Behavior Genetics

Predicting Differences You are unique, but also very similar to others. Looks Sound Personality Interests Cultural & family background Develop language Feel hunger Major physical features Feel drawn to produce & protect offspring

Predicting Differences What causes our diversity, and our shared human nature? How much is attributed to environment? How much is attributed to our genes? The nature/nurture argument

Nature vs. Nurture Nature - the influence of our DNA that dictates the inherited characteristics that influence our personality, physical growth, intellectual growth, and social interactions. Nurture - the influence of the environment on personality, physical growth, intellectual growth, and social interactions.

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 identical 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 face, 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? – More similar on extraversion & neurotic scales 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. Most adopted children benefit greatly from the environment of their home. – Environment affects genetic predisposition

Heritability Heritability is the proportion of variation among individuals that are attributed to their differing genes. It is not the percentage or proportion of a trait that is inherited. It 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 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, heredity 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 Genes are self-regulating – They react rather than lead the way. Genes and the environment work together like two hands clapping. They interact.

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.

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