General Psychology

Scripture

• Matthew 5:9Blessed are the peacemakers, for they will be

called children of God. .

Those who strive to prevent contention, and strife, and war. Who use their influence to reconcile opposing parties, and to prevent hostilities, in families and neighborhoods. Every man may do something of this; and no man is more like God than he who does it.

Thanks for Everything Dad

Overview: Nature/Nurture/Diversity Questions

How do we explain traits that all humans may have in common?

How do we explain the origins of diversity, the source of differences in the traits:• between genders?• among cultures?• among individuals?

But first, how do we investigate these issues?

Behavior Genetics: Predicting Individual Differences

The topics in the text:1.genes2.twin and adoption studies 3.temperament and heredity4.molecular genetics5.heritability6.gene/environment interaction

Behavior geneticists study how heredity and environment

contribute to human differences.

Let’s start by looking at GENES.

Genes are parts of DNA molecules, which are found in chromosomes in the nuclei of cells.

DNA (Deoxyribonucleic Acid)

GENES:The Building Blocks of Heredity and Development

Chromosomes are made of DNA, which are made of genes.

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Chromosome: threadlike structure made largely of DNA

molecules

DNA: a spiraling, complex molecule containing

genes

Chromosomes and Inheritance The human genome includes 46

chromosomes in 23 sets matched sets; each chromosome has the same gene locations.

This includes the X and Y chromosomes, not a matched set in males, who are missing some genes on the Y.

A biological parent donates half his/her set of chromosomes to his/her offspring.

We received half a set of chromosomes from each biological parent.

The Human Genome:20,000 to 25,000 Genes

Human genomes are so nearly identical that we can speak of one universal human genome.

Yet tiny genetic differences make a difference. If there is a: .001 percent difference in

genome, your DNA would not match the crime scene/you are not the baby’s father.

0.5 to 4 percent difference in genome, you may be a chimpanzee.

50 percent difference in genome, you may be a banana.

The genome: an organism’s entire

collection of genes

How Genes Work Genes are not blueprints;

they are molecules. These molecules have the

ability to direct the assembly of proteins that build the body.

This genetic protein assembly can be turned on and off by the environment, or by other genes.

Any trait we see is a result of the complex interactions of many genes and countless other molecules.

Or vary the genes in the same environment?

Next step for behavior geneticists:Controlling Variables

Can we design an experiment to keep genes

constant and vary the environment and see what

happens?

Twin and Adoption StudiesTo assess the impact of nature and nurture, how do we examine how genes make a difference within the same environment?study traits of siblings vs. identical twins see if the siblings vary more than twins

Fraternal and Identical TwinsFraternal “twins” from separate eggs are not any more genetically alike than other siblings.

Identical twin: Same sex only

Fraternal twin: Same or opposite sex

Twin and Adoption StudiesHow do we find out how the same genes express themselves in different environments?We can study the traits of identical twins as they grow up, or if they were raised separately (e.g., the Minnesota Twin Family Study).

Identical vs. Fraternal TwinsStudies of twins in adulthood show that identical twins are more alike than fraternal twins in:personality traits such as extraversion (sociability) and neuroticism (emotional instability).behaviors/outcomes such as the rate of divorce.abilities such as overall Intelligence test scores.

Critiques of Twin Studies1.In the more recent years of the Minnesota Twin Family Study, twins have known about each other and may influence each other to be more similar.2.Coincidences happen; some randomly chosen pairs of people will have similar traits, including even spouses, children, and dogs with identical names.3.Environments may be similar; adoptive families tend to be more similar than randomly selected families in education, income, and values.

Studies of Identical Twins Raised ApartSimilarities found in identical twins despite being raised in different homes:personality, styles of thinking and relatingabilities/intelligence test scoresattitudesinterests, tastesspecific fearsbrain waves, heart rate

BUT none of these factors explains, better than the genetic explanation, why fraternal twins have more differences than identical twins.

Searching for Parenting Effects:Biological vs. Adoptive RelativesStudies have been performed with adopted children for whom the biological relatives are known.

Findings: Adopted children seem to be more similar to their genetic relatives than their environmental/nurture relatives.

Given the evidence of genetic impact on how a person turns out,

does parenting/nurture make any difference?

Does the home environment have any impact?

Despite the strong impact of genetics on personality, parenting has an influence on:

religious beliefs values manners attitudes politics habits

Parenting Does Matter

If parenting has an influence, why are siblings so different? Siblings only share half their genes. Genetic differences become amplified as people react to

them differently. Siblings are raised in slightly different families; the youngest

has more older siblings and has older (wiser? more tired?) parents.

Temperament is another difference not caused by parenting.

From infancy into adulthood, most people do not seem to change temperament (defined as a person’s general level and style of emotional reactivity).

According to some researchers, three general types of temperament appear in infancy:• “easy”• “difficult”• “slow to warm up”

Molecular Genetics

Molecular genetics is the study of the molecular structure and function of genes. Molecular genetics might help us see exactly how specific genes have an influence on behavior. Genetic tests can reveal which people are at risk for many physical diseases, and may soon identify people at risk of mental health disorders. Ethical conundrum: should people use genetic tests to select sperm, eggs, and even embryos?

Clarifying Heritability If five unrelated people had nearly identical upbringing, but differed in a trait such as shyness, then the heritability of this trait for them is close to 100 percent. Nurture may have influenced how shy they are, but because it influenced them all in the same way, any differences are almost certainly caused by genes.

Heritability When you see a variation

of some trait within a population, the heritability of that trait is the amount of variation in the population that is explained by genetic factors.

This DOES NOT tell us the proportion that genes contribute to the trait for any one person.

The heritability of a trait also does not tell us whether genetics explain differences between groups/populations.

Nature and nurture working togetherInteraction of Genes and Environment Some traits, such as the overall design of our bodies, are set by

genes. Other traits, such as physical and mental abilities, develop in

response to experience.How does the interaction of genes and environment work?

Genetic traits influence the social environment, which in turn affects behavior.

Evolutionary Psychology: Natural Selection: How it Works