Twin studies have long been used to separate genetic from environmental influences on traits. Identical twins share all genes, while fraternal twins share about half, so greater similarity between identical twins suggests genetic influence. However, identical twins may also be treated more similarly by parents and teachers, potentially confounding genetic and environmental effects. Researchers now supplement twin studies with molecular genetics to address these limitations.
It can be inferred from the text that
twin studies have provided no useful information about genetics
identical twins are always treated exactly like fraternal twins
environmental factors have no influence on human traits
research methodologies may have limitations that require complementary approaches to address
Correct Answer: D
Choice D is the best answer. Twin studies have limitations; molecular genetics supplements them.
- Context clues: Confounding effects are a limitation; researchers "now supplement" with other methods.
- Meaning: Combining approaches addresses what one method alone can't.
- Verify: The addition of molecular genetics shows recognition of twin study limitations.
💡 Strategy: When new methods are added to address limitations of old ones, infer the value of complementary approaches.
Choice A is incorrect because twin studies have been useful; they have limitations, not uselessness. Choice B is incorrect because the passage says identical twins "may also be treated more similarly." Choice C is incorrect because environment is considered a factor that confounds interpretation.