The best evidence supporting the role of genetic factors in intelligence is provided by studies that compare

A) children to both their biological and adoptive parents.
B) identical and fraternal twins.
C) people born in different generations since the 1930s.
D) children raised in poverty and middle-class children.

Studies that compare identical and fraternal twins provide the best evidence supporting the role of genetic factors in intelligence. This is because identical twins share 100% of their genes while fraternal twins share only 50% on average, making it easier to differentiate between genetic and environmental influences on intelligence. Studies with adoptive families, such as choice A, provide evidence for the role of environment, but do not necessarily isolate genetic factors. The choices C and D are not relevant to studying genetics and intelligence.