Kin selection in the context of "Inclusive fitness"

George Robert Price (October 16, 1922 – January 6, 1975) was an American population geneticist. Price is often noted for his formulation of the Price equation in 1967.

Originally a physical chemist and later a science journalist, he moved to London in 1967, where he worked in theoretical biology at the Galton Laboratory, making three important contributions: first, rederiving W.D. Hamilton's work on kin selection with the new Price equation that vindicated group selection; second, introducing (with John Maynard Smith) the concept of the evolutionarily stable strategy (ESS), a central concept in game theory; and third, formalizing Fisher's fundamental theorem of natural selection.

In the theory of evolution and natural selection, the Price equation (also known as Price's equation or Price's theorem) describes how a trait or allele changes in frequency over time. The equation uses a covariance between a trait and fitness, to give a mathematical description of evolution and natural selection. It provides a way to understand the effects that gene transmission and natural selection have on the frequency of alleles within each new generation of a population. The Price equation was derived by George R. Price, working in London to re-derive W.D. Hamilton's work on kin selection.

Examples of the Price equation have been constructed for various evolutionary cases. For example Collins and Gardner use the Price equation to partition the total change in toxin resistance in microbial communities into evolutionary change, ecological change and physiological change. Ellner et al. use the Price equation to disentangle "ecological impacts of evolution vs. non-heritable trait change", using examples from data on birds, fish and zooplankton. The Price equation also has applications in economics.

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 behaviour of animals could affect their survival and reproduction as groups, speaking for instance of actions for the good of the species. In the 1930s, Ronald Fisher and J. B. S. Haldane proposed the concept of kin selection, a form of biological altruism from the gene-centered view of evolution, arguing that animals should sacrifice for their relatives, and thereby implying that they should not sacrifice for non-relatives. From the mid-1960s, evolutionary biologists such as John Maynard Smith, W. D. Hamilton, George C. Williams, and Richard Dawkins argued that natural selection acts primarily at the level of the gene. They argued on the basis of mathematical models that individuals would not altruistically sacrifice fitness for the sake of a group unless it would ultimately increase the likelihood of an individual passing on their genes. A consensus emerged that group selection did not occur, including in special situations such as the haplodiploid social insects like honeybees (in the Hymenoptera), where kin selection explains the behaviour of non-reproductives equally well, since the only way for them to reproduce their genes is via kin.

The relationship between biology and sexual orientation is a subject of ongoing research. While scientists do not know the exact cause of sexual orientation, they theorize that it is caused by a complex interplay of genetic, hormonal, and environmental influences. However, evidence is weak for hypotheses that the postnatal social environment impacts sexual orientation, especially for males.

Biological theories for explaining the causes of sexual orientation are favored by scientists. These factors, which may be related to the development of a sexual orientation, include genes, the early uterine environment (such as prenatal hormones), and brain structure. While the evolutionary explanation for heterosexuality in organisms that reproduce sexually is straightforwardly understood to be a psychological adaptation resulting from greater reproductive success, evolutionary explanations for homosexuality rely upon other mechanisms of evolution such as kin selection and inclusive fitness, or antagonistic pleiotropy that favors heterozygotes causing homosexuality among homozygotes as a by-product.

A unit of selection is a biological entity within the hierarchy of biological organization (for example, an entity such as: a self-replicating molecule, a gene, a cell, an organism, a group, or a species) that is subject to natural selection. There is debate among evolutionary biologists about the extent to which evolution has been shaped by selective pressures acting at these different levels.

There is debate over the relative importance of the units themselves. For instance, is it group or individual selection that has driven the evolution of altruism? Where altruism reduces the fitness of individuals, individual-centered explanations for the evolution of altruism become complex and rely on the use of game theory, for instance; see kin selection and group selection. There also is debate over the definition of the units themselves, and the roles for selection and replication, and whether these roles may change in the course of evolution.