LO #10: With reference to relevant research studies, to what extent does genetics influence behavior?

Background Info: Behavioral Genetics Builds on what we know about the differences between species and applies these concepts to studying humans. Deals with understanding how both genetics and the environment contribute to human behavior.

Genes Located in the nucleus of each human cell. Hereditary units composed of a sequence of DNA. Hold the info needed to create the proteins required by all types of living creatures. These proteins determine how the organism looks and behaves.

Genome Projects All the genes have been identified for humans, chimpanzees and macaque monkeys. Role of specific genes in specific behavior remains unknown. Chimpanzees share 98% of the same DNA as humans. Macaque monkeys share 93%

How animal genetics applies to understanding human behavior Researchers can now triangulate to learn what genes primates share and what genes are uniquely human. It’s likely that many differences between man and closely related primates lie NOT in gene sequence but in the regulation of the expression of those genes. Animal research can be conducted to identify genetic influences on behavior and can possibly generalize to humans.

Genetic Predisposition Behavior will not be manifested without appropriate environmental stimuli. Diathesis-stress model: Used to explain the origin of depression Argues that depression is the result of a “genetic vulnerability” and traumatic environmental stimuli in early childhood. Some children don’t become depressed after a traumatic experience, whereas siblings do. Demonstrates no single cause-and-effect relationship between genes and behavior.

How studies show evidence of a Genetic Basis for Behavior 1. The studies try to determine the extent of genetic influence on particular behavior 2.They show correlations between behaviors and genetic inheritance. 3.If the heritability of a behavior is high, then individuals who share more genes should have high concordance rates for a behavior (shown in twin studies)

4. In MZ studies (identical twins): 100% of the genes are the same, so any difference in behavior is attributed to the environment. 5. In adoption studies, researchers can conclude that the common behaviors are attributed to the environment, since they do not share the same genes.

Inheritance of Intelligence

Bouchard & McGue (1981) Meta-Analysis Study Compiled data from 111 studies of IQ correlation Examined identical twins-reared apart for 100% genetic relationship baseline Results-found that the closer the kinship, the higher the correlation for IQ Concluded-any similarities are attributed to genetics

Minnesota Twin Study -longitudinal Bouchard et al Compared intelligence and other factors between self-selected sample of MZs reared together vs apart

Minnesota twin study cont. Results: Same person tested twice = 87% Identical twins reared together = 86% Identical twins reared apart = 76% Fraternal twins reared together = 55% Biological siblings reared together = 47% Conclusions: Heritability estimate for IQ is 70% with only 30% due to environmental factors.

Evaluation: Pros High ecological validity-participants from around the world Mean age=41, NOT adolescents Huge sample size

Evaluation : Cons Ethical concerns on how he reunited the twins No control of frequency of contact b/n twins prior to study Can’t assume twins raised together experience the same environment (equal environment assumption) All twins were white, from industrialized middle-class.

Scarr & Weinberg (1977) Horn et al. (1979) Challenged the criticism of “equal environment assumption” Compared IQ of adopted children and natural children Adopted children were from poor, lower class, lower IQ parents and were adopted by parents who were wealthy, white, middle class, with a high IQ. Assumptions: children have the same upbringing, same environment, same parents

Continued Differences in IQ should be attributed to genes Results: no difference in IQs Conclusions: environment has a stronger impact on IQ than previously believed. Supported the assumption that these children are in an equal environment.

Wahlstein (1997) Adoption studies in France Infants from low SES families went to high SES families Results: IQ score increased points in childhood Conclusions: an enriched environment may increase IQ in children It is likely that there is a strong interaction between genes and the environment

Factors to consider about intelligence Intelligence is difficult to define and measure IQ concordance rates between parents and children increase over time, which suggests that possibly children choose similar environments as their parents increasing the similarity of IQ Average IQ score is increasing-possibly due to exposure to changes in technology and environmental demands compared to years before-again supporting the role of environment on IQ

Limitation of holding genes responsible for behavior Genes are inherited but are not typically directly responsible for behavior. There is no single cause and effect relationship between genes and behavior. Role of specific genes in specific behaviors remains unknown.

Genes direct involvement Williams Syndrome Parents have a 50% chance of transmitting this disorder to their offspring Caused by a micro-deletion on the long arm of chromosome 7s Behaviors: strengths in recognizing faces, expressing themselves verbally, and musical talent. Weaknesses: visual-spatial construction tasks, high rates of anxiety and phobias.