Origins and core questions
Life history theory asks why some organisms reproduce early and prolifically and die young while others reproduce late and sparingly and live long. David Lack (1947) proposed Lack's principle, that clutch size in birds is not simply as large as possible but matches the largest number parents can successfully raise. Lamont Cole (1954) posed Cole's paradox: an organism that breeds once and dies could match the population growth rate of one that breeds repeatedly simply by producing one extra offspring per year, leaving open why repeated breeding is so common. The answer was later found in differences between adult and juvenile survival. George Williams (1966) introduced the cost of reproduction, the idea that current reproduction reduces future survival and reproduction, refining Lack's principle.
Trade-offs and r/K selection
The central concept is the trade-off. Because energy is limited, investing in growth reduces reproduction, reproducing now lowers the chance of survival, and producing many offspring reduces the size or care each receives. MacArthur and Wilson (1967) distinguished r-selection, in low-density environments favoring rapid increase, from K-selection, near carrying capacity where competitive ability matters, and Pianka (1970) associated these with suites of traits: early maturity and many offspring versus late maturity and few. Stearns (1976, 1992) and Roff (1992), however, argued that the r/K framework was too simple and rebuilt the theory on demographic models based on age-specific mortality. Reznick et al. (2002) concluded that r/K selection has been superseded by frameworks that consider age-specific mortality together with density dependence.
Evidence and extensions
In a field experiment in Trinidadian streams, Reznick, Bryga and Endler (1990) moved guppies from high-predation sites to low-predation sites and found that within eleven years they evolved later maturity and fewer, larger offspring, consistent with the prediction that high adult mortality favors early reproduction. In a comparative analysis of mammals, Promislow and Harvey (1990) showed that a fast–slow continuum of living fast and dying young persists even after controlling for body size, and Charnov (1993) analyzed life history invariants that remain constant across species. Kirkwood's (1977) disposable soma theory explains ageing as the result of a trade-off favoring reproduction over bodily maintenance. Together with natural selection, parental investment theory and optimal foraging theory, life history theory forms a foundation of evolutionary ecology and is applied in fisheries management and conservation biology.
FAQ
- What is life history theory in simple terms?
- It explains how organisms have evolved to divide limited energy among growing, surviving and producing offspring.
- What are r-selection and K-selection?
- r-selection describes environments favoring early maturity and many offspring, and K-selection environments favoring late maturity and greater investment in fewer offspring; today they have been refined by more detailed models based on age-specific mortality.
Sources reviewed: 2026-10-26
References
- Cole, L. C. (1954). The population consequences of life history phenomena. Quarterly Review of Biology, 29(2), 103–137.
- Lack, D. (1947). The significance of clutch-size. Ibis, 89(2), 302–352.
- Williams, G. C. (1966). Natural selection, the costs of reproduction, and a refinement of Lack's principle. American Naturalist, 100(916), 687–690.
- MacArthur, R. H., & Wilson, E. O. (1967). The Theory of Island Biogeography. Princeton: Princeton University Press.
- Pianka, E. R. (1970). On r- and K-selection. American Naturalist, 104(940), 592–597.
- Stearns, S. C. (1976). Life-history tactics: A review of the ideas. Quarterly Review of Biology, 51(1), 3–47.
- Stearns, S. C. (1992). The Evolution of Life Histories. Oxford: Oxford University Press.
- Roff, D. A. (1992). The Evolution of Life Histories: Theory and Analysis. New York: Chapman & Hall.
- Reznick, D. N., Bryga, H., & Endler, J. A. (1990). Experimentally induced life-history evolution in a natural population. Nature, 346(6282), 357–359.
- Charnov, E. L. (1993). Life History Invariants. Oxford: Oxford University Press.
- Promislow, D. E. L., & Harvey, P. H. (1990). Living fast and dying young: A comparative analysis of life-history variation among mammals. Journal of Zoology, 220(3), 417–437.
- Reznick, D., Bryant, M. J., & Bashey, F. (2002). r- and K-selection revisited: The role of population regulation in life-history evolution. Ecology, 83(6), 1509–1520.
- Kirkwood, T. B. L. (1977). Evolution of ageing. Nature, 270(5635), 301–304.