Chapter 2 Section 4: The Genetic Contribution

Nature/Nurture Debate How can heredity effect personality? – Genes are made up of elements of DNA & they form chemical codes for the synthesis of protein – The proteins affect virtually every aspect of the body – Genes affect personality through their effects on the brain & nervous system of an infant

Measured by 2 Ways Studying the temperament of infants & children By doing hereditability studies of twins & adopted individuals

Heredity & Temperament Infancy – Differ in activity level, mood, heart rate responsiveness, & attention span – Born with genetically determined temperaments Physiological dispositions to respond to the environment in certain ways Quite stable over time

Heredity & Traits Estimate the heritability of specific traits within a group of children or adults Favored by behavioral geneticists – An interdisciplinary field of study concerned with the genetic basis of behavior & personality Heritability: A statistical estimate of the proportion of the total variance in some trait that is attributable to genetic differences among individuals within a group.

Computing Heritability Look at adopted children Identical v. fraternal twins Identical twins reared apart

2-7 Twins Identical (Monozygotic) Twins: – Develop when a fertilized egg divides into 2 parts that develop into separate embryos Fraternal (Dizygotic) Twins: – Develop when two separate eggs are fertilized by different sperm – They are no more alike genetically than any other pair of siblings.

Twin Studies Studying identical twins separated near birth is one behavior genetic method Gerald and Mark met at age 31 after being separated at birth. Both are volunteer firefighters Like to hunt, eat Chinese food, and watch John Wayne movies Drink the same brand of beer, with their hands held the same way (pinky curled)

2-10 Evaluating Genetic Theories Reasons for Caution – Not all traits are equally heritable or unaffected by shared environment. – Some studies may underestimate the impact of the environment. – Even traits that are highly heritable are not rigidly fixed. Genetic predisposition does not imply inevitability