Male relatives benefit more from kin selecting tendencies enhancing social status

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Kruger, D.J. (1998, May). Relative worth across disparate types of assistance. Poster session presented at the annual meeting of the Midwestern Psychological Association, Chicago. Data available on-line:


This paper suggests a link between kin selecting tendencies and human mate selection criteria. Kin selection was evident for assistance impacting survival/health, material wealth, and social status. The kin selecting effect was stronger for male targets than for female targets with benefits enhancing social status, which males are valued for in sexual selection.

Psychologists researching helping and altruism have argued against the existence of kin selecting effects (e.g., Batson, 1997) and others studying sex roles have decried sex-specific mate selection criteria (e.g., Eagly & Wood, 1999). This study investigated tendencies for kin selection, and whether sex-specific mate selection criteria would increase the kin selecting effect for male relatives.

Despite Herbert Spencer's catch phrase "survival of the fittest," the ultimate criterion that determines if a genetic tendency for altruism spreads is whether it benefits the genes themselves, not whether it benefits the bearer of the genes (Hamilton, 1964a). Hamilton's inclusive fitness theory (1964b) predicts that a genetically influenced tendency to help relatives is likely to spread across a population when the cost in reproductive fitness to the donor is less than the product of the fitness benefit to the recipient(s) and the proportion of genes not common to the species that the donor and recipient(s) share.

Empirical evidence supports the existence of kin selecting behaviors in humans (Essock-Vitale & McGuire, 1985; Shavit, Fischer, & Koresh, 1994) and the psychological processes that may facilitate them (Korchmaros & Kenney, 2001; Kruger, 2001). Burnstein, Crandall and Kitayama (1997) demonstrated how kin selecting tendencies could be affected by certain qualities of kin with equivalent genetic distance. Burnstein et al. (1997) found that respondents were (a) more likely to help infants and the elderly in everyday situations but were more likely to save young targets (1, 10 and 18 years) than older targets (45 and 75 years) in life-or-death situations, (b) under famine conditions, more likely to save 10 and 18 year olds than those of other ages, (c) more likely to help kin in poor health in everyday situations, but healthy kin in life-or-death situations, and (d) more likely to help poor kin in everyday situations but wealthy kin in life-or-death situations. This demonstrates that kin selecting effects may be moderated by factors relevant to survival and reproductive success.

Characteristics preferred in mates reflect the roles that males and females take in successful human reproduction. There are many characteristics that both sexes value in a potential mate; including kindness, understanding and intelligence (Kenrick & Simpson, 1997). Humans also have sex-specific mate selection criteria. In a cross-cultural study, Buss (1989) found that men value potential female partners for indicators of fecundity, the ability to produce and care for children. Women value prospective male suitors on a cluster of characteristics related to resource potential: good financial prospects, ambition, industriousness, older age, and emotional maturity. Human males contribute substantially more to the provision and care of offspring than most other species (Fisher, 1992). Thus, females select for males with higher social status and access to resources, ones who could successfully provide for them and their developing offspring.

Some have criticized the evolutionary explanation for human mate selection criteria and offer a cultural explanation. Eagly and Wood (1999) propose that men monopolize the means of production and exhibit social dominance in the societies under study. Thus, women are only maximizing utility by selecting men with substantial resources or resource potential, given the constraints of society.

If mate selection criteria are socially constructed, the favored attributes should reverse gender assignments when females have more power and resources. However, in societies where women have more economic resources than men, the pattern is consistent (Ardener, Ardener, & Warmington, 1960). In fact, when women in modern post-industrial societies hold positions of high status and economic power, their preferences for high status men appear to increase in strength (Buss, 1989; Townsend, 1989; Wiederman & Allgeier, 1992). Also, men in all cultures tend to seek mates near their own age when they are young and seek progressively younger women as they age. Yet, contrary to socio-cultural power explanations for mate selection criteria, teenage males are attracted to substantially older women (Kenrick & Simpson, 1997).

Reversal in criteria association does occur in species where males make the greater parental investment, such as seahorses, certain frogs, the Mormon cricket, and several species of marsh birds. In these species, females compete among themselves for access to males (Crawford, 1998; Trivers, 1985). Female seahorses typically have brightly colored ornamentation, in contrast to the dull males. Seahorse females competing for the attention of males contrast with the more common pattern of brightly ornamented males and camouflaged females exemplified by peacocks and peahens.

The current study examines psychological processes facilitating kin selection and their relationship to mate selection criteria. Kin selection is hypothesized to be stronger for male targets on material wealth and social status, criteria males are valued for in sexual selection. It is difficult to imagine gender-neutral forms of assistance increasing the attractiveness of the physical indicators of female fecundity, other than guaranteeing frequent exercise and a healthy diet. Thus, items affecting survival and health were used. These items approximate the typical scenarios used to describe and study kin selecting behaviors. Because survival and good health is necessary for both genders, responses for this area were not predicted to exhibit gender specificity. Actions leading to pleasant and unpleasant experiences were used as a comparison condition. Kin selection is expected to be weaker for these actions, which do not significantly impact survival or reproduction. Experience items are also not expected to show sex-specificity in kin-selection.


Ethnically diverse undergraduate students (N=96, female = 64) at an urban Midwestern American university completed a questionnaire containing 65 scenarios with a choice between two options. Participants indicated the direction and strength of their decision by circling the appropriate point on an unnumbered 21-point bipolar scale. Filler items asked participants to make to decisions on a variety of situations, such as what type of vehicle to buy and where to go on vacation. Four critical items measured responses in each of four domains of assistance: tangible resources, social status, survival/health, and pleasant/unpleasant experiences. Each domain contained two items where the selected individual would have better outcomes and two items where the selected individual would fare worse.

Eight questionnaire forms matched each scenario with eight pairs of named individuals. The pairs varied by sex and difference in relatedness: Sibling (brother/sister) vs. nibling (nephew/niece), nibling vs. cousin, sibling vs. friend, and nibling vs. friend. Targets were matched for sex in each pair. The position of targets rotated by form across scale anchor position, and all positions were reversed halfway through the data collection. Locations circled on the 21-point scale were converted into scores from -10 to +10. Overall scores for each type of scenario summed the scores from the positive items and subtracted the scores from the negative items.

A 4 (scenario type) x 4 (pair type) x 2 (sex) repeated measures ANOVA analyzed the data. Kin selection was strongest for tangible resource scenarios, and declined across life/health scenarios, social status scenarios, and experience scenarios, F(3,264) = 4.25, p < .01. Kin selection was strongest for choices between sibling and friend, decreasing across sibling vs. nibling, nibling vs. friend, and nibling vs. cousin, F(3,88) = 10.38, p < .001. Significant interactions occurred between target gender and scenario type, F(3,264) = 4.29, p < .01, and between the difference in relatedness and type of scenario, F(9,264) = 4.97,p < .001. The closer relation was favored in the majority of all scenarios.

Kin selection was significantly stronger for male targets than for female targets in social status scenarios, t(94) = 3.42, p < .001. Linear contrasts indicated that comparisons with sibling targets exhibited stronger kin selection than those without sibling targets for tangible resources, F(1,92) = 10.71, p < .01, social status, F(1,92) = 16.28, p < .01, and pleasant/unpleasant experiences, F(1,92) = 10.68, p < .01.


The results provide further evidence for psychological processes facilitating kin selection. Closer kin tended to be favored for assistance aiding survival and health, building tangible financial resources, and enhancing social status. Kin selection was strongest for siblings, which is expected considering their genetic proximity. The comparison condition of pleasant and unpleasant experiences provided divergent validity, kin selection was weaker for these scenarios and did not differ by target sex. The use of negative and positive scenarios required that participants not only favor the closer relative with beneficial assistance, but also direct negative consequences towards more distant kin or non-kin, providing a strong test for the experimental hypotheses.

Participants more strongly favored their closer male relatives in intentions to provide assistance enhancing social status. This effect cannot be due to socially constructed norms favoring males. Both of the target characters for each scenario were either female or male, there were no choices between male and female targets. Also, the social status items were balanced across situations sometimes associated with specific gender roles.

No effect of sex was found for kin selecting actions enhancing material wealth. This was unexpected considering the historical tendency for males to inherit the bulk of wealth and property. One possible explanation is the certainty of motherhood, relative to paternal uncertainty. Material assistance to female relatives may have been a reliable method of enhancing inclusive fitness during human evolutionary history.

Most studies of kin selection focus on rescue scenarios. The domains of material wealth and social status also exhibited kin selection, providing new directions for future research in this area. The results support the existence of kin selecting tendencies and mate selection criteria in humans, and suggest a possibly unique interaction between these two evolutionary processes.


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