Figure 1.

(a) The demographic parameters for a hypothetical non-senescing population, as imagined by Hamilton (1966). Age-specific survival is constant, and cumulative survival declines geometrically. Age-specific reproduction rates are constant after the age of first reproduction, which in this case is age-class 12. (b) Hamilton's sensitivity functions, which reflect the strength of natural selection in the population described in (a). The symbols in the sensitivity functions represent terms from the discrete version of the Euler–Lotka equation, where r is the intrinsic rate of increase, l(x) is the probability of survival to age x, m(x) is the expected number of offspring produced by an individual of age x and T is a measure of generation time. (a) Dashed line, age-specific survival; black line, cumulative survival; grey line, age-specefic fecundity. (b) Black line, selection on survival; grey line, selection on fertility.