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Life-history theory

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Life history theory is a method of analysis in animal and human biology, psychology, and especially evolutionary sociobiology which postulates that many of the physiological traits and behaviors of individuals may be best understood in relation to the key maturational and reproductive characteristics that define the life course.

Examples of these characteristics include:

Allocation of resources

Variations of these characteristics reflect differing allocations of an individual's resources (i.e., time, effort, and energy expenditure) to competing life functions, especially growth, body maintenance, and reproduction. For an individual, the resources in a particular environment are finite. Time, effort, and energy used for one purpose diminishes the time effort, and energy available for another. For example, resources spent growing to a larger body size cannot be spent increasing the number of offspring.

Trade-offs

Thus allocation of resources involves trade-offs. These trade-offs and strategies can be compared between species. Two of the most well-known trade-offs involve number of offspring (few or many) and timing of reproduction (accelerated maturation and reproduction versus delayed, allowing for larger size and more complex social supports). The extremes at the species level of these fundamental dimensions of reproduction were recognized long before life history theory, and are traditionally termed r/K selection theory. An r-selection strategy is the production of a large number of offspring (of whom only a minority may survive) as early in life as possible. The K-selection strategy is to produce a smaller number of "fitter" offspring with higher survival chances.

According to life history theory the individuals of a species are able to make limited shifts in reproductive strategies in response to the prevailing environments. Depending on abundance of resources and probable individual longevity, individuals consciously or unconsciously shift their reproductive strategy in one direction or the other to take advantage of available resources or to compensate for resource shortage or uncertainty.

Application to humans

Life histories of individual human beings may be analyzed from the same perspectives, and the theory provides some explanatory and predictive power when applied to groups of people in different life situations. For example, it predicts that in a stressful environment, or one with uncertain resources, sexual development, mating, and pregnancy may be accelerated, with acceptance of higher risks and production of more children, while security and high resource availability tend to favor slower maturation, later mating, and fewer offspring.

Life history theory has provided new perspectives in understanding many aspects of human reproductive behavior, such as the relationship between poverty and fertility. A number of statistical predictions have been confirmed by social data, though not always reproducibly. The implications for social policy have been hotly debated because statistical associations are not always causal, and a preferred interpretation may be a more minor factor than another unpalatable relationship.

See also

Also, applications to the study of human behavior:

References

Life-history theory

  • Charnov, E. L. (1993). Life history invariants. Oxford, England: Oxford University Press.
  • Ellis, B.J. (2004). Timing of pubertal maturation in girls: an integrated life history approach. Psychological Bulletin. 130:920-58.
  • Roff, D. (1992). The evolution of life histories: Theory and analysis. New York:Chapman & Hall.
  • Roff D A (2002). Life History Evolution. Sinauer Associates Inc, MassachusettsISBN 0-87893-756-0
  • Stearns, S. (1992). The evolution of life histories. Oxford, England: Oxford University Press.

Further reading

  • Geary, D. C. (2002). Sexual selection and human life history. In R. Kail (Ed.), Advances in child development and behavior (Vol 30, pp. 41-101). San Diego, CA: Academic Press. Full text
  • Gurven, M., & Kaplan, H. (2006). Determinants of time allocation to production across the lifespan among the Machiguenga and Piro Indians of Peru. Human Nature 17, 1, 1-49. Full text (Click "Papers," and then click title.)
  • Hawkes, K. & Blurton Jones, N.J. (2005). Human age structures, paleodemography, and the Grandmother Hypothesis. In E. Voland, A. Chasiotis, and W. Schiefenhovel (Eds.), Grandmotherhood: The Evolutionary Significance of the Second Half of Female Life pp. 118-140. New Brunswick: Rutgers University Press (corrected from the published version). Full text
  • Helle, S., Lummaa, V. & Jokela., J. (2005). Late, but not early, reproduction correlated with longevity in historical Sami women. Proceedings of the Royal Society of London: Biological Sciences, 272, 29-37. Full text
  • Helle, S., Lummaa, V. & Jokela J. (2004). Selection for increased brood size in pre-industrial humans. Evolution, 52, 430-436. Full text
  • Kaplan, H.S., & Robson, A.J. (2002). The emergence of humans: The coevolution of intelligence and longevity with intergenerational transfers. PNAS, 99, 15, 10221-10226. Full text
  • Kaplan, H., Hill, K., Lancaster, J., & Hurtado, A.M. (2000). A Theory of Human Life History Evolution: Diet, Intelligence, and Longevity. Evolutionary Anthropology, 9, 4, 156-184. Full text
  • Sear, R., Mace, R. & McGregor, I.A. (2003). A life-history analysis of fertility rates in rural Gambia: evidence for trade-offs or phenotypic correlations? In J. Rodgers & H.P. Kohler (Eds.), The Biodemography of Human Reproduction and Fertility, Kluwer Press. Boston. pp 135-160. Full text
  • Walker, R., Gurven, M., Hill, K., Migliano, A., Chagnon, N., Djurovic, G., Hames, R., Hurtado, A.M., Kaplan, H., Oliver, W., de Souza, R., Valeggia, C., Yamauchi, T. (2006). Growth rates, developmental markers and life histories in 21 small-scale societies. American Journal of Human Biology, 18, 295-311. Full text (Click "Papers," and then click title.)
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