A pathologist or a licensed physician or surgeon may conduct a postmortem examination on a dead human body when consent is given in writing by the person prior to his death or when consent 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 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; however, the autopsy must not be performed under a consent given by a person if, before the autopsy is performed, any other next of kin objects 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 is sufficient. If 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. If all of the next of kin are minors, the consent of a minor who is sixteen years of age or older is sufficient. A consent purporting to have been given by a person authorized to give consent is conclusively presumed to have been given by the person.