What is the default action for infants?

Never mind infants, what about people of any age who are unconscious with hope of recovery, and those unconscious with some hope for recovery, and those unconscious with no medical hope for recovery? What is the "default choice" assuming the person has never expressed an opinion before? This would be infants and anyone who has never given much thought to the possibility they may be in this situation. This question must be answered by someone, either society or by someone whose decision society won't try to override. Perhaps a parent, perhaps a family member, perhaps a doctor, perhaps a committee, perhaps a parliament through lawmaking power. If there is no society-wide default, then each case will be decided by which person's arguments carry the day. This may boil down to who has the stronger personality, the person's family member or his doctor.