Extrinsic mortality is not the same as diminishing marginal returns on mortality reduction

Area of Science:

• Evolutionary biology
• Demography
• Human life history

Background:

• Selection pressures on survival vary significantly across different age groups.
• Reproductive effort (RE) models must account for age-specific mortality rates.
• Infant and adult mortality have distinct impacts on optimal life history strategies.

Purpose of the Study:

• To investigate how age-specific mortality influences selection on the human life cycle.
• To determine the relative importance of infant versus adult survival in shaping reproductive decisions.
• To highlight the necessity of age-specificity in demographic models of human reproduction.

Main Methods:

• Utilized an age-structured demographic model.
• Analyzed the effects of varying infant and adult mortality rates on selection.
• Simulated life cycle dynamics under different mortality scenarios.

Main Results:

• Infant mortality acts as a primary constraint on the human life cycle.
• Selection strongly favors investments in infant survival over adult survival.
• Age-specific effects are critical for accurately modeling human reproductive effort.

Conclusions:

• Infant survival is a key factor in human evolutionary trajectories.
• Reproductive strategies are significantly shaped by the differential impact of age-specific mortality.
• Future demographic models must incorporate age-specific selection pressures for comprehensive understanding.