Lack's principle, proposed by the British ornithologist

David Lack David Lambert Lack FRS (16 July 1910 – 12 March 1973) was a British evolutionary biologist who made contributions to ornithology, ecology, and ethology. His 1947 book, ''Darwin's Finches'', on the finches of the Galapagos Islands was a landm ...

in 1954, states that "the clutch size of each species of bird has been adapted by

natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...

to correspond with the largest number of young for which the parents can, on average, provide enough food". As a biological rule, the principle can be formalised and generalised to apply to reproducing organisms in general, including animals and plants. Work based on Lack's principle by George C. Williams and others has led to an improved mathematical understanding of

population biology The term population biology has been used with different meanings. In 1971 Edward O. Wilson ''et al''. used the term in the sense of applying mathematical models to population genetics, community ecology, and population dynamics. Alan Hastings ...

Principle

Lack's principle implies that birds that happen to lay more eggs than the optimum will most likely have fewer fledglings (young that successfully fly from the nest) because the parent birds will be unable to collect enough food for them all.

Evolutionary biologist Evolutionary biology is the subfield of biology that studies the evolutionary processes (natural selection, common descent, speciation) that produced the diversity of life on Earth. It is also defined as the study of the history of life for ...

George C. Williams notes that the argument applies also to organisms other than birds, both animals and plants, giving the example of the production of

ovule In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the '' integument'', forming its outer layer, the ''nucellus'' (or remnant of the megasporangium), and the ...

s by

seed plant A spermatophyte (; ), also known as phanerogam (taxon Phanerogamae) or phaenogam (taxon Phaenogamae), is any plant that produces seeds, hence the alternative name seed plant. Spermatophytes are a subset of the embryophytes or land plants. They inc ...

s as an equivalent case. Williams formalised the argument to create a mathematical theory of evolutionary decision-making, based on the framework outlined in 1930 by

R. A. Fisher Sir Ronald Aylmer Fisher (17 February 1890 – 29 July 1962) was a British polymath who was active as a mathematician, statistician, biologist, geneticist, and academic. For his work in statistics, he has been described as "a genius who ...

, namely that the effort spent on reproduction must be worth the cost, compared to the long-term

reproductive fitness Fitness (often denoted w or ω in population genetics models) is the quantitative representation of individual reproductive success. It is also equal to the average contribution to the gene pool of the next generation, made by the same individ ...

of the individual. Williams noted that this would contribute to the discussion on whether (as Lack argued) an organism's reproductive processes are tuned to serve its own reproductive interest (

), or as V.C. Wynne-Edwards proposed, to increase the chances of survival of the

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

to which the individual belonged (

group selection Group selection is a proposed mechanism of evolution in which natural selection acts at the level of the group, instead of at the level of the individual or gene. Early authors such as V. C. Wynne-Edwards and Konrad Lorenz argued that the behavi ...

). The zoologist J.L. Cloudsley-Thompson argued that a large bird would be able to produce more young than a small bird. Williams replied that this would be a bad reproductive strategy, as large birds have lower mortality and therefore a higher residual reproductive value over their whole lives (so taking a large short-term risk is unjustified). Williams' reply "is one of the most cited papers in life history evolution because it ... made it conceptually possible to find the optimal life history strategies in age-structured populations".

References

{{Biological rules Biological rules Evolution of birds Evolutionary biology

Principle

See also

References