Signal traditions and cultural loss in chimpanzees

The horizontal transmission of cultural knowledge is a powerful mechanism of evolutionary change¹. Across taxa, group-specific cultural traditions are expressed in diverse contexts, such as foraging, tool use, self-care and socialization². These traditions arise when group members converge on specific behavioral phenotypes. When these behavioral phenotypes involve communicative signals, such as gestures, they are termed dialects³. However, gestural dialects are rare in non-humans³. Behavioral phenotypes and traditions can also be lost, a well-documented phenomenon in humans⁴, but rarely documented in non-human animals⁵. Here, we find that chimpanzee gestures produced in copulation solicitations show culturally established phenotypes and undergo cultural loss due to human-induced population decline.