The key to short-term energy storage in every living organism on Earth thus is found in the charge repulsions on small polyphosphate ions of ATP. Because of this universality of ATP, it has been suggested that ATP hydrolysis is one of the oldest chemical reactions of living organisms. By this hypothesis, one of the first steps toward life would have been the acquisition of energy for synthetic or metabolic purposes by the degradation of naturally occurring ATP or other polyphosphates in the surrounding ocean. (Even today, some bacteria store energy in the form of small inclusions of polyphosphates within their cell fluid.) All of the other energy-extracting and energy-storing machinery would have evolved later to keep these ATP-using reactions going in the face of shortages of natural ATP.

In comparison with nitrogen and phosphorus, the other Group VA elements - arsenic, antimony, and bismuth - are of lesser importance. One of the reasons for the poisonous character of many arsenic compounds is that arsenic can almost, but not quite, mimic the chemical behavior of phosphorus. It can substitute for phosphorus in certain compounds, but then is unable to function as phosphorus can, with lethal consequences. Arsenic lies on the borderline between nonmetals and metals. Antimony and bismuth both are metals of relatively little use except in some alloys used in making metal type because they expand upon solidifying.