Ability of an organism to distinguish between close genetic kin and non-kin
Kin recognition, also called kin detection, is an organism's ability to distinguish between close genetic kin and non-kin. In evolutionary biology and psychology, such an ability is presumed to have evolved for inbreeding avoidance,[1] though animals do not typically avoid inbreeding.[2]
An additional adaptive function sometimes posited for kin recognition is a role in kin selection. There is debate over this, since in strict theoretical terms kin recognition is not necessary for kin selection or the cooperation associated with it. Rather, social behaviour can emerge by kin selection in the demographic conditions of 'viscous populations' with organisms interacting in their natal context, without active kin discrimination, since social participants by default typically share recent common origin. Since kin selection theory emerged, much research has been produced investigating the possible role of kin recognition mechanisms in mediating altruism. Taken as a whole, this research suggests that active powers of recognition play a negligible role in mediating social cooperation relative to less elaborate cue-based and context-based mechanisms, such as familiarity, imprinting and phenotype matching.
Because cue-based 'recognition' predominates in social mammals, outcomes are non-deterministic in relation to actual genetic kinship, instead outcomes simply reliably correlate with genetic kinship in an organism's typical conditions. A well-known human example of an inbreeding avoidance mechanism is the Westermarck effect, in which unrelated individuals who happen to spend their childhood in the same household find each other sexually unattractive. Similarly, due to the cue-based mechanisms that mediate social bonding and cooperation, unrelated individuals who grow up together in this way are also likely to demonstrate strong social and emotional ties, and enduring altruism.
Theoretical background
The English evolutionary biologist W. D. Hamilton's theory of inclusive fitness, and the related theory of kin selection, were formalized in the 1960s and 1970s to explain the evolution of social behaviours. Hamilton's early papers, as well as giving a mathematical account of the selection pressure, discussed possible implications and behavioural manifestations. Hamilton considered potential roles of cue-based mechanisms mediating altruism versus 'positive powers' of kin discrimination:
The selective advantage which makes behaviour conditional in the right sense on the discrimination of factors which correlate with the relationship of the individual concerned is therefore obvious. It may be, for instance, that in respect of a certain social action performed towards neighbours indiscriminately, an individual is only just breaking even in terms of inclusive fitness. If he could learn to recognise those of his neighbours who really were close relatives and could devote his beneficial actions to them alone an advantage to inclusive fitness would at once appear. Thus, a mutation causing such discriminatory behaviour itself benefits inclusive fitness and would be selected. In fact, the individual may not need to perform any discrimination so sophisticated as we suggest here; a difference in the generosity of his behaviour according to whether the situations evoking it were encountered near to, or far from, his own home might occasion an advantage of a similar kind." (1996 [1964], 51)[3]
These two possibilities, altruism mediated via 'passive situation' or via 'sophisticated discrimination', stimulated a generation of researchers to look for evidence of any 'sophisticated' kin discrimination. However, Hamilton later (1987) developed his thinking to consider that "an innate kin recognition adaptation" was unlikely to play a role in mediating altruistic behaviours:
But once again, we do not expect anything describable as an innate kin recognition adaptation, used for social behaviour other than mating, for the reasons already given in the hypothetical case of the trees.(Hamilton 1987, 425)[4]
The implication that the inclusive fitness criterion can be met by mediating mechanisms of cooperative behaviour that are context and location-based has been clarified by recent work by West et al.:
In his original papers on inclusive fitness theory, Hamilton pointed out a sufficiently high relatedness to favour altruistic behaviours could accrue in two ways—kin discrimination or limited dispersal (Hamilton, 1964, 1971, 1972, 1975). There is a huge theoretical literature on the possible role of limited dispersal reviewed by Platt & Bever (2009) and West et al. (2002a), as well as experimental evolution tests of these models (Diggle et al., 2007; Griffin et al., 2004; Kümmerli et al., 2009 ). However, despite this, it is still sometimes claimed that kin selection requires kin discrimination (Oates & Wilson, 2001; Silk, 2002 ). Furthermore, a large number of authors appear to have implicitly or explicitly assumed that kin discrimination is the only mechanism by which altruistic behaviours can be directed towards relatives... [T]here is a huge industry of papers reinventing limited dispersal as an explanation for cooperation. The mistakes in these areas seem to stem from the incorrect assumption that kin selection or indirect fitness benefits require kin discrimination (misconception 5), despite the fact that Hamilton pointed out the potential role of limited dispersal in his earliest papers on inclusive fitness theory (Hamilton, 1964; Hamilton, 1971; Hamilton, 1972; Hamilton, 1975). (West et al. 2010, p. 243 and supplement)[5]
For a recent review of the debates around kin recognition and their role in the wider debates about how to interpret inclusive fitness theory, including its compatibility with ethnographic data on human kinship, see Holland (2012).[6]
Criticism
Leading inclusive fitness theorists such as Alan Grafen have argued that the whole research program around kin recognition is somewhat misguided:
Do animals really recognise kin in a way that is different from the way they recognise mates, neighbours, and other organisms and objects?. Certainly animals use recognition systems to recognise their offspring, their siblings and their parents. But to the extent that they do so in the same way that they recognise their mates and their neighbours, I feel it is unhelpful to say they have a kin recognition system." (Grafen 1991, 1095)[7]
Others have cast similar doubts over the enterprise:
[T]he fact that animals benefit from engaging in spatially mediated behaviors is not evidence that these animals can recognize their kin, nor does it support the conclusion that spatially based differential behaviors represent a kin recognition mechanism (see also discussions by Blaustein, 1983; Waldman, 1987; Halpin 1991). In other words, from an evolutionary perspective it may well be advantageous for kin to aggregate and for individuals to behave preferentially towards nearby kin, whether or not this behaviour is the result of kin recognition per se" (Tang-Martinez 2001, 25)[8]
Experimental evidence
Kin recognition is a behavioral adaptation noted in many species but proximate level mechanisms are not well documented. Recent studies have shown that kin recognition can result from a multitude of sensory input. Jill Mateo notes that there are three components prominent in kin recognition. First, "production of unique phenotypic cues or labels". Second, "perception of these labels and the degree of correspondence of these labels with a 'recognition template'", and finally the recognition of the phenotypes should lead to "action taken by the animal as a function of the perceived similarity between its template and an encountered phenotype".[9]
The three components allow for several possible mechanisms of kin recognition. Sensory information gathered from visual, olfactory and auditory stimuli are the most prevalent. The Belding's ground squirrel kin produce similar odors in comparison to non-kin.[10] Mateo notes that the squirrels spent longer investigating non-kin scents suggesting recognition of kin odor. It's also noted that Belding's ground squirrels produce at least two scents arising from dorsal and oral secretions, giving two opportunities for kin recognition. In addition, the Black Rock Skink is also able to use olfactory stimuli as a mechanism of kin recognition. Egernia saxatilis have been found to discriminate kin from non-kin based on scent. Egernia striolata also use some form of scent, most likely through skin secretions.[11] However, Black Rock Skinks discriminate based on familiarity rather than genotypic similarity. Juvenile E. saxatilis can recognize the difference between the scent of adults from their own family group and unrelated adults. Black Rock Skink recognize their family groups based on prior association and not how genetically related the other lizards are to themselves.[12] Auditory distinctions have been noted among avian species. Long-tailed tits (Aegithalos caudatus) are capable of discriminating kin and non-kin based on contact calls. Distinguishing calls are often learned from adults during the nestling period.[13] Studies suggest that the bald-faced hornet, Dolichovespula maculata, can recognize nest mates by their cuticular hydrocarbon profile, which produces a distinct smell.[14]
Kin recognition in some species may also be mediated by immunogenetic similarity of the major histocompatibility complex (MHC).[15] For a discussion of the interaction of these social and biological kin recognition factors see Lieberman, Tooby, and Cosmides (2007).[16] Some have suggested that, as applied to humans, this nature-nurture interactionist perspective allows a synthesis[6] between theories and evidence of social bonding and cooperation across the fields of evolutionary biology, psychology (attachment theory) and cultural anthropology (nurture kinship).
In Plants
Kin recognition is an adaptive behavior observed in living beings to prevent inbreeding, and increase fitness of populations, individuals and genes. Kin recognition is the key to successful reciprocal altruism, a behavior that increases reproductive success of both organisms involved. Reciprocal altruism as a product of kin recognition has been observed and studied in many animals, and more recently, plants. Due to the nature of plant reproduction and growth, plants are more likely than animals to live in close proximity to family members, and therefore stand to gain more from the ability to differentiate kin from strangers.[17]
In recent years, botanists have been conducting studies to determine which plant species can recognize kin, and discover the responses of plants to neighboring kin. Murphy and Dudley (2009) shows that Impatiens pallida has the ability to recognize individuals closely related to them and those not related to them. The physiological response to this recognition is increasingly interesting. I. pallida responds to kin by increasing branchiness and stem elongation, to prevent shading relatives, and responds to strangers by increasing leaf to root allocation, as a form of competition.[18]
Root allocation has been a very common trait shown through research in plants. Limited amounts of biomass can cause trade-offs among the construction of leaves, stems, and roots overall. But, in plants that recognize kin, the movement of resources in the plant has been shown to be affected by proximity to related individuals.[19] It is well documented that roots can emit volatile compounds in the soil and that interactions also occur below-ground between plant roots and soil organisms. This has mainly focused on organisms in the kingdom Animalia, however.
Regarding this, root systems are known to exchange carbon and defense related molecular signals via connected mycorrhizal networks. For instance, it has been demonstrated that tobacco plants can detect the volatile chemical ethylene in order to form a “shade-avoidance phenotype.”[20] Barley plants were also shown to allocate biomass to their roots when exposed to chemical signals from members of the same species,[20] showing that, if they can recognize those signals for competition, recognition of kin in the plant could be likely via a similar chemical response.
Similarly, Bhatt et al. (2010) show that Cakile edentula, the American sea rocket, has the ability to allocate more energy to root growth, and competition, in response to growing next to a stranger, and allocates less energy to root growth when planted next to a sibling. This reduces competition between siblings and increases fitness of relatives growing next to each other, while still allowing competition between non-relative plants.[21]
Little is known about the mechanisms involved in kin recognition. They most likely vary between species as well as within species. A study by Bierdrzycki et al. (2010) shows that root secretions are necessary for Arabidopsis thaliana to recognize kin vs. strangers, but not necessary to recognize self vs. non-self roots. This study was performed using secretion inhibitors, which disabled the mechanism responsible for kin recognition in this species, and showed similar growth patterns to Bhatt et al., (2010) and Murphy and Dudley (2009) in control groups. The most interesting result of this study was that inhibiting root secretions did not reduce the ability of Arabidopsis to recognize their own roots, which implicates a separate mechanism for self/non-self recognition than that for kin/stranger recognition.[22]
While this mechanism in the roots responds to exudates and involves competition over resources like nitrogen and phosphorus, another mechanism has been recently proposed, which involves competition over light, in which kin recognition takes place in leaves. In their 2014 study, Crepy and Casal conducted multiple experiments on different accessions of A. thaliana. These experiments showed that Arabidopsis accessions have distinct R:FR and blue light signatures, and that these signatures can be detected by photoreceptors, which allows the plant to recognize its neighbor as a relative or non-relative. Not much is known about the pathway that Arabidopsis uses to associate these light patterns with kin, however, researchers ascertained that photoreceptors phyB, cry 1, cry 2, phot1, and phot2 are involved in the process by performing a series of experiments with knock-out mutants. Researchers also concluded that the auxin-synthesis gene TAA1 is involved in the process, downstream of the photoreceptors, by performing a similar experiments using Sav3 knock-out mutants. This mechanism leads to altered leaf direction to prevent shading of related neighbors and to reduce competition for sunlight.[23]
When mice inbreed with close relatives in their natural habitat, there is a significant detrimental effect on progeny survival.[24] Since inbreeding can be detrimental, it tends to be avoided by many species. In the house mouse, the major urinary protein (MUP) gene cluster provides a highly polymorphic scent signal of genetic identity that appears to underlie kin recognition and inbreeding avoidance. Thus there are fewer matings between mice sharing MUP haplotypes than would be expected if there were random mating.[25] Another mechanism for avoiding inbreeding is evident when a female house mouse mates with multiple males. In such a case, there appears to be egg-driven sperm selection against sperm from related males.[26]
In toads, male advertisement vocalizations may serve as cues by which females recognize their kin and thus avoid inbreeding.[27]
In dioecious plants, the stigma may receive pollen from several different potential donors. As multiple pollen tubes from the different donors grow through the stigma to reach the ovary, the receiving maternal plant may carry out pollen selection favoring pollen from less related donor plants.[28] Thus, kin recognition at the level of the pollen tube apparently leads to post-pollination selection to avoid inbreeding depression. Also, seeds may be aborted selectively depending on donor–recipient relatedness.[28]
Altruism is the principle and practice of concern for the well-being and/or happiness of other humans or animals. While objects of altruistic concern vary, it is an important moral value in many cultures and religions. It may be considered a synonym of selflessness, the opposite of selfishness.
In evolutionary biology, reciprocal altruism is a behaviour whereby an organism acts in a manner that temporarily reduces its fitness while increasing another organism's fitness, with the expectation that the other organism will act in a similar manner at a later time.
The Selfish Gene is a 1976 book on evolution by the ethologist Richard Dawkins, in which the author builds upon the principal theory of George C. Williams's Adaptation and Natural Selection (1966). Dawkins uses the term "selfish gene" as a way of expressing the gene-centred view of evolution, popularising ideas developed during the 1960s by W. D. Hamilton and others. From the gene-centred view, it follows that the more two individuals are genetically related, the more sense it makes for them to behave cooperatively with each other.
Kin selection is a process whereby natural selection favours a trait due to its positive effects on the reproductive success of an organism's relatives, even when at a cost to the organism's own survival and reproduction. Kin selection can lead to the evolution of altruistic behaviour. Kin selection is related to the concept of inclusive fitness, which combines the number of offspring produced with the number an individual can ensure the production of by supporting others. A broader definition of kin selection includes selection acting on interactions between individuals who share a gene of interest even if the gene is not shared due to common ancestry.
Behavioral ecology, also spelled behavioural ecology, is the study of the evolutionary basis for animal behavior due to ecological pressures. Behavioral ecology emerged from ethology after Niko Tinbergen outlined four questions to address when studying animal behaviors: What are the proximate causes, ontogeny, survival value, and phylogeny of a behavior?
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.
In evolutionary biology, inclusive fitness is one of two metrics of evolutionary success as defined by W. D. Hamilton in 1964:
Evolutionary game theory (EGT) is the application of game theory to evolving populations in biology. It defines a framework of contests, strategies, and analytics into which Darwinian competition can be modelled. It originated in 1973 with John Maynard Smith and George R. Price's formalisation of contests, analysed as strategies, and the mathematical criteria that can be used to predict the results of competing strategies.
Fictive kinship is a term used by anthropologists and ethnographers to describe forms of kinship or social ties that are based on neither consanguineal nor affinal ties. It contrasts with true kinship ties.
Social grooming is a behavior in which social animals, including humans, clean or maintain one another's body or appearance. A related term, allogrooming, indicates social grooming between members of the same species. Grooming is a major social activity, and a means by which animals who live in close proximity may bond and reinforce social structures, family links, and build companionships. Social grooming is also used as a means of conflict resolution, maternal behavior and reconciliation in some species. Mutual grooming typically describes the act of grooming between two individuals, often as a part of social grooming, pair bonding, or a precoital activity.
In biology, altruism refers to behaviour by an individual that increases the fitness of another individual while decreasing the fitness of themselves. Altruism in this sense is different from the philosophical concept of altruism, in which an action would only be called "altruistic" if it was done with the conscious intention of helping another. In the behavioural sense, there is no such requirement. As such, it is not evaluated in moral terms—it is the consequences of an action for reproductive fitness that determine whether the action is considered altruistic, not the intentions, if any, with which the action is performed.
In evolution, cooperation is the process where groups of organisms work or act together for common or mutual benefits. It is commonly defined as any adaptation that has evolved, at least in part, to increase the reproductive success of the actor's social partners. For example, territorial choruses by male lions discourage intruders and are likely to benefit all contributors.
Eusociality evolved repeatedly in different orders of animals, particularly the Hymenoptera. This 'true sociality' in animals, in which sterile individuals work to further the reproductive success of others, is found in termites, ambrosia beetles, gall-dwelling aphids, thrips, marine sponge-dwelling shrimp, naked mole-rats, and the insect order Hymenoptera. The fact that eusociality has evolved so often in the Hymenoptera, but remains rare throughout the rest of the animal kingdom, has made its evolution a topic of debate among evolutionary biologists. Eusocial organisms at first appear to behave in stark contrast with simple interpretations of Darwinian evolution: passing on one's genes to the next generation, or fitness, is a central idea in evolutionary biology.
Darwinian anthropology describes an approach to anthropological analysis which employs various theories from Darwinian evolutionary biology. Whilst there are a number of areas of research that can come under this broad description some specific research projects have been closely associated with the label. A prominent example is the project that developed in the mid 1970s with the goal of applying sociobiological perspectives to explain patterns of human social relationships, particularly kinship patterns across human cultures.
Social Bonding and Nurture Kinship: Compatibility between Cultural and Biological Approaches is a book on human kinship and social behavior by Maximilian Holland, published in 2012. The work synthesizes the perspectives of evolutionary biology, psychology and sociocultural anthropology towards understanding human social bonding and cooperative behavior. It presents a theoretical treatment that many consider to have resolved longstanding questions about the proper place of genetic connections in human kinship and social relations, and a synthesis that "should inspire more nuanced ventures in applying Darwinian approaches to sociocultural anthropology". The book has been called "A landmark in the field of evolutionary biology" which "gets to the heart of the matter concerning the contentious relationship between kinship categories, genetic relatedness and the prediction of behavior", "places genetic determinism in the correct perspective" and serves as "a shining example of what can be achieved when excellent scholars engage fully across disciplinary boundaries."
Inbreeding avoidance, or the inbreeding avoidance hypothesis, is a concept in evolutionary biology that refers to the prevention of the deleterious effects of inbreeding. Animals only rarely exhibit inbreeding avoidance. The inbreeding avoidance hypothesis posits that certain mechanisms develop within a species, or within a given population of a species, as a result of assortative mating and natural and sexual selection, in order to prevent breeding among related individuals. Although inbreeding may impose certain evolutionary costs, inbreeding avoidance, which limits the number of potential mates for a given individual, can inflict opportunity costs. Therefore, a balance exists between inbreeding and inbreeding avoidance. This balance determines whether inbreeding mechanisms develop and the specific nature of such mechanisms.
Inclusive fitness in humans is the application of inclusive fitness theory to human social behaviour, relationships and cooperation.
The tree-crevice skink or tree skink (Egernia striolata) is a species of skink, a lizard in the family Scincidae. The species is endemic to Australia and is found in the states of Victoria, the Northern Territory, Queensland, New South Wales and South Australia. E. striolata tend to live in crevices and cracks in hollow logs or rocks. They greatly prefer heterogeneous and structurally diverse habitats and their behavior changes depending on the habitat they live in.
Liselotte Sundström is a Finnish zoologist. She is professor emerita of evolutionary biology at the University of Helsinki.
The cognitive ecology of individual recognition has been studied in many species, especially in primates or other mammalian species that exhibit complex social behaviours, but comparatively little research has been done on colonial birds. Colonial birds live in dense colonies in which many individuals interact with each other daily. For colonial birds, being able to identify and recognize individuals can be a crucial skill.
References
↑ Tanskanen, Antti O.; Danielsbacka, Mirkka (2021), "Kin Recognition", in Shackelford, Todd K.; Weekes-Shackelford, Viviana A. (eds.), Encyclopedia of Evolutionary Psychological Science, Cham: Springer International Publishing, pp.4371–4373, doi:10.1007/978-3-319-19650-3_1359, ISBN978-3-319-19650-3, retrieved 2022-07-31
↑ Sherman, P. W. (1981). "Kinship, Demography, and Belding's Ground Squirrel Nepotism." Behavioral Ecology and Sociobiology 8: 251-259.
↑ Bull, C. Michael; Griffin, Clare L.; Bonnett, Matthew; Gardner, Michael G.; Cooper, Steven J. B. (2001). "Discrimination between Related and Unrelated Individuals in the Australian Lizard Egernia striolata". Behavioral Ecology and Sociobiology. 50 (2): 173–179. ISSN 0340-5443.
↑ David E. O'Connor, Richard Shine, Kin discrimination in the social lizard Egernia saxatilis (Scincidae), Behavioral Ecology, Volume 17, Issue 2, March/April 2006, Pages 206–211, doi:10.1093/beheco/arj019
↑ Discrimination Between Natal and Non- Natal Nests by the Social Wasps Dolichovespula maculata and Polistes fuscatus. Journal of the Kansas Entomological Society. Deanna Ferguson, George J. Gamboa and Julia K. Jones. Departement of Biological Sciences, Oakland University.
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