The Psychology of the Person
Chapter 10 Biological Research
Naomi Wagner, Ph.D
Lecture Outlines
Based on Burger, 8th edition
Heritability of personality traits
Human traits are Polygenic
More and more evidence is accumulating in
support of the heritability of our traits and our
aptitudes. How do we separate environmental
from genetic effects?
The twin study method. Identical
(monozygotic) twins (MZ) share 100% of their
genes. They are compared to fraternal
(dizygotic) twins (DZ), who share Apr. 50% of
their genes. When given a variety of
personality tests, MZ twins’ scores are much
more similar to each other than DZ twins’
scores.
Identical twins share 100% of
their genes
They are formed when a fertilized egg
(zygote) is split , forming two identical
zygotes
Fraternal twins share about 50% of
their genes
They are formed when two different eggs
are fertilized by two different sperm cells
Other Methods to Study Heritability
Please note that the heritability of many
psychiatric disorders has been established
Human characteristics are polygenetic, establish
by more than one gene, a fact which affects the
study of heritability
Other procedures compare adopted children to
their biological parents and adoptive parents,
finding more similarities between the adopted
children and their biological parents.
Heritability (cont-d)
Also, studies comparing MZ twins raised
together vs. MZ twins raised apart find that the
identical twins raised apart are quite similar to
each other, as much as identical twins raised
together, suggesting a strong genetic influence
on personality.
In response, some critics suggest that identical
twins may experience more “shared
environment” than fraternal twins, but this type of
argument is rather weak.
Introverts are NOT Shy
They try to control their level of arousal
The study of extraversionintroversion
The genetic basis for this dimension has been
supported by large-scale twin studies in Sweden
and Finland.
Physiologically, introversion has been
associated with high sensitivity to stimulation
A study in libraries found that introverted people
preferred scheduled area to study in, while
extraverted preferred open, noisy areas.
This study supported the hypothesis of
sensitivity to stimulation.
Who is Happier?
Are extraverted people happier than
introverted? Extraverted people
experience higher levels of positive affect
than introverted.
Maybe because they have more friends,
and also they may be more sensitive than
introverts to information about rewards.
(cont-d)
Regarding happiness, researchers look at
happiness in terms of subjective well being,
which can be divided into positive and negative
affect.
Happiness is obtained by increasing positive
affect and decreasing negative affect.
Though extraverts experience more positive
affect than introverts, they are also more
impulsive, a factor that may get them into
trouble. They may experience more mood
swings than introverted.
Evolutionary Theory and Mate selection
Evolutionary psychology is interested in
understanding the biological basis for human
behavior.
Current human traits and attributes are seen as
evolving in us because they were useful for our
survival in our prehistoric past.
The purpose of life is seen as the survival of the
species, the transmission of our genes to the
next generation.
Parental Investment
Because of biological differences (“the cheap
sperm and precious egg”), men and women
have different parental investments in the
transmission of their genes to their offspring, and
that is why they have evolved differently in terms
of mate selection.
Note “lonely hearts” studies. How do men and
women market themselves in order to attract a
mate, and what are they’re looking for in a
potential partner?
Gender Differences in Mate Selection
Men prefer youth and beauty, because these
indirectly mean health and fertility.
Women prefer ambition, resources in a man.
Since their parental investment is larger than the
man’s, they contribute their “precious egg”,
women need to guarantee (not in the personal
sense, but in the sense of the species) that their
relatively few offspring will be protected while
they gestate, give birth, and nurse.
Note cross-cultural studies showing that men in
different cultures all over the world prefer youth
and beauty in a mate.
He wants youth and beauty she wants resources
She has youth and beauty he has money