The Psychology of the Person Chapter 10 Biological Research

Naomi Wagner, Ph.D

Lecture Outlines Based on Burger, 8 th 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 Picture shows male identical twins

Fraternal twins share about 50% of their genes

They are formed when two different eggs are fertilized by two different sperm cells Picture shows two young children playing, a boy and a girl

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 Picture shows the actor from the House show

The study of extraversion introversion

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 Picture shows the young and beautiful Ann Nicole Smith and her old millionaire husband