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inclusive fitness
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What does fitness mean in biology?
In biology, fitness, also known as Darwinian fitness, is the capability of an organism to survive and pass on its genotype to offspring via reproduction, especially when compared to other organisms.
Inclusive fitness theory states that an organism's genetic success is based on cooperation and altruistic behavior. Altruism among organisms sharing genes helps pass those genes to future generations, enhancing the genetic fitness of both the altruistic organism and the recipient. Inclusive fitness applies only to relatives and is called kin selection.
British geneticist J.B.S. Haldane first proposed the idea of inclusive fitness in 1932. Later, British evolutionary biologist William Donald Hamilton named and developed the theory to explain direct (reproductive) and indirect inheritance of genetic traits associated with altruism.
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What is inclusive fitness?
Inclusive fitness theory in evolutionary biology suggests that an organism's genetic success comes from cooperation and altruistic behavior. Altruism among organisms sharing genes allows those genes to pass to future generations. An altruistic act supporting a relative enhances the genetic fitness of both the recipient and the altruistic organism. Propagating shared genes underlies the evolution of eusociality, cooperative behavior with division of labor and group integration, mainly in social insects. Inclusive fitness is commonly applied to eusocial organisms like bees and ants and also explains cooperative breeding in animals like birds.
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How does helping relatives increase an organism's inclusive fitness?
Inclusive fitness theory suggests that organisms can increase their overall genetic success through altruistic behaviors that support the survival of relatives.
Hamilton's rule explains this mathematically: (r \times B > C), where B is the benefit to the recipient, C is the cost to the altruist, and r is the genetic relatedness between them. Altruism evolves if the benefit to relatives, weighted by their relatedness, outweighs the cost to the individual.
For example, a female lion nursing her sister's cub increases her inclusive fitness because the benefit to her sister's offspring compensates for the slight reduction in her own cub's survival probability. Because relatives share genes, helping them survive and reproduce indirectly promotes the altruist's genes, including those for altruism.
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What is kin selection, and how is it related to inclusive fitness?
Kin selection considers the role relatives play when evaluating the genetic fitness of a given individual and occurs when an animal engages in self-sacrificial behavior that benefits the genetic fitness of its relatives.
Inclusive fitness is a theory in evolutionary biology where an organism’s genetic success comes from cooperation and altruistic behavior. It suggests that altruism among organisms who share a percentage of genes enables those genes to pass to future generations, enhancing the genetic fitness of both the recipient and the altruistic organism.
Kin selection is based on the concept of inclusive fitness, which is made up of individual survival and reproduction (direct fitness) and any impact that an individual has on the survival and reproduction of relatives (indirect fitness). Inclusive fitness applies only to relatives and considers genetic traits in both related and unrelated individuals.
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How do behaviors like sharing food or warning calls relate to inclusive fitness?
Inclusive fitness explains how behaviors like sharing food or giving warning calls can evolve through natural selection. It considers the impact of a trait on both the individual performing the behavior and on others who share its genes.
Altruistic acts, such as Belding's ground squirrels warning others of predators, increase the survival chances of relatives. Similarly, cooperative behaviors like food sharing among related individuals can enhance the propagation of shared genes.
Hamilton's rule (r × B > C) suggests altruism evolves when the benefit to the recipient (B), weighted by the genetic relatedness (r), exceeds the cost (C) to the altruist. This means that by helping relatives, individuals can increase the representation of their genes in future generations, even if it comes at a personal cost.
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Why is inclusive fitness important in explaining social behaviors in animals?
Inclusive fitness is important in explaining social behaviors in animals because it suggests that altruism among organisms sharing genes enables those genes to be passed on. Altruistic acts supporting a relative's survival enhances the genetic fitness of both the recipient and the altruistic organism.
Hamilton's rule recognizes that individuals pass on genes by helping relatives reproduce through altruistic behavior. Inclusive fitness theory is commonly applied to eusocial organisms, like bees and ants, but also explains cooperative breeding in birds and adoption in red squirrels.
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inclusive fitness, theory in evolutionary biology in which an organism’s genetic success is believed to be derived from cooperation and altruistic behaviour. Inclusive fitness theory suggests that altruism among organisms who share a given percentage of genes enables those genes to be passed on to subsequent generations. In this way, an altruistic act that supports the survival of a relative or other individual theoretically enhances the genetic fitness of both the recipient of the act and the altruistic organism. The propagation of shared genes was believed to be an underlying mechanism for the evolution of eusociality (cooperative behaviour characterized by division of labour and group integration that is found in certain species of animals, mainly social insects).
The idea of inclusive fitness was first proposed in 1932 by British geneticist J.B.S. Haldane in The Causes of Evolution. The theory was later named and developed by British evolutionary biologist William Donald Hamilton, who used inclusive fitness to explain direct (reproductive) and indirect (aided by a relative or a colony member) inheritance of genetic traits associated with altruism. Hamilton presented his inclusive fitness theory in 1963; the following year British evolutionary biologist John Maynard Smith coined the term kin selection to describe Hamilton’s theory. Inclusive fitness later came to be understood as forming a general basis for kin selection theory, which attempts to interpret altruistic social behaviour in animals through genetic relatedness and benefits and costs associated with altruistic acts. Thus, in contrast to inclusive fitness, which considers genetic traits in both related and unrelated individuals, kin selection is concerned only with relatives. Hamilton’s inclusive fitness theory, as well as kin selection, seemed to many biologists to reconcile the conflict between natural selection, in which “selfish” genes perpetuate their own fitness through survival of the fittest, and selfless behaviour, in which eusocial genes shared by relatives and colony members influence cooperative behaviours that encourage the propagation of those genes.
Inclusive fitness theory is most commonly applied to eusocial organisms, such as bees and ants, although it has also been invoked to explain cooperative breeding in animals such as birds and the adoption of orphaned young by asocial red squirrels (Tamiasciurus hudsonicus). In certain bird species, such as the Florida scrub jay (Aphelocoma coerulescens) and the groove-billed ani (Crotophaga sulcirostris), some individuals will stay near nesting sites and participate in the rearing of related offspring. Individuals that do not disperse to their own territories have been thought to perceive the inclusive fitness gains of cooperative breeding as being greater than fitness gains offered by dispersal to potentially less-favourable territory. In such instances, inclusive fitness through cooperative breeding is the result of constraints on territory quality and is influenced by factors such as food, mate attraction, and predation. Indeed, in the absence of constraints, staying near relatives is less advantageous, potentially limiting breeding opportunities and thereby making kin selection and inclusive fitness less beneficial to reproductive success. The amount of labour that cooperative breeding individuals contribute to raising relatives is variable. In contrast, eusocial organisms have fixed and stereotyped divisions of labour; castes such as sterile workers presumably accumulate reproductive advantages by helping their relatives in the cooperative raising of young.
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Although some researchers still contend that inclusive fitness can be used to describe the evolution of eusociality, the theory’s empirical assumptions and relevance to only very specialized social structures have led others to challenge its validity. American biologists Edward O. Wilson, Martin A. Nowak, and Corina E. Tarnita have provided mathematical explanations for eusociality based on population genetics and natural selection. By analyzing hypothetical populations of organisms in different evolutionary scenarios, the researchers determined that competition between selection for a eusocial allele (one of a pair of genes) and selection for a solitary allele was determined by basic principles guiding natural selection rather than by selection factors that extend beyond standard fitness calculations. The researchers further concluded that genetic relatedness is a consequence of cooperation and eusociality, not a driving force behind the evolution of these characteristics.