Behavior Genetics in Psychology

Apologies for previous scheduling issues causing delays in the talk.
Discussing the third bucket in a series, focusing on behavior genetics.
Previous approaches included sociobiological/evolutionary psychology and molecular end.
Sociobiological approach assumed behavior follows certain rules of evolution, with predictions based on heritability and evolution.
Molecular end approach examined evolutionary change at the DNA level, supporting punctuated equilibrium.
Behavior genetics focuses on behavior in a heritable context, with debates about its validity.
Criticisms of behavior genetics include oversimplification and reliance on outdated assumptions.
Behavior geneticists look for patterns of shared traits among related individuals to infer genetic influences.
Universal traits in species do not necessarily have genetic basis.
Behavioral traits that run in families do not necessarily have genetic causes, as environment also plays a role.
Identical twins share 100% of their genes, while fraternal twins share 50%, making it a popular approach to infer genetic influences.
However, this approach is flawed as identical twins are not always raised in identical environments, and dizygotic twins often have different environments.- Monozygotic twins can have different placenta development depending on when they split during fetal life
If the split occurs within the first five days, each twin gets their own placenta (monochorionic pregnancy)
If the split occurs between days five and ten, they share a placenta (bichorionic pregnancy)
In monochorionic pregnancies, the fetuses share a blood stream to a greater extent than in bichorionic pregnancies
Monochorionic twins have more similar IQs than bichorionic twins
Marmoset monkeys provide an example of the differences in blood flow between twins
Sex differences in behavior and environment can be observed from infancy
A study in the 1980s by Benbow and Stanley Molenaar found significant differences in average IQs between boys and girls, and a higher ratio of boys in the highest IQ range
The study was criticized for ignoring the environmental differences between boys and girls, such as their differential treatment by teachers and parents
Adoption studies are used to examine patterns of shared traits in individuals raised in the same environment but with different genetic makeup
Seymour Kety's landmark study in the late 1960s and early 1970s used Danish adoption records to identify cases of schizophrenia and determine the likelihood of the trait being passed on genetically or environmentally
Kety found that the incidence of schizophrenia was higher in adoptees with a biological parent with the disease than in those without, and higher still in those with an adoptive parent with schizophrenia
The study provided evidence for a genetic component to schizophrenia and set the standard for behavioral genetic studies.
Problems with the adoption study approach include the difficulty of controlling for postnatal shared environment and prenatal effects.- The text discusses issues with behavior genetics research, specifically using adoption and identical twins separated at birth as approaches.
Adoption approach:
- High rates of paternity uncertainty can make genetic studies complicated.
- Adoptive placements are not random, which can affect the results.
Identical twins separated at birth approach:
- Identical twins separated at birth and reunited in adulthood have been studied extensively.
- Researchers have found various similarities between the twins, but challenges exist due to non-random placement in families and small sample size.
Environmental effects prenatally have significant influence:
- Hormonal environment in the womb can impact fetal development.
- Maternal age at birth can influence the age of puberty onset in offspring.
Prenatal stress can lead to long-term effects:
- Exposure to stress hormones in the womb can have lifelong consequences, such as smaller brain size, thinner cortex, and cognitive decline.
Researcher's observation of non-Mendelian inheritance of traits:
- A trait that is not genetic can be inherited through the prenatal environment.
Nutrients in the mother's bloodstream:
- A fetus learns about the nutritional availability in its environment through the mother's circulation.
Dutch Hunger Winter:
- During the winter of 1944 in Holland, the Nazis diverted all food to Germany, causing famine.
- A third-trimester fetus during this period learned that food availability was low.
Conclusion:
- The text highlights the importance of considering prenatal influences on offspring's development and the limitations of focusing solely on genetic factors.