Lack's principle, proposed by the British

ornithologist Ornithology, from Ancient Greek ὄρνις (''órnis''), meaning "bird", and -logy from λόγος (''lógos''), meaning "study", is a branch of zoology dedicated to the study of birds. Several aspects of ornithology differ from related discip ...

David Lack 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 Heredity, heritable traits characteristic of a population over generation ...

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 Hasting ...

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 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 sporangium, megasporangium), ...

s by

seed plant A seed plant or spermatophyte (; New Latin ''spermat-'' and Greek ' (phytón), plant), also known as a phanerogam (taxon Phanerogamae) or a phaenogam (taxon Phaenogamae), is any plant that produces seeds. It is a category of embryophyte (i.e. la ...

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, 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 a 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 individuals ...

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 A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

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 beha ...

). 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