Abstract
Parallels in anatomy between humans and domesticated mammals suggest that for the last 300,000 years, Homo sapiens has experienced more intense selection against the propensity for reactive aggression than other species of Homo. Selection against reactive aggression, a process that can also be called self-domestication, would help explain various physiological, behavioral, and cognitive features of humans, including the unique system of egalitarian male hierarchy in mobile hunter-gatherers. Here I review nine leading proposals for the occurrence of self-domestication in H. sapiens. To account for the domestication syndrome, proposals must explain what led to a decline in fitness of highly aggressive males, and why the explanatory factor applies only to H. sapiens and not to other species of Homo. The proposed explanations invoke genetic group selection; group-structured culture selection (also known as cultural group selection); social selection by female mate choice; social selection by male partner choice; increased self-control; cooperative breeding; high population density; use of lethal weapons; and language-based conspiracy. Most of these proposals face difficulties in accounting for the origins and/or maintenance of reduced reactive aggression. I conclude that the evolution of language-based conspiracy, which is a form of collective intentionality, was the key factor initiating and maintaining self-domestication in H. sapiens, because it is the most convincing mechanism for explaining the selective pressure against individually powerful fighters. Sophisticated language enabled males of low fighting prowess to cooperatively plan the execution of physically aggressive and domineering alpha males. This system is known today as a leveling mechanism in small-scale societies. Group-structured culture selection possibly accelerated the process.
Highlights
Darwin (1868) showed that domesticated mammals tend to share a variety of similarities in their appearance, anatomy and behavior, a phenotypic suite called the domestication syndrome
Based on the signals of human domestication found throughout the last 300,000 years, the species in which selection first occurred against male reactive aggression would have been the midPleistocene Homo that give rise to H. sapiens
This article is a first attempt to reconcile the anatomical evidence for self-domestication in H. sapiens with multiple theories about the evolution of prosocial and antisocial tendencies
Summary
Darwin (1868) showed that domesticated mammals tend to share a variety of similarities in their appearance, anatomy and behavior, a phenotypic suite called the domestication syndrome. The presence of a domestication syndrome appears to be a signal of selection again reactive aggression It is interesting, that evidence has recently been increasing for humans Homo sapiens having a domestication syndrome (Leach, 2003; Francis, 2015; Henrich, 2016; Hare, 2017; Hare and Wrangham, 2017; Theofanopoulou et al, 2017; Wilkins, 2017; Benítez-Burraco et al, 2018; Sánchez-Villagra and van Schaik, 2019; Wrangham, 2019). The Jebel Irhoud specimens have short faces, small teeth, and reduced brow-ridges compared to pre-sapiens ancestors, making them the earliest human specimens to show features of the domestication syndrome. These points suggest that Pleistocene Homo experienced selection for self-domestication starting before 300,000 years ago.
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