Source selection shapes the strength of cultural transmission pathways

Human culture depends on people learning from one another. Cultural evolutionary theory distinguishes three transmission pathways: learning from parents (vertical), non-parental adults (oblique), and peers (horizontal), which differ in how rapidly information spreads within and across generations. During middle childhood, children's social worlds expand beyond the family, creating opportunities for all three pathways to operate simultaneously, yet their relative strength has rarely been compared directly. Using 1,262 dyads of 6-13 year-olds and their parents, we examined the relative strength of vertical, oblique, and horizontal transmission in two complementary behavioral experiments. Participants either received information from, or chose between, their own parent or child, an unrelated adult or child, and a peer while completing an estimation task. This design allowed us to separate two components of cultural transmission: whom people choose to learn from and how strongly they use information once it has been acquired. Vertical transmission emerged as the strongest pathway. This advantage was driven primarily by source selection, as children and parents overwhelmingly selected one another as information sources, with parents learning from their own child providing evidence for reverse vertical transmission. Once information had been acquired, however, information weighting differed little between vertical, oblique, and horizontal transmission. Instead, developmental differences dominated: social information use declined markedly across middle childhood and remained consistently higher in children than in parents. Together, these findings suggest that the relative strength of cultural transmission pathways is determined primarily by source selection rather than information weighting.