A pathologist or any licensed physician or surgeon may conduct a postmortem examination on a dead human body when consent thereto is given in writing by the person prior to his death or when consent thereto is given by the spouse of the deceased; but if the spouse at the time of death was living apart from the deceased, or, if there is no spouse surviving, the consent thereto may be given by whichever one of the next of kin, as determined by law of this State, assumes custody of the body for burial purposes provided that the autopsy shall not be performed under a consent given by such person if, before the autopsy is performed, any other next of kin shall object in writing to the person by whom the autopsy is to be performed. If two or more persons assume custody of the body, consent of one of them shall be deemed sufficient. In the event no next of kin assumes custody of the body for burial purposes, consent may be given by the person who assumes custody of the body for burial. In the event all of the next of kin are minors, the consent of any minor who shall have reached the age of sixteen shall be sufficient. Any consent purporting to have been given by a person authorized to give consent shall be conclusively presumed to have been given by the person.