Kin recognition

Kin recognition (kin detection) refers to an organism's potential ability to distinguish between close genetic kin and non-kin. In evolutionary biology and in psychology, such capabilities are presumed to have evolved to serve the adaptive function of inbreeding avoidance.

An additional adaptive function sometimes posited for kin recognition is its possible role in relation to kin selection. There is debate over this additional role, since in strict theoretical terms that it is not necessary for kin altruism or the cooperation that accompanies it. Additionally, in experimental results, active powers of recognition play a negligible role in mediating social cooperation relative to less elaborate cue-based mechanisms, such as familiarity, imprinting and phenotype matching. Nevertheless, much research has been produced investigating the possible role of kin recognition mechanisms in mediating altruism.

Because kin recognition is overwhelmingly cue-based, outcomes are non-deterministic in relation to actual genetic kinship. A well-known example is the Westermarck effect, in which unrelated individuals who 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 (see Social Bonding and Nurture Kinship).

Theoretical background

Hamilton's theory of inclusive fitness and the related theory of kin selection were formalized in the 1960s and 1970s in an attempt to explain the conditions surrounding the evolution of social behaviours. Hamilton's early papers, as well as giving a mathematical account of the selection pressure, also included wide ranging discussion about possible implications and behavioural manifestations. In one area, Hamilton discusses potential roles of cue-based mechanisms mediating altruism versus the possibility of '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)

This possibility served as the main impetus for a generation of researchers to start looking for evidence of any 'positive powers' of kin discrimination. Later however, Hamilton had developed his thinking to consider that such discriminatory behaviour was unlikely to play a role in mediating social 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)

The implication that inclusive fitness theory 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)

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).

Criticism

Leading inclusive fitness theorists such as 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)

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)

However, recent evidence suggests that kin recognition can also be mediated by immunogenetic similarity of the major histocompatibility complex (MHC). For a discussion of the interaction of these social and biological kin recognition factors see Lieberman, Tooby, and Cosmides (2007). Some have suggested that, as applied to humans, this nature-nurture interactionist perspective allows a synthesis between theories and evidence of social bonding and cooperation across the fields of evolutionary biology, psychology (attachment theory) and cultural anthropology (nurture kinship).

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 are 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.”

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 ground squirrel kin produce similar odors in comparison to non-kin. 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. 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. Studies suggest that the Bald- faced hornet, Dolichovespula maculata, can recognize nest mates by their cuticular hydrocarbon profile, which produces a distinct smell.

Inbreeding avoidance

As noted above, kin recognition is presumed to have evolved to serve the adaptive function of inbreeding avoidance. Below, some examples are presented that illustrate the basis for this presumption.

When mice inbreed with close relatives in their natural habitat, there is a significant detrimental effect on progeny survival. Since inbreeding is detrimental, it tends to be avoided. 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. 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.

In toads, male advertisement vocalizations may serve as cues by which females recognize their kin and thus avoid inbreeding.

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. Thus kin recognition at the level of the pollen tube apparently leads to post-pollination selection in order to avoid inbreeding depression. Also, seeds may be aborted selectively depending on donor–recipient relatedness.

See also

• Inclusive fitness
• Kin selection
• Nurture kinship
• Attachment theory