Intra-community infanticide in wild, eastern chimpanzees: a 24-year review

Abstract

Infanticide is well documented in chimpanzees and various hypotheses have been proposed to explain this behavior. However, since infanticide by chimpanzees is relatively rare, it has thus far not been possible to thoroughly test these hypotheses. Here we present an analysis of the largest dataset of infanticides from a single community of chimpanzees, a full record of all intracommunity infanticides and failed attempts at infanticide over a 24-year period for the Sonso community of chimpanzees in the Budongo Forest, Uganda. We use these data to test four hypotheses for this behavior: the sexual selection hypothesis, male mating competition, resource competition, and meat acquisition. Our dataset consisted of 33 attacks on 30 victims, 11 of which were 'definite' infanticides, four of which 'almost certain', and nine were 'suspected', while nine were 'attempted' infanticides. The majority of attacks where the perpetrators were known (23) had only male attackers and victims were disproportionately young (two-thirds of victims with known ages were under 1 week old). Our data best support the sexual selection hypothesis for infanticide. Cannibalism was infrequent and partial, suggesting meat acquisition was a by-product of infanticide, and there was no evidence to suggest that infanticide was part of a male strategy to eliminate future competitors. Infanticide by females was rare, but we suggest sexual selection, operating through intra-sexual competition, may also be responsible for infanticide by females.

Maternal cannibalism in two populations of wild chimpanzees

“…It is thus possible that MON's or WAN's behavior could also be related to the nutritional benefits of meat consumption. However, given the large number of documented infant deaths in wild communities that do not lead to maternal cannibalism, or indeed cannibalism of any kind (Lowe et al 2019;Wilson et al 2014), we find this an unpersuasive explanation. Future research, however, could examine the abnormal environment hypothesis via noninvasive monitoring of urinary C-peptides as a proxy for nutritional stress (Wessling et al 2018).…”

“…Chimpanzee maternal responses to infant deaths are typically characterized by affiliation and carrying of the corpse, not by cannibalization (Biro et al 2010;Cronin et al 2011). Indeed, of the 26 direct observations of intra-community infanticide in chimpanzees recorded across several field sites and populations, none was reported to be associated with maternal cannibalism (Lowe et al 2019;Wilson et al 2014; Hobaiter pers. comm.…”

A machine learning approach to infant distress calls and maternal behaviour of wild chimpanzees

“…This potentially fitness enhancing ability can be particularly important in a species in which infanticide by both males and females is commonly reported (Arcadi and Wrangham 1999;Watts and Mitani 2000;Townsend et al 2007;Lowe et al 2019Lowe et al , 2020.…”

Female Dispersion Is Necessary, But Not Sufficient, For The Evolution of Monogamy in Mammals

“…What those advantages might be have not been explored here. The only two costs known to be high for anthropoids that might function as a countervailing benefit are predation risk (Cheney & Wrangham 1987;Isbell 1994;Shultz et al 2004;Shultz & Finlayson 2010;see also Burnham et al 2012) and infanticide risk (van Schaik & Dunbar 1990;van Schaik & Kappeler 1997;Borries et al 2011;Opie et al 2013;Lukas & Huchard 2014;Lowe et al 2019). Predation risk must play some role, since it is the principal driver for group-living in primates (Shultz et al 2004;Shultz & Finlayson 2010).…”