Have human biological functions evolved in support of a life-span?

Published data on age-related human biological functions are surveyed. For the many showing a linear decrease, regressions were calculated, or existing functions extrapolated, to yield an intercept on the abscissa. The values of chi(0), the age at which a function ceases, provide a tentative common means of comparison. The distribution of chi(0) is skewed because of the apparent longevity of nervous and cerebral functions. The database is sufficiently large to enable one to distinguish those biological functions which appear to have immediate survival value from those which do not. Such an approach may link biomarkers to estimates of the life-span of species.