RESUMO
Typical patterns of discriminative grandparental investment i.e. high investment provided by the maternal grandmother and low investment provided by the paternal grandfather, are mainly interpreted based on the "paternity uncertainty hypothesis". Accordingly, especially paternal grandfathers are confronted with a double risk of investing in genetically unrelated grandchildren. The present study focuses on the impact of phenotypic resemblance between parents and grandparents on grandparental investment. 94 female and 83 male participants aged 19 to 40 years (x = 27.4; SD = 5.8) were enrolled in the retrospective analysis. An online questionnaire, specifically developed for this study, was used for data collection. In line with predictions, the highest investment, contact frequency and best relationship were found for maternal grandmothers, while paternal grandfathers showed the lowest investment patterns. Phenotypic resemblance between parents and grandfathers enhanced grandfathers' investment significantly, but resemblance had no effect in the case of maternal grandmothers. We conclude that phenotypic similarities can be interpreted as indicators of genetic relatedness and therefore increase grandparental investment among those grandparents, who are confronted with paternity uncertainty, i.e. paternal grandmother and maternal as well as paternal grandfather.