Man's beginning, like his seven ages, has always lacked sharp definition. Does life begin at conception, implantation, birth? Answers to this question have shaped attitudes toward such practical measures as contraception and abortion. By contrast, death always seemed to be clearly defined. Everyone knew that life ended when respiration stopped and the heart ceased beating. The fact that metabolic activity may have continued in nervous tissue for 15 minutes and in some organs for a few hours was of no practical consequence. Death was primarily a cardiac event.
With the advent of respirators and cardiac pacemakers, death lost sharpness of definition, acquiring some of the haziness which characterizes life's beginning. When a comatose patient can be maintained on a respirator for weeks after his brain has passed beyond possible recovery, cessation of spontaneous breathing and heartbeat no longer provide reliable end-points. Clearly, death must be redefined in other terms.