According to a large study published in Evolutionary Psychology, people consistently perceive family members as kinder when there is greater certainty of biological relatedness. Humans often assume that kindness within families is driven mainly by love, shared history, or cultural expectations. Yet evolutionary theories suggest that altruism within families may also be shaped by genetic relatedness. According to kin selection theory, people are predisposed to invest more care and support in relatives who are more likely to share their genes, because such investment indirectly promotes their own genetic success. One important factor complicating this picture is paternity uncertainty, the fact that, unlike maternity, biological fatherhood is never absolutely certain. Radim Kuba and Jaroslav Flegr examined whether this uncertainty influences how people perceive kindness among different family members. Drawing on evolutionary psychology and prior findings on parental and grandparental investment, they asked whether relatives associated with higher paternity certainty (such as mothers or maternal grandmothers) are consistently seen as kinder than those associated with lower certainty (such as paternal grandfathers). The researchers analyzed data from a …