The Evolutionary Roots of Familial Altruism

Paternity Uncertainty Shapes Patterns of Kindness

Bibliographic Data

ID7154121
AuthorsRadim Kuba (0000-0001-9614-9675, Charles University, corresponding author), Jaroslav Flegr (0000-0002-0822-0126, Charles University)
Year2025
Volume23
Issue3
Pages14747049251357493-14747049251357493
Publication date2025-07-01
Peer ReviewedYes
Open AccessYes
TypeARTICLE
VenueEvolutionary Psychology (JOURNAL)
Journal identifiersISSN: 1474-7049 • E-ISSN: 1474-7049
PublisherSAGE Publications Inc (PUBLISHER)
DOI10.1177/14747049251357493
PMID40635502
OpenAlexW4412155091
LanguageEN
References cited64

We investigated how paternity uncertainty (PU) shapes perceptions of familial kindness. We predicted that relatives with lower PU would be rated as kinder than those with higher PU. A total of 9,128 participants rated the kindness of specific relatives in their families. Main analyses focused on parents and maternal/paternal grandparents, who differ in their typical levels of PU. Siblings were included for broader within-family comparisons, while step-relatives, all having identical (maximal) PU, served as negative controls. Controlling for sex, age, and random effects of raters and targets, results supported PU predictions: PU showed a negative correlation with rated kindness ( β = –0.148, t (31,910) = –6.23, p χ 2 (2) = 42.84, p p d = 0.15; 1 vs. 2: p = 0.0002, d = 0.08). Mothers and maternal grandmothers (no PU) were rated the kindest, while the paternal grandfather (two PU) was rated lowest. Daughters consistently rated their biological parents higher than sons, possibly reflecting lower PU through female offspring. Maternal grandfathers were rated kinder than fathers, despite identical PU, perhaps due to redirected investment by non-reproducing elders. Furthermore, mothers were rated kinder than maternal grandmothers, possibly due to “insider knowledge” of their children's paternity. Step-relatives showed minimal variation, suggesting that observed differences among biological kin reflect genetic relatedness and PU, rather than non-genetic factors. Overall, our findings support kin selection theory and suggest that paternity uncertainty subtly yet systematically shapes perceptions of familial kindness

Kindness · Political science · Attachment and Relationship Dynamics · Evolutionary Game Theory and Cooperation · Evolutionary Psychology and Human Behavior · Law · Psychology · Social Psychology

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