Emergence, propagation or disappearance of novel behavioral patterns in the habituated chimpanzees of Mahale: a review

Abstract

Each local population of chimpanzees shows cultural variation, but little is known about how behavioral variations first emerge, and how often variants spread to other individuals and then become fixed as a local culture in chimpanzee society. Although field studies of chimpanzees are still too short to answer these questions definitively, it may stimulate further study in various sites to summarize the developments observed over the past 40 years at Mahale, Tanzania. Innovative patterns were operationally defined as new behavioral patterns performed by M group chimpanzees from 1981 onwards. Innovations included patterns of feeding (n = 8), human-directed behavior (n = 3), hygiene behavior (n = 4), maternal carrying of infants (n = 2), courtship (n = 2), play (n = 6), intimidation displays (n = 3), and quasi-grooming (n = 4). Although most patterns were repeated later by other individuals, six patterns were never seen performed by another individual, and eight patterns were performed by one or a few individuals but social transmission was unlikely. Thus, innovation was not rare, but emergence of fashion or establishment of traditions seems to occur rarely in chimpanzee society.

Older, sociable capuchins (Cebus capucinus) invent more social behaviors, but younger monkeys innovate more in other contexts

“…Most groups have a current repertoire of bond-testing signals that have been steadily practiced by a subset of the group for many years, and these behaviors are not, for the most part, scored as innovations in this dataset, because they first appeared in the buffer period or even earlier. Food choice innovations (not reported here because of the interobserver reliability challenge of being able to correctly identify plants the first time that they are eaten) tend to be adopted quickly and remain in repertoires for long periods of time, such as is the case for chimpanzees (42) and various species of monkeys (29). Particularly useful food processing or drinking techniques, once invented, are likely to persist in repertoires for many years [or even centuries (43)].…”

<Note> Mahale Chimpanzees Start to Eat Oil Palm

“…Most of novel behavioral patterns have not spread to many other individuals 7 , so it is difficult to predict whether this novel food item will become a cultural food for the Mahale chimpanzees. A follow-up survey will be required.…”

“…In contrast, the Semliki chimpanzees in Uganda appear not to eat any part of the oil palm 5 . Researchers have observed the Mahale chimpanzees in Tanzania since the 1960s and have not observed these chimpanzees eating any part of the oil palm 6,7 , but in 2010 they started to eat the pith of the oil palm. This paper presents two observations of oil palm eating and discusses the triggers for this behavior.…”

<Note>Case study of an unusual human–chimpanzee conflict at Bulindi, Uganda

“…Consequently, the apes have ample opportunity to see their reflections in water. Young chimpanzees at Mahale were observed examining their reflections in pools and streams 9 , but it is not yet known if similar behavior occurs at Bulindi. Although the males at times intently examined the door, their high state of arousal implies that they most likely saw 'other' chimpanzees behind the glass.…”