Targeted conspiratorial killing, human self-domestication and the evolution of groupishness

Abstract

Groupishness is a set of tendencies to respond to group members with prosociality and cooperation in ways that transcend apparent self-interest. Its evolution is puzzling because it gives the impression of breaking the ordinary rules of natural selection. Boehm's solution is that moral elements of groupishness originated and evolved as a result of group members becoming efficient executioners of antisocial individuals, and he noted that self-domestication would have proceeded from the same dynamic. Self-domestication is indicated first at ~300,000 years ago and has probably gathered pace ever since, suggesting selection for self-domestication and groupishness for at least 12,000 generations. Here I propose that a specifically human style of violence, targeted conspiratorial killing, contributed importantly to both self-domestication and to promoting groupishness. Targeted conspiratorial killing is unknown in chimpanzees or any other vertebrate, and is significant because it permits coalitions to kill antisocial individuals cheaply. The hypothesis that major elements of groupishness are due to targeted conspiratorial killing helps explain why they are much more elaborated in humans than in other species.

Keywords: Execution hypothesis; chimpanzee; cooperation; morality.

Graphical abstract

Figure 1.

Hypothesised effects of targeted conspiratorial killing (TCK). The upper and lower pathways diagram the evolution of self-domestication and groupishness, respectively. Targeted conspiratorial killing is cheap because it can be conducted at low risk to the killers. It was putatively enabled by language becoming sufficiently sophisticated to foster conspiratorial behaviour. A positive feedback loop followed as a result of increases in features such as social tolerance, linguistic skills and tendencies for conformity, which made targeted conspiratorial killing increasingly easy to organise.

Figure 2.

Distribution of chimpanzees and bonobos. 1, Western chimpanzee, P. troglodytes verus; 2, Nigerian–Cameroonian chimpanzee, P. troglodytes ellioti; 3, central chimpanzee, P. troglodytes troglodytes; 4, eastern chimpanzee, P. troglodytes schweinfurthii; 5, bonobo, P. paniscus. P. troglodytes verus is separated from P. troglodytes ellioti by the Dahomey Gap, a region too dry to support forest. P. paniscus is separated from P. troglodytes schweinfurthii by the Congo River. Map is from Prüfer et al. (2012).

Figure 3.

Inferred population history of Pan and Homo, showing possible self-domestication events (starred). Ape phylogeny is from Prado-Martinez et al. (2013), who estimated the times of population splits. Homo phylogeny is from Schlebusch et al. (2017). No fossil data are available to help estimate the times of self-domestication in P. paniscus and P. troglodytes verus.