W. D. Hamilton
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| - | In [[evolutionary biology]], '''parental investment''' (PI) is any parental expenditure (time, energy etc.) that benefits one [[offspring]] at a cost to [[parent]]s' ability to invest in other components of [[fitness (biology)|fitness]] (Clutton-Brock 1991: 9; Trivers 1972). Components of fitness (Beatty 1992) include the wellbeing of existing offspring, parents' future [[sexual reproduction|reproduction]], and [[inclusive fitness]] through aid to kin ([[W. D. Hamilton|Hamilton]], 1964). Parental investment is sometimes incorrectly equated with parental care or parental effort. | + | '''William Donald Hamilton''' [[Royal Society|FRS]] (1 August 1936 – 7 March 2000) was a [[United Kingdom|British]] [[evolutionary biologist]], widely recognised as one of the greatest [[evolution]]ary theorists of the 20th century. |
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| - | Parental investment theory is a branch of [[life history theory]]. The earliest consideration of parental investment is given by Fisher (1930), [[Fisher's principle]], he argued parental expenditure on both sexes should be equal. Clutton-Brock (1991: 9) expanded the concept of PI to include costs to any other component of parental fitness. | + | |
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| - | [[Robert Trivers]]' theory of parental investment predicts that the [[sex]] making the largest investment in [[lactation]], nurturing and protecting offspring will be more discriminating in [[mating]] and that the sex that invests less in offspring will compete for access to the higher investing sex (see [[Bateman's principle]]. Sex differences in parental effort are important in determining the strength of [[sexual selection]]. | + | |
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| - | Reproduction is costly. Individuals are limited in the degree to which they can devote time and resources to producing and raising their young, and such expenditure may also be detrimental to their future condition, survival and further reproductive output. | + | |
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| - | However, such expenditure is typically beneficial to the offspring, enhancing their condition, survival and reproductive success. These differences may lead to [[parent–offspring conflict|parent-offspring conflict]]. Parental investment can be provided by the [[female]] (female uniparental care), the [[male]] (male uniparental care), or both (biparental care). Parents are naturally selected to maximise the difference between the benefits and the costs, and parental care will tend to exist when the benefits are substantially greater than the costs. | + | |
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| - | Parental care is found in a broad range of taxonomic groups including both [[ectotherm]]ic (invertebrates, fish, amphibians and reptiles) and [[warm-blooded|endothermic]] (birds and mammals) species. Care can be provided at any stage of the offspring life: pre-natal care including behaviours such as egg guarding, preparation of nest, brood carrying, incubation and placental nourishment in mammals and post-natal care including food provisioning, protection of offspring. | + | |
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| - | In [[Semelparity and iteroparity|iteroparous]] species, where individuals may go through several reproductive bouts during their lifetime, a trade-off may exist between investment in current offspring and future reproduction. Parents need to balance their offspring demands against their own self-maintenance. This potential negative effect of parental care was explicitly formalised by Trivers (1972) who originally defined the term ''parental investment'' to mean ''any investment by the parent in an individual offspring that increases the offspring's chance of surviving (and hence [[reproductive success]]) at the cost of the parent's ability to invest in other offspring''. | + | |
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| - | The benefits of parental investment to the offspring are large and are associated with the effects on condition, growth, survival and ultimately, on reproductive success of the offspring. However, these benefits can come at the cost of parent's ability to reproduce in the future e.g. through the increased risk of injury when defending offspring against predators, the loss of mating opportunities whilst rearing offspring and an increase in the time to the next reproduction. | + | |
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| - | Overall, parents are [[selection|selected]] to maximise the difference between the benefits and the costs, and parental care will be likely to evolve when the benefits exceed the costs. | + | |
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| - | == See also == | + | |
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| - | * [[Kin selection]] | + | |
| - | * [[Cinderella effect]] | + | |
| - | * [[r/K selection theory]] | + | |
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Revision as of 20:58, 12 December 2010
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William Donald Hamilton FRS (1 August 1936 – 7 March 2000) was a British evolutionary biologist, widely recognised as one of the greatest evolutionary theorists of the 20th century.
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