What is the moral basis of the authority of family members to act as surrogates for incompetent patients?

... The authority of family members should be understood as presumptive; that is, there is a moral presumption that a close family member should serve as surrogate for an incompetent patient. That presumption can be overcome or rebutted in a particular case, either when there is sufficient evidence that the usual reasons supporting this presumption do not hold or when the surrogate's decision exceeds appropriate limits of surrogates' decision-making discretion. In order to clarify these hard cases and appropriate public policy, we need a much deeper and more complex analysis than either the conventional view, or the alternative account that Pearlman and colleagues provide. I have sought here only to point toward some of the other grounds that a full account of family members' authority as surrogates would have to develop and explore in much more detail....