Life history theory

Life history theory explains how organisms allocate limited resources among growth, survival, and reproduction, shaping traits such as age at maturity, lifespan, and offspring number.

Life history trade-off: A constraint in which investment in one biological function reduces resources available for another. Limited energy forces allocation choices among growth, survival, and reproduction.
Natural selection: Differential survival and reproduction cause heritable traits to become more or less common across generations. Selection favors allocation patterns that leave more descendants in particular environments.
r/K selection theory: A framework contrasting strategies associated with rapid reproduction and population growth with those associated with competitive environments near carrying capacity. This historical framework applies allocation ideas to broad contrasts in ecology.
Disposable soma theory: A theory proposing that organisms allocate limited resources between reproduction and maintaining the body, affecting aging and lifespan. It gives a specific allocation account of aging within broader life-history reasoning.
Age at first reproduction: The age at which an organism first produces offspring. Maturing earlier can increase reproductive opportunities while reducing time for growth.
Fitness (biology): An organism's contribution of descendants to future generations, often measured relative to others. Life-history traits matter through their effects on reproductive success.
Fast–slow continuum: A comparative pattern in which species range from rapid development and early reproduction to slow development and delayed reproduction. It summarizes recurring differences in life histories across species.
Antagonistic pleiotropy: The evolutionary process in which a genetic variant has beneficial effects on some traits but harmful effects on others. It explains age-related trade-offs through genetic effects, not only resource allocation.
Senescence: The progressive decline in survival and reproductive performance with age. Age-related decline changes the future returns from investing in maintenance.
Demography: The study of populations' size, structure, and change through births, deaths, and movement. Age-specific birth and death rates connect individual traits to population growth.

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