Kin investment biases of aunts and uncles: associations with phenotypic resemblance and sociodemographic characteristics.

Abstract

Higher investment in maternal than paternal aunts and uncles is explained by the "paternity uncertainty hypothesis". Regardless of laterality, however, aunts show a greater degree of investment than uncles, which is attributed to sex-specific reproductive strategies. Resemblance cues can be used as indicators of genetic relatedness. The central hypothesis of the current study was that perceived phenotypic resemblance between aunts/uncles and niblings would be associated with aunts' and uncles' investment. The association was predicted to be stronger with respect to patrilateral than matrilateral aunts and uncles and stronger with respect to patrilateral aunts than patrilateral uncles. 243 Iranians aged between 15 and 50 participated in a retrospective analysis and filled out a 52-item questionnaire focusing on the solicitude, emotional closeness, and contact frequency between aunts/uncles and their nephews/nieces. In addition, the participants had to rate their phenotypic resemblance with their aunts and uncles. Aunts' and uncles' solicitude, emotional closeness, and contact frequency were differentially expressed according to sex and laterality. Maternal aunts showed the significantly highest emotional closeness, contact frequency, and investment, while the opposite was true for paternal uncles. Moreover, investment was correlated with phenotypic resemblance. Such association was stronger for patrilateral than matrilateral aunts and uncles, and concerning solicitude it was stronger for patrilateral aunts than patrilateral uncles. The resemblance-based kin recognition mechanism among aunts and uncles was self- rather than family-referent. In conclusion, phenotypic similarity can be used as a cue to genetic kinship and is correlated with the investment of aunts and uncles. However, such associations also depend on the degree of genetic relatedness and the differential kin investment provided by each sex.