Kin-directed Behaviors Research Articles

Coresidence duration and cues of maternal investment regulate sibling altruism across cultures.

Genetic relatedness is a fundamental determinant of social behavior across species. Over the last few decades, researchers have been investigating the proximate psychological mechanisms that enable humans to assess their genetic relatedness to others. Much of this work has focused on identifying cues that predicted relatedness in ancestral environments and examining how they regulate kin-directed behaviors. Despite progress, many basic questions remain unanswered. Here we address three of these questions. First, we examine the replicability of the effect of two association-based cues to relatedness-maternal perinatal association (MPA) and coresidence duration-on sibling-directed altruism. MPA, the observation of a newborn being cared for by one's mother, strongly signals relatedness, but is only available to the older sibling in a sib-pair. Younger siblings, to whom the MPA cue is not available, appear to fall back on the duration of their coresidence with an older sibling. Second, we determine whether the effects of MPA and coresidence duration on sibling-directed altruism obtain across cultures. Last, we explore whether paternal perinatal association (PPA) informs sibship. Data from six studies conducted in California, Hawaii, Dominica, Belgium, and Argentina support past findings regarding the role of MPA and coresidence duration as cues to siblingship. By contrast, PPA had no effect on altruism. We report on levels of altruism toward full, half, and step siblings, and discuss the role alternate cues might play in discriminating among these types of siblings. (PsycINFO Database Record

Self-Reported Availability of Kinship Cues during Childhood is Associated with Kin-Directed Behavior to Parents in Adulthood

Reliable recognition of kin is an important factor in modulating kin-directed behaviors. For example, in selectively directing cooperative behavior to kin and diverting sexual interest away from them, kin first need to be recognized as such. Although an increasing number of studies have examined what information is employed in recognizing siblings and children, less is known about the information children employ in identifying their parents. In a web-based survey, we asked 702 Finnish undergraduate and graduate students to report the availability of a number of possible kinship cues during their childhood and youth. After factorization of the responses, we found that the reported amount of parental support, phenotypic similarity, and behavioral similarity generally predicted subjective certainty in relatedness and kin-directed behavior (i.e., cooperative behavior and inbreeding aversion) to parents in adulthood. Although the data suffer from their retrospective nature, the present study provides potentially useful information about kin-recognition of parents.

Genetic relatedness and spatial associations of dusky-footed woodrats (Neotoma fuscipes)

We studied the association between space sharing and kinship in a solitary rodent, the dusky-footed woodrat (Neotoma fuscipes). Genetic relatedness was inversely correlated with geographic distance for female woodrats but not for males, a pattern consistent with female philopatry and male dispersal. However, some female neighbors were unrelated, suggesting the possibility of female dispersal. Relatedness of female dyads was positively correlated with overlap of their home ranges and core areas, indicating that females were more likely to share space with relatives, whereas males showed no correlation between relatedness and the sharing of either home ranges or core areas. However, some females that shared space were not close relatives, and some closely related males shared space. House sharing was exhibited both by close relatives and by distantly related or unrelated woodrats, and was not correlated with relatedness. The kin structuring we describe likely resulted from a pattern of female philopatry and male dispersal, but also may have resulted from kin-directed behaviors by females.

Kinship on the Kibbutz: coresidence duration predicts altruism, personal sexual aversions and moral attitudes among communally reared peers

The natural experiments created by the Israeli Kibbutzim and Taiwanese minor marriages provide unique testing grounds for investigating the mechanisms governing sibling detection, inbreeding avoidance and kin-selected altruism. Here we present two studies conducted on the coreared peers of Israeli Kibbutzim. We examined how coresidence duration — a cue that would have indicated genetic relatedness in ancestral environments — impacts the development of kin-directed behaviors. In both studies, we found that coresidence duration predicts levels of altruism and sexual aversions directed toward peers. We also investigated the relationship between personal sexual aversions and moral attitudes relating to peer sexual behavior. The absence of norms proscribing sex between peers on the Kibbutz allows for a more tightly controlled investigation of this relationship. We found that total coresidence duration with opposite-sex peers predicts the intensity of moral wrongness associated with third-party peer sexual behavior, but not other behaviors, including sibling incest. More directly, we found that the summed sexual aversion felt toward all opposite-sex peers predicts levels of moral wrongness associated with third-party peer sex. Mediation analyses confirmed that personal sexual aversions mediate the relationship between coresidence duration and moral attitudes regarding peer sex. These results bolster Westermarck's original claims that childhood coresidence serves as a kinship cue, leading to greater sexual aversions and altruistic motivations, and that personal sexual aversions shape attitudes relating to third-party sexual behavior.

The cost of aggregation: juvenile salmon avoid sharing winter refuges with siblings

Kin selection advantages are usually accrued by individuals that associate with close relatives. But aggregation may also be costly, by increasing the risk of predation or resource competition, for example. As a result, individuals should increase their inclusive fitness by trading the costs and benefits of kin association and aggregation. Studies of kin selection to date have focused on situations where there is ample opportunity for kin-biased behavior and therefore for the formation of kin groups. Here we used juvenile Atlantic salmon to test an alternative strategy: that under conditions where the potential for kin-biased behavior is negligible, individuals should, when aggregating, avoid rather than associate with kin to avoid imposing the costs of aggregation upon close relatives. By testing salmon during winter, when juveniles shelter inactively in streambed refuges, we tested whether individuals associate with or avoid their siblings at a time when the opportunity for kin-directed behaviors is restricted. Our results provide the first evidence of kin avoidance in nonreproductive animals studied under semi-natural conditions. Copyright 2003.

Social monogamy in a territorial salamander

Social monogamy, which does not necessarily imply mating or genetic monogamy, is important in the formation of male–female pair associations. We operationally define social monogamy as occurring when two heterosexual adults, exclusive of kin-directed behaviour, direct significantly less aggression and significantly more submission towards each other, and/or spend significantly more time associating with each other relative to other adult heterosexual conspecifics. Long-term pair associations (i.e. those lasting through a lengthy breeding season) that are characteristic of social monogamy are common in some taxa but are virtually unknown in amphibians. Recent studies, however, have suggested that red-backed salamanders,Plethodon cinereus , have complex (for amphibians) social systems. Our laboratory experiments tested the hypothesis that red-backed salamanders found in pairs in the forest display behaviours consistent with social monogamy. During the summer noncourtship season, newly collected male–females pairs showed no preference to associate with their partners more than with a novel conspecific of the opposite sex. However, during the autumn courtship season, paired males and females significantly directed preferential behaviours towards their partners rather than towards a surrogate or a novel paired salamander. Focal animals showed no significant preferences when presented with their partner and a novel single salamander, but they never directed preferential behaviours towards a novel salamander (whether paired or single) or a surrogate. These results are the first to suggest that a salamander species engages in social monogamy. Furthermore, our results suggest that social monogamy may not inhibit paired males and females from displaying alternative strategies: preferring partners when extrapair associations may be disadvantageous (i.e. the extrapair animal is already paired) but not preferring partners when extrapair associations may be advantageous (i.e. the extrapair animal is single).

Reproductive cessation in female mammals.

In female mammals, fertility declines abruptly at an advanced age. The human menopause is one example, but reproductive cessation has also been documented in non-human primates, rodents, whales, dogs, rabbits, elephants and domestic livestock. The human menopause has been considered an evolutionary adaptation, assuming that elderly women avoid the increasing complications of continued childbirth to better nurture their current children and grandchildren. But an abrupt reproductive decline might be only a non-adaptive by-product of life-history patterns. Because so many individuals die from starvation, disease and predation, detrimental genetic traits can persist (or even be favoured) as long as their deleterious effects are delayed until an advanced age is reached, and, for a given pattern of mortality, there should be an age by which selection would be too weak to prevent the onset of reproductive senescence. We provide a systematic test of these alternatives using field data from two species in which grandmothers frequently engage in kin-directed behaviour. Both species show abrupt age-specific changes in reproductive performance that are characteristic of menopause. But elderly females do not suffer increased mortality costs of reproduction, nor do post-reproductive females enhance the fitness of grandchildren or older children. Instead, reproductive cessation appears to result from senescence.

Rethinking Oedipus: an evolutionary perspective of incest avoidance.

The author presents a biological hypothesis of incest avoidance. Pertinent literature from evolutionary biology, ethology, anthropology, and clinical research is reviewed. Secure early bonding to immediate kin predicts later adaptive kin-directed behaviors, including preferential altruism (kin selection) and incest avoidance. Impaired bonding predicts aberrant kin-directed behavior, including diminished altruism, neglect, and an increased incidence of incest. Failed bonding predicts the highest frequency of incest. Secure bonding to kin may function to establish adaptive kin-directed behaviors, including incest avoidance. Bonding is conceived of as the developmental foundation of a form of social attraction, here called "familial attraction," which is evolutionarily distinct from sexual attraction.

Cryptic Relatedness and the Opportunity for Kin Recognition in Microtine Rodents

Charnov and Finerty (1980) suggested that vole population density can be regulated by aggressive interactions that change with the relatedness of neighbors. As density increases, the relatedness of neighbors will decrease because of dispersal. Presumably, unrelated individuals will behave less amicably (more aggressively) toward one another. As density increases, dispersal will cause the relatedness of neighbors to decrease and therefore increase the levels of aggression in the population. Increased aggressive levels are postulated to cause the crash of numbers seen in vole population fluctuations. Inherent in this mechanism is the ability for voles to distinguish, and respond differentially between relatives and nonrelatives. As we will show, for this hypothesis to be correct, it must take into consideration cryptic relatedness, relatedness in which the members of the dyad cannot, in fact, determine that they are related. Familiarity, based on association prior to weaning, is the proximate cue that microtine rodents use to assess kinship (Blaustein et al. 1987a,b, Ferkin 1990). Familiar nestmates are recognized as close relatives, whereas unfamiliar nestmates are not identified as relatives (Schadler 1983, Gavish et al. 1984, Boyd and Blaustein 1985, Ferkin 1989, Ferkin and Rutka 1990). To date, there is no evidence to show that microtine rodents employ phenotype matching, recognition alleles, or the major histocompatibility complex to assess kinship (Yamazaki et al. 1980). Genetic relatedness, per se, plays no apparent role in kin recognition for microtine rodents (Bekoff 1981, Blaustein et al. 1987a,b, Ferkin 1990). Thus, the ability to assess genetic relatedness of unfamiliar relatives appears unlikely for microtine rodents. The persistence of kin recognition is dependent on repeated social contacts with close kin (Ferkin 1988, 1990). Although kin recognition and kin-directed behaviors, such as reduced agonism, sharing of nest sites, increased nepotism, and the avoidance of inbreeding, can operate without kin recognition if related individuals interact frequently (Hamilton 1964), repeated contacts with close relatives may not be a feature common to most microtine social organizations (Wolff 1985, Cockburn 1988). The opportunity to identify and be recognized as a close relative will be affected markedly by the type of mating system, population turnover rate, dispersal tendency, nesting patterns, and parental care displayed in a particular species. Therefore, the opportunity to identify and be recognized as a close relative will be affected markedly between microtine species. Microtine rodents that do not have protracted interactions with close relatives may not be able to recognize unfamiliar close relatives.

Mechanisms of kin recognition

Although kin recognition mechanisms are necessary neither for the operation of kin selection nor for optimal mate selection (e.g. inbreeding avoidance), once established, such mechanisms may accelerate the evolution of kin-directed behaviors. Aside from spatially-based recognition, in which organisms adjust their behavior principally in response to their immediate location, several behavioral mechanisms originally suggested by Hamilton recently have generated discussion and controversy. Familiar kin can be identified individually, but individual recognition mechanisms alone cannot serve to distinguish between closely and more distantly related kin, or to identify novel relatives. These kin can be identified through group recognition mechanisms that evaluate the extent of trait overlap among individuals to determine their probable genetic relatedness. Precisely whom an organism recognizes as kin using either type of mechanism may be dependent on its past social experience. Individual recognition permits discrimination of previously encountered conspecifics, whereas group recognition generally leads to discrimination of individuals sharing traits with previously encountered conspecifics. Individual and group recognition mechanisms are not mutually exclusive, and they may operate concurrently. Furthermore, they are not distinct, separable processes. Mistaken individual identifications become more likely as conspecifics show increasing phenotypic resemblance, and hence kin discrimination can result directly from individual recognition mechanisms. The extent to which kin are identified depends on a criterion rule which may fluctuate in response to social, spatial, and temporal factors. When favored by natural selection, kin recognition may be facilitated by the process of stimulus generalization, as trait matching is achieved within wider tolerance ranges. But such generalization may occur even in the absence of selection per se . Recognition effected through the action of hypothetical “recognition alleles” does not constitute a logical alternative to individual or group kin recognition mechanisms. In common with those processes, recognition allels must operate by the effective matching of phenotypes. Unlike kin recognition mechanisms, which assess similarity by generalized phenotypic comparisons, the phenotype compared by a recognition allele (or linkage group) is that it itself generates, leading to the possibility of intragenomic conflict. As suggested by Hamilton, alleles might be expected to induce their bearers to favor behaviorally conspecifics that share thier copies, regardless of the overall genetic relatedness of those conspecifics. Hence, recognition alleles, if they exist, would not invariably lead to kin identifications. Moreover, such alleles need not act in a manner that necessarily excludes learning. Through inbreeding experiments, a genetic component to the labels that elicit kin recognition has been demonstrated in some invertebrates. Genetically determined kin recognition templates, with which the labels are compared, have yet to be established. A “genetic recognition system” cannot be safely inferred when experiments fail to demonstrate experiential effects on recognition abilities. Kin recognition mechanisms can be characterized through detailed examination of the ontogenetic and sensory processes underlying recognition abilities, and of the ecological and social contexts in which kin-directed behaviors are expressed.