The Nature and Nurture of Behavior

1
The Nature and Nurture of Behavior

• Module 5
• Genetic Influence of Behavior

2
Genes Our Biological Blueprint

• Every cell nucleus in our bodies contains
  chromosomes (23 inherited from the mother, 23
  from the father).
• Consist of genes, which are a segment of DNA
  (deoxyribonucleic acid).
• 98 of our genetic sequence matches that of
  chimps, and 99.9 matches that of all other
  humans.

3
Evolutionary Psychology

• When certain traits are selected, they will
  eventually come to prevail.
• Natural selection may explain many human traits.
• Since the beginning of human history nature has
  selected the traits of those best suited to
  survive.
• This explains why we are so similar and the
  phenomena such as why infants fear strangers, and
  why parents are devoted to children (see p. 89).

4
Sexuality

• We exhibit gender differences.
• Males have a more recreational attitude toward
  sex compared to women (p. 89).
• Evolutionary psychologists explain this Women
  incubate and nurse one infant, males spread genes
  by impregnating females.
• Evolutionary psychologist say that men are drawn
  to healthy, fertile women who will pass on their
  genes.

5

• Women are attracted to men who are mature,
  dominant, and affluent, ie., show the capacity to
  support and protect.
• Nature selects behavioral tendencies that
  increase the likelihood of passing on their
  genes.
• Wouldnt it be even more advantageous if fathers
  were committed and bonded to one female?
• Cultural expectations bend gender behavior.

6

• Males can be socialized to be promiscuous or
  monogamous.
• Women show a great deal of variability.
• Evolutionary psychologists counter by saying that
  we have great capacity for learning.

7
Behavior Genetics Twin Studies

• How much do genetics and environment explain
  behavior?
• Identical Twins genetically identical.
• Fraternal Twins from different eggs. Like
  normal siblings.
• Identical twins are much more similar on
  extraversion, neuroticism, abilities and
  interests.
• Also have more similar social effects (eg.,
  divorce).

8

• Separated identical twins are more dissimilar
  than identical twins reared together, but more
  similar than fraternal twins reared apart.
• But, identical twins reared apart share the same
  prenatal environment. They share the same
  appearance, and tend to be reared in similar
  households.

9
Adoption Studies

• Adoptees share more traits with biological
  parents than with adoptive parents.
• Environmental factors shared by a familys
  children have virtually no impact on their
  personalities.

10
Temperament

• Refers to emotional excitability. Easy infants
  are relaxed and cheerful, difficult infants are
  irritable and intense. Temperament endures.
• Impulsive and emotionally reactive 3 year-olds
  develop into more impulsive and aggressive 21
  year-olds.
• Inhibited 3 year-olds become unassertive 18
  year-olds.
• Heredity overrides rearing in monkey temperament.

11
Heritability

• The proportion of variation among individuals
  that can be attributed to genes.
• If the heritability of height is 90, genetic
  influence can explain 90 of variation in height.
• Genetic influence can not explain gender
  differences or differences between race.
• It appears that nature enables nurture.
  Environment reacts to and shapes what nature
  predisposes.

12
Gene-Environment Interaction

• We cant say what percentage of an individuals
  personality is due to genes and what percentage
  is due to experience.
• There is a cascade of interactions between genes
  and environment. Our genes often affect how
  people react to and influence us.

13
Molecular Genetics

• Tries to identify specific genes that influence
  behavior.
• Most human traits are influenced by a combination
  of genes.
• Molecular geneticists are attempting to identify
  those at risk for genetic disorders such as
  Huntingtons Disease.
• May soon identify genes for depression,
  schizophrenia, alcoholism, sexual orientation,
  etc.