biostudies-literaturevan Boekholt BNational Geographic SocietyEuropean Research CouncilNational Science Foundation Graduate Research Fellowship Program64https://www.ebi.ac.uk/biostudies/studies/S-EPMC11450076biostudies-literatureUnknown27(1)One promising method to tackle the question, "In which modality did language evolve?" is by studying the ontogenetic trajectory of signals in human's closest living relatives, including chimpanzees (Pan troglodytes). Concerning gestures, current debates centre on four different hypotheses: "phylogenetic ritualization", "social transmission through imitation", "ontogenetic ritualization", and "social negotiation". These differ in their predictions regarding idiosyncratic gestures, making such occurrences a crucial area of investigation. Here, we describe a novel and potential idiosyncratic behaviour - 'hand-on-eye' - which was initially observed in one mother-infant dyad in a community of chimpanzees living in the wild. We systematically investigated the form, sequential organisation, intenAnimal cognitionIdiosyncratic gesture use in a mother-infant dyad in chimpanzees (Pan troglodytes schweinfurthii) in the wild.PMC11450076772000, TurnTaking724608DGE 2137429EC-56837R-19Lahiff NJLee KCClark ISlocombe KEWilke Cvan Boekholt BPika SfalseIdiosyncratic gesture use in a mother-infant dyad in chimpanzees (Pan troglodytes schweinfurthii) in the wild.One promising method to tackle the question, "In which modality did language evolve?" is by studying the ontogenetic trajectory of signals in human's closest living relatives, including chimpanzees (Pan troglodytes). Concerning gestures, current debates centre on four different hypotheses: "phylogenetic ritualization", "social transmission through imitation", "ontogenetic ritualization", and "social negotiation". These differ in their predictions regarding idiosyncratic gestures, making such occurrences a crucial area of investigation. Here, we describe a novel and potential idiosyncratic behaviour - 'hand-on-eye' - which was initially observed in one mother-infant dyad in a community of chimpanzees living in the wild. We systematically investigated the form, sequential organisation, inten2024-01-01T00:00:00Z2024 Oct2025-04-04T01:54:34.314Z2025-04-04T01:54:34.314ZS-EPMC114500763936312610.1007/s10071-024-01904-3