General PsychologyChapter 4:

Nature, Nurture & Human Diversity

Sarah Rach-Sovich

Behavioral Geneticists

• Explore the genetic and environmental roots of human differences

• Weight the effects and interplay of heredity and environment

Genes: Our Codes for LifeChromosomes containing DNA

(deoxyribonucleic acid) are situated in the nucleus of a cell.

Segments within DNA consist of genes that make proteins to determine our development.

Genome is the set of complete instructions for making an organism,

containing all the genes in that organism. Thus, the human genome

makes us human, and the genome for drosophila makes it a common house

fly.

Even the person you like least is your near-clone, sharing about 99.9% of your

DNA

Twin & Adoption Studies

• Identical Twins develop from a single fertilized egg that splits in two. They are genetically identical.

• Fraternal Twins develop from separate fertilized eggs, share a fetal environment, but they are genetically no more similar than ordinary brothers and sisters

Biological Vs. Adoptive Relatives

Adoption studies, as opposed to twin studies, suggest that adoptees (who may be biologically unrelated) tend to be different from their adoptive parents and siblings.

Environmental factors shared by a family’s children have virtually no impact on their personalities.

Why are children in the same family, so different?

• Is it because each sibling experiences differing peer influences and life events?

• Is it because sibling relationships ricochet off each other, amplifying their differences?

• Is it because siblings - despite sharing half their genes - have very different combinations of genes and may evoke very different kinds of parenting?

So… Does parenting even matter?

• YES!• Parents do influence their

children's’:• Attitudes• Values• Manners• Faith• Politics

• Adoptive children have a good chance of thriving, especially when adopted as infants

Temperament & Heredity• Temperament refers to a person’s

stable emotional reactivity and intensity. • Reactive, intense, fidgety• Easygoing• Quiet• Placid

• Identical twins express similar temperaments, suggesting heredity predisposes temperament.

Nature & Nurture

• Genes are self-regulating • Genes react• Genes are part of the recipe, not

the finished food

Gene-Environment Interaction• Genes and experiences are both

important• They interact• Our genetically influenced traits

evoke significant responses in others

“Heredity deals the cards; environment plays the hand.”

Psychologist Charles L. Brewer

Evolutionary Psychologists

• Focus on mostly what makes us so much alike as humans

• Use the principles of natural selection to understand behaviors and mental processes

Natural Selection

• The principle that, among the range of inherited trait variations, those that lead to increased reproduction and survival will most likely be passed on to succeeding generations

• When certain traits are selected by conferring a reproductive advantage to an individual or species – those traits, over time, will prevail

Artificial Selection

• Biologists like Belyaev and Trut (1999) were able to artificially rear and domesticate wild foxes, selecting them for friendly traits.

• Any trait that is favored naturally or artificially spreads to future generations.

Gender Differences in Sexuality

SEX SEX SEX!!!

• Who desires more frequent sex?• Who thinks more about sex?• Who masturbates more often?• Who initiates more sex?• Who sacrifices more to gain sex?

Answer???

MEN MEN MEN!!!

Gender Differences in Sexuality

Question (summarized)

MaleFemale

Casual sex 58%34%

Sex for affection 25%48%

Think about sex everyday

54%19%

Males and females, to a large extent, behave and think similarly.

Differences in sexes arise in regards to reproductive behaviors.

Natural Selection & Mating Preferences

• Natural selection has caused males to send their genes into the future by mating with multiple females since males have lower costs involved.

• However, females select one mature and caring male because of the higher costs involved with pregnancy and nursing.

Mating Preferences• Males look for youthful appearing

females in order to pass their genes into the future. Females, on the other hand, look for maturity, dominance, affluence and boldness in males.

• Data is based on 37 cultures.