Biological time value.
A measure of time value for living species, a natural discount rate, is proposed. It is the rate at which a species reveals its progressive disregard of the importance of future events. The discount rate is shown to be equal to the average (standard) metabolic rate for the species at a steady-state condition. The connection of the discount rate to standard empirical measures allows it to be assigned a numerical value. Knowing a species' discount rate should help determine its successional success and allow more meaningful solutions to optimality problems in biology.