Behavior Genetics

Predicting Differences Why are you the unique way you are? While you are unique, you are also very similar to others. Develop language Feel hunger Major physical features Feel drawn to produce & protect offspring Looks Sound Personality Interests Cultural & family background

Predicting Differences What causes our diversity, and our shared human nature? How much is attributed to environment? How much is attributed to our genes? These are questions of behavior genetics: The study of the relative power and limits of genetic and environmental influences on behavior.

Nature vs. Nurture Nature: The influence of our DNA that directs the inherited traits that influence our Nurture: The influence of the environment on our personality, physical growth, intellectual growth, and social interactions. personality, physical growth, intellectual growth, and social interactions.

Let’s look at nature influences Nature vs. Nurture Let’s look at nature influences

A Little About Genes 46 Chromosomes, 23 from each parent Each chromosome is made of a coiled chain of DNA Genes segments of DNA located on chromosomes transmit all heredity traits

A Little About Genes Genetically speaking, every other human being is your twin. Your DNA is 99.9% the same as the person sitting next to you. Humans and chimpanzees share about 96% of our DNA sequence. How much difference does that 4% make?

A Little About Genes Most of our traits are influenced by many genes. How tall you are The size of your vertebrae, leg bones, etc. Traits such as intelligence, happiness, aggressiveness are similarly influenced by groups of genes.

Adoption & Twin Studies Identical Twins Single egg that splits Genetically identical Don’t always have the same number of copies of those genes Fraternal Twins Separate eggs Genetically similar, as ordinary brothers & sisters

Adoption & Twin Studies Are identical twins behaviorally similar? Studies on personality traits of extraversion & neurotic scales show they are more similar than fraternal twins Social traits? 1500 same-sex, middle-ages twins divorce rates studied When a fraternal twin divorced, other was 1.6 times more likely to divorce than twins who didn’t divorce. Identical twin divorced resulted in other being 5.5 times more likely to divorce. Differing divorce risk about 50% attributable to genetics.

Separated Twins Twins separated at birth but raised in different homes have more traits of biological parents than adoptive parents. Anecdotal stories of Identical twins separated at birth with amazing similarities. The Jim Twins

Environmental Influence Study by comparing biological relatives and environmental relatives Personalities of biological relatives are as diverse as non-related people While adopted children are more like their biological parents, most adopted children benefit greatly from the environment of their home. Bottom line: Environment affects genetic predisposition

Heritability Heredity and heritability are different. Heredity is the percentage or proportion of a trait that is inherited. Heritability is the proportion of variation among individuals that are attributed to their differing genes. Heritability is the extent to which differences among people are attributed to genes.

Heritability Mark Twain suggested raising boys in barrels until age 12, feeding through a knot-hole. Boys would emerge with lower-than-average IQ scores because of their environment. Because of the similar environment, test score differences would be attributed to heredity. Heritability, the differences due to genes, would be near 100%

Heritability As environments become more similar, heritability as a source of differences becomes more important. If all people had very similar heredities, but were raised in different environments, heritability would be much lower.

Gene-Environment Interaction Imagine two babies: one predisposed to be attractive, social & easy going, the other not so much. First baby attracts more affectionate & stimulating care Develops into a warmer and more outgoing person Seeks activities & friends that further social confidence.

Gene-Environment Interaction Certain types of environments trigger genetic expression. Genes have the potential to influence development, environmental factors switch them on or off.

Gene-Environment Interaction Genes are self-regulating They react rather than lead the way. Genes and the environment work together like two hands clapping. They interact.

Nature vs. Nurture is the wrong way to look at behavioral genetics Nature vs. Nurture is the wrong way to look at behavioral genetics. Instead think of it as Nature via Nurture