The longevity of humanity is measured in years remaining until extinction, and the longevity of individuals is measured as years of life expectancy.
Threats to the survival of our species can be measured in terms of three variables: uncontrollability, unavoidability, and extinction time. Uncontrollability is the extent that humans cannot influence the source of a threat. Unavoidability is the extent that humans cannot escape the threat. If uncontrollability and unavoidability are expressed as probabilities, then the probability of extinction is the result of multiplying them together. Extinction time is the time remaining from the present before the threat totally assures our extinction. Dividing the extinction time by the probability of extinction results in a number, in years, that expresses the longevity associated with the threat. Our goal when dealing with a threat is to maximize this “survival time.”
Threats to individual survival can be measured in a similar way. Just substitute “death” for “extinction.”
Since the shortest survival time is equal to longevity, any strategy to maximize it must include identifying all threats and decreasing uncontrollability and unavoidability for those with the shortest extinction or death times.