In a hypothetical study, psychologists found that, on a measured index of impulsiveness, there was a strong positive correlation between identical twins and a weaker positive correlation between fraternal twins.
They also found that, on an index of agreeableness, there was a strong positive correlation between identical twins that grew up together, and a weaker positive correlation between identical twins that were separated at birth and grew up apart.

Based on that study, we may conclude that impulsiveness is genetically determined , and agreeableness is partly genetically and partly environmentally determined.

Question

In a hypothetical study, psychologists found that, on a measured index of impulsiveness, there was a strong positive correlation between identical twins and a weaker positive correlation between fraternal twins.
They also found that, on an index of agreeableness, there was a strong positive correlation between identical twins that grew up together, and a weaker positive correlation between identical twins that were separated at birth and grew up apart.

Based on that study, we may conclude that impulsiveness is genetically determined , and agreeableness is partly genetically and partly environmentally determined.

BlackTom AI · Accepted Answer

Let’s parse what the study reports and how that translates to what is genetically determined versus environmentally influenced.
Option A: 'is genetically determined' for impulsiveness. The study shows a strong positive correlation between identical twins (who share essentially all their genes) on impulsiveness, and a weaker positive correlation for fraternal twins (who share about half their genes). This pattern is classic for a genetic influence: higher similarity when genes are more alike. Therefore, concluding that impulsiveness has a substantial genetic component is reasonable, though it does not mean that impulsiveness is wholly determined by genes; environment can still play a role.
Option B: 'is partly genetically and partly environmentally determined' for agreeableness. The results indicate a strong correlation for identical twins raised together and a weaker correlation for identical twins separated at birth and raised apart. This pattern suggests both genetic factors (the similarity between identical twins) and environmental factors (the reduced similarity when reared apart) contribute to agreeableness. It implies a genetic influence exists, but environmental conditions also shape this trait, leading to a partly genetic, partly environmental determination.
In a broader sense, these findings align with a common interpretation in behavioral genetics: traits can be influenced by genes to varying degrees, with environments moderating, amplifying, or mitigating those genetic effects. The strong twin correlations for impulsiveness among identical twins support a notable genetic component, while the pattern for agreeableness—heightened similarity when raised together but diminished when raised apart—points to both heritable influences and environmental shaping. 
Thus, Option A correctly reflects a genetic determination for impulsiveness, and Option B correctly reflects a partial genetic and partial environmental determination for agreeableness. 
Note: It’s important to recognize that 'genetically determined' does not imply gene-only control; it means genetic factors play a significant role. Similarly, 'partly genetically and partly environmentally determined' does not exclude genes from influencing the trait, but highlights substantial environmental contributions as well.

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