A large-scale study on the development of attention-deficit/hyperactivity disorder (ADHD) finds the following: The likelihood of both fraternal twins (who share about 50% of their genes) having the disorder is significantly lower than for identical twins (who share 100% of their genes). Furthermore, the likelihood for fraternal twins is only slightly higher than the likelihood of two non-related adoptive siblings raised in the same home both having the disorder. What is the most logical conclusi

A large-scale study follows two groups of children from birth: Group A consists of children raised by their biological parents, and Group B consists of children who were adopted at birth and raised by genetically unrelated parents. The study finds that the prevalence of a specific neurodevelopmental disorder is virtually identical between both groups. What is the most logical conclusion that can be drawn from this finding regarding the development of the disorder?