Case studies: Falconer Model, Kendler etc al. (2016), Transracial Adoption Studies
This chapter is about chromosomes, the nature vs nurture debate, primarily done by studying the behavior of genetically similar twins to understand the extent of genetic influences vs environmental factors.
In each cell, we have 23 pairs of chromosomes, totaling 46 chromosomes. Chromosomes are like tiny packages inside the cells of our bodies. This thread-like structure each carrying a special code called DNA, made up of 4 chemical bases which determine our unique genetic code.
Genotype is the combination of genes you inherit from your parents, while your phenotype is what you actually look like and how you behave. So, while your genes might say you have the potential for certain traits, how they actually show up depends on a mix of genetics and other factors, like your environment.
Scientists study how genes affect behavior using different methods—looking at twins, families, and adopted children. These studies help us understand how much of our behavior is influenced by our genes and how much comes from our surroundings. Niche-picking is another way genes can affect us, where our genetic tendencies lead us to choose certain environments or lifestyles.
Falconer Model
Falconer’s model aims to explain twin heritability, suggesting that one’s phenotype is influenced by genetics, shared environment (like schooling and books), and individual environment.
It is a statistical method used in quantitative genetics to estimate the heritability of a trait within a population. It’s based on comparing the resemblance between relatives with the degree of their genetic relatedness.
This would assume that identical twins reared together have a higher IQ
correlation than identical twins reared apart, however, research shows that these twins do not have perfect correlation. According to the model, intelligence is only 54% inherited.
| Strengths | Weaknesses |
| – Quantitative Analysis: It provides a quantitative framework for studying the heritability of psychological traits, allowing numerical/ objective data – Predictive Power: Understanding the heritability of psychological traits helps in forecasting the likelihood of certain traits or behaviors manifesting in individuals based on their genetic background – Research Design: Provides a structured approach for conducting family, twin, or adoption studies to tease apart genetic and environmental influences | – Ignores “niche-picking,” where genetic predisposition leads individuals to select specific environments, impacting their behavior – Some twins weren’t separated immediately after birth, experiencing formative months together, making it hard to class them as being reared apart – Twin pairs, even when separated, often grew up in similar cultural and socioeconomic environments, not randomly allocated – Twins might not represent the broader population as desired, affecting the model’s generalizability |
Kendler et al. (2015)
Twin studies challenge the idea that IQ is solely genetic.
Kendler et al. (2015) found IQ can change based on environment, not just genetics. They studied 436 Swedish brothers, some raised by biological parents and some by adoptive parents. Those in better circumstances had a 4.4 point IQ boost by age 18.
Transracial Adoption Study
The Transracial Adoption Study, conducted in Minnesota later corroborated findings by Kendler. The study examined the IQ test scores of 130 black/ interracial children adopted by advantaged white families had higher IQs, especially if adopted early.
Yet, IQ correlation between adopted and biological siblings was high, suggesting environment matters. However, adopted children’s IQs were more like their biological parents’, indicating environmental influence. Another study found no IQ correlation in adopted siblings raised together, suggesting they seek their own paths.
Read here for more on the Case Studies in the Biological Approach to Behavior