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A very simple mathematical exposition of reproductive value in an age- and sex-structured sexual diploid population employs reproductive value as the probability that a random gene in a distant generation traces its ancestry to a given individual or set of individuals today. Although the total reproductive values of all females and that of all males are not in general equal, but instead proportional to the average age of a new mother and a new father, respectively, Fisher׳s equal-investment conclusion for the sex ratio remains valid because the total reproductive value of age-zero females equals the total reproductive value of age-zero males. However, the conclusion is seen to require an extra assumption, namely stability of the age-distribution.

Original publication




Journal article


J Theor Biol

Publication Date





233 - 235


Diploidy, Equal investment, Overlapping generations, Sex ratio, Structured populations, Animals, Demography, Diploidy, Ecosystem, Female, Humans, Inheritance Patterns, Male, Models, Theoretical, Reproduction, Sex Ratio