Developmental Axioms in Life History Evolution

Life history theory is often invoked to make universal predictions about phenotypic evolution. For example, it is conventional wisdom that organisms should evolve older ages at first reproduction if they have longer lifespans. We clarify that life history theory does not currently provide such universal predictions about phenotypic diversity. Using the classic Euler-Lotka model of adaptive life history evolution, we demonstrate how predictions about optimal age at first reproduction depend on rarely acknowledged, prior theoretical assumptions (i.e., axioms) about organismal development. These developmental axioms include the rates, forms, and tradeoffs that relate to growth or differentiation. Developmental innovations transform the biology underlying these axioms. Consequently, Euler-Lotka and related life history models do not make coherent predictions at macroevolutionary scales, where developmental innovations occur (e.g., across mammals, birds, or insects). By focusing on historical innovations instead of universal rules, life history theory can reconnect with flourishing research in evolutionary developmental biology.