A New Metric of Inclusive Fitness Predicts the Human Mortality Profile

Abstract

Biological species have evolved characteristic patterns of age-specific mortality across their life spans. If these mortality profiles are shaped by natural selection they should reflect underlying variation in the fitness effect of mortality with age. Direct fitness models, however, do not accurately predict the mortality profiles of many species. For several species, including humans, mortality rates vary considerably before and after reproductive ages, during life-stages when no variation in direct fitness is possible. Variation in mortality rates at these ages may reflect indirect effects of natural selection acting through kin. To test this possibility we developed a new two-variable measure of inclusive fitness, which we term the extended genomic output or EGO. Using EGO, we estimate the inclusive fitness effect of mortality at different ages in a small hunter-gatherer population with a typical human mortality profile. EGO in this population predicts 90% of the variation in age-specific mortality. This result represents the first empirical measurement of inclusive fitness of a trait in any species. It shows that the pattern of human survival can largely be explained by variation in the inclusive fitness cost of mortality at different ages. More generally, our approach can be used to estimate the inclusive fitness of any trait or genotype from population data on birth dates and relatedness.

Individuals’ expected genetic contributions to future generations, reproductive value, and short-term metrics of fitness in free-living song sparrows (Melospiza melodia)

“…Rather, further direct consideration of the structure of individual pedigrees and genealogies and hence V i might provide useful complementary insights into evolutionary outcomes, including age‐ and sex‐structured contributions, lineage introgression, individuals responsible for inbreeding, and ultimately inclusive fitness (e.g., Caballero and Toro ; Suwanlee et al. ; Barton and Etheridge ; Newman and Easteal ).…”

“…Because individual V i represents the outcome of genetic and environmental effects acting across multiple generations, it should not generally be directly treated as a focal trait in quantitative genetic analysis. Rather, further direct consideration of the structure of individual pedigrees and genealogies and hence V i might provide useful complementary insights into evolutionary outcomes, including age-and sex-structured contributions, lineage introgression, individuals responsible for inbreeding, and ultimately inclusive fitness (e.g., Caballero and Toro 2000;Suwanlee et al 2007; Barton and Etheridge 2011;Newman and Easteal 2015).…”

Individuals’ expected genetic contributions to future generations, reproductive value, and short-term metrics of fitness in free-living song sparrows (Melospiza melodia)

“…Further consideration of the structure of individual pedigrees and genealogies and hence the basis of V i might then provide useful complementary insights into age-specific contributions, lineage introgression, individuals responsible for inbreeding, and ultimately inclusive fitness (e.g. Caballero & Toro 2000; Suwanlee et al 2007; Barton & Etheridge 2011; Newman & Easteal 2015).…”