Identical twins tend to have similar personalities; if environment outweighs heredity in personality development, twins raised together should presumably have more similar personalities than those raised apart. A recent study of identical twins in both situations measured 11 key traits through a questionnaire, and concluded that 7 of the 11 are primarily products of heredity.
Which of the following, if established, would cast the most doubt on the study’s results?
(A) Fewer than half of the pairs of twins studied were raised separately.
(B) The ages of all of the twins studied fell within a 10-year range.
(C) Some of the traits that the study attributed to heredity developed in the separately raised twins because those pairs all grew up in similar families.
(D) Although over half the traits measured were determined to be linked to heredity, the nature of those traits varied widely.
(E) The 11 traits that were measured constitute a representative sample of larger, generally accepted pool of key personality traits