degree of
genetic overlap with the participant.
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 Results consistent with
Hypothesis A.


Tendency
to Help


.50
Highly Related
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.25
.125
Degree of
Genetic Overlap
.00
Not Related
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 In order to test Hypothesis B, the researchers
conducted 2 studies. In the first study, participants
were presented with kin members who varied in age.
In one condition, participants were asked to respond
under the assumption that they lived in an
environment with plentiful resources:
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 Results consistent with
Hypothesis B.


Tendency
to Help



1
10
18
45
75
Age of Kin (Years)
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In another condition, participants were asked to
respond under the assumption that they lived in an
environment with extremely limited resources:
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 Results consistent with
Hypothesis B.


Tendency
to Help



1
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Age of Kin (Years)
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45
75
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 In the second study designed to test Hypothesis B,
participants were presented with kin members who
varied in health.
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 Results consistent with
Hypothesis B.

Tendency
to Help


Healthy


Sick

.50
Highly Related
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.25
Degree of
Genetic Overlap
.125
Not Highly Related
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What hypotheses has the evolutionary approach generated
regarding sex differences in the desire for sexual variety?
• Females and males differ in their reproductive capacity
and the minimal parental investment that is required to
produce an offspring.
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• Reproductive capacity: Males > Females
 Females: Can bear 8 – 12 offspring across the lifespan.
 Males: Can bear an almost unlimited number of
offspring across the lifespan (maximum recorded to
date: 900).
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• Minimal parental investment: Females > Males
 Females: Carry and nourish fetus for 9 months; nurse
child after birth; during lactation, ovulation is suppressed.
 Males: Engage in copulation.
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• Given sex differences in reproductive capacity and
minimal parental investment, evolutionary psychologists
maintain that males and females have developed different
strategies to maximize their reproductive potential.
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• Males: Employ strategies that enable them to copulate
with as many females as possible.
• Females: Employ strategies that restrict copulation to
males who are able to provide care and resources for
the offspring.
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• Following from these strategies, evolutionary
psychologists have generated 2 interrelated hypotheses
regarding sex differences in the desire for sexual variety:
 Hypothesis A: Males are less discriminating in their
selection of sexual partners than females.
 Hypothesis B: Males are inclined to seek more sexual
partners than females.
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• Studies that have tested these hypotheses include:
 Clark and Hatfield (1984)
 Had confederates approach students of the opposite sex
on campus.
 After saying “Hi, I’ve been noticing you around campus
lately and I find you very attractive,” the confederates
asked the students 1 of 3 questions:
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Percent Who Agreed
Male
Female
“Would you go out on a date
with me tonight?”
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“Would you go back to my
apartment with me tonight?”
69
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“Would you have sex with me
tonight?”
75
0
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The Biological Perspective
1. What are the basic principles of evolutionary theory?
2. How have the basic principles of evolutionary theory
been adapted to the study of personality?
3. What hypotheses has the evolutionary approach
generated regarding (a) altruism and (b) sex
differences in the desire for sexual variety?
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