Necessary, because if it were not true — if standard personality tests MIGHT NOT detect birth-order effects on personality even if those effects exist — then the fact that studies using standard personality tests have not found birth-order effects would not establish that those effects do not exist. In other words, the negation of (A) opens the possibility that the effects DO exist, despite the failure of studies based on standard personality tests to prove their existence.

Not necessary, because the argument doesn’t depend on any comparison between how people behave with family than with non-family. Even if people behave very similarly, that doesn’t change how we interpret any of the birth-order studies cited and it doesn’t change whether those studies provide evidence of the lack of birth order effects.

Not necessary, because even if family members’ perceptions of a person’s personality do tend to change as that person grows up, that doesn’t suggest that birth-order might have some effect on personality. There could still be no actual effect on personality, only an effect on how family members’ perceive the person’s behavior.

Not necessary, because the conclusion concerns whether birth order has a “lasting” effect on personality. Whether there might be some detectable effect in young children doesn’t change that fact that we have evidence that these effects do not exist among adults.

Not necessary, because birth order can still impact how a person’s behavior is perceived, even of those perceptions are not accurate. For example, family members might perceive a sibling has getting angry whenever he’s served last at dinner; in reality the sibling might not get angry every time he’s served last. Regardless of the reality, the family members have a certain perception and that perception can be influenced by the person’s birth order.