Genes strongly influence life span as witnessed by the almost one-million fold difference between species in their maximum life spans. Yet, within most species, individuals vary widely in life expectancy. In social insects, the same genome can be programmed during development for either a short-lived worker that lives no longer than a fruit fly, or a queen that lives longer than a mouse. Less extreme variations in life histories are observed in many other species, in response to variations in the external environment during development. Another dimension is the variations that cannot be attributed to the external environment, such as shown by laboratory round worms which are totally inbred and reared in a liquid culture that equalizes the environment. Yet, worms, like inbred mice or identical twins, vary widely between individuals in their life spans. Explanation of these 'intrinsic' variations requires consideration of random events during development that are not under strict genetic control. We may anticipate that details of the human genome will only go so far in identifying origins of human individuality at any stage of life.