12/23/2023 0 Comments Chimpanzee hand groom clasp![]() We support the view that a detailed look at the behavioural differences between groups beyond a mere present/absent distinction is necessary to reveal a species' capacity and tendency to adopt a group-specific behavioural variant. While McGrew & Tutin's arguments have been adopted by later researchers investigating GHC behaviour in chimpanzees, the core question of whether this particular social behaviour can be validly considered ‘cultural’ has escaped closer empirical scrutiny. This line of reasoning led the authors to conclude that the GHC behaviour contains the necessary prerequisites for it to be considered ‘cultural’. In their influential paper, McGrew & Tutin elaborate on the importance of this finding by arguing that this present/absent distinction cannot be explained by genetic predispositions nor by environmental factors. This claim was based on the observation that the chimpanzees of the K(ajabala)-group in the Tanzanian Mahale mountains engaged in a peculiar social behaviour in which two individuals extend one arm overhead and clasp each other's upraised hands while grooming each other with the other arm, while the well-studied chimpanzees of the nearby Gombe field site were never observed engaging in it. Grooming handclasp (GHC) behaviour was the first social behaviour to be described as a ‘social custom’ in chimpanzees. These results strongly indicate that chimpanzees' social behaviour is not only motivated by innate predispositions and individual inclinations, but may also be partly cultural in nature. GHC has been part of the behavioural repertoire of the chimpanzees under study for more than 9 years (surpassing durability criterion) and spread across generations (surpassing expansion criterion). Critically, GHC style (defined by points of bodily contact) could be systematically linked to the chimpanzee's group identity, showed temporal consistency both within and between groups, and could not be accounted for by the arm-length differential between partners. Ninety chimpanzees were studied for a total of 1029 h 1394 GHC bouts were observed between 20. Here, we measured (i) variation, (ii) durability and (iii) expansion of the GHC behaviour in four chimpanzee communities that do not systematically differ in their genetic backgrounds and live in similar ecological environments. To date, however, the validity of this claim and the extent to which this social behaviour varies between groups is unclear. These results suggest that not all socially learned cultural behaviors are acquired in the way of learning tool use.Grooming handclasp (GHC) behaviour was originally advocated as the first evidence of social culture in chimpanzees owing to the finding that some populations engaged in the behaviour and others do not. For example, infants did not try to perform GHC initially instead, mothers were more active in the earliest stages. Overall, the ontogeny of GHC showed several dissimilarities with that of tool use and was more an extension of the development of typical grooming behavior. ![]() GHC by young chimpanzees was shorter in duration than that among adults. Young males were observed to perform GHC with larger numbers of partners than were young females. By gradually expanding GHC partners from the mother to other females and then to males, chimpanzees increased the number of GHC partners with age. However, some orphans engaged in GHC earlier than nonorphans. The first performances of GHC with nonrelated females were at around age 9 years, and those with adult males at around 11 years. First performances of GHC with the mother were observed at around 4-6 years old the earliest observed age was 4 years and 4 months old. We have collected 383 cases of GHC where at least one of the participants was 15 years old or younger during 1994-2007. ![]() Thus, in this study, we describe the developmental process of the grooming hand-clasp (GHC), one of the well-known social customs of chimpanzees at Mahale. However, few studies have examined the ontogeny of social customs that do not require complex skills. Among cultural behaviors of chimpanzees, the developmental processes of complex skills involved in tool use are relatively well known.
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