Two types of aggression in human evolution

Abstract

Two major types of aggression, proactive and reactive, are associated with contrasting expression, eliciting factors, neural pathways, development, and function. The distinction is useful for understanding the nature and evolution of human aggression. Compared with many primates, humans have a high propensity for proactive aggression, a trait shared with chimpanzees but not bonobos. By contrast, humans have a low propensity for reactive aggression compared with chimpanzees, and in this respect humans are more bonobo-like. The bimodal classification of human aggression helps solve two important puzzles. First, a long-standing debate about the significance of aggression in human nature is misconceived, because both positions are partly correct. The Hobbes-Huxley position rightly recognizes the high potential for proactive violence, while the Rousseau-Kropotkin position correctly notes the low frequency of reactive aggression. Second, the occurrence of two major types of human aggression solves the execution paradox, concerned with the hypothesized effects of capital punishment on self-domestication in the Pleistocene. The puzzle is that the propensity for aggressive behavior was supposedly reduced as a result of being selected against by capital punishment, but capital punishment is itself an aggressive behavior. Since the aggression used by executioners is proactive, the execution paradox is solved to the extent that the aggressive behavior of which victims were accused was frequently reactive, as has been reported. Both types of killing are important in humans, although proactive killing appears to be typically more frequent in war. The biology of proactive aggression is less well known and merits increased attention.

Evaluating the self‐domestication hypothesis of human evolution

“…In contrast to its sister‐group, the chimpanzees ( Pan troglodytes ), bonobos show several derived features that include depigmentation of lips and tail tufts, reduced canine dimorphism, and a smaller cranium—and thus brain size (Figure ). These features are hypothesized to have evolved as byproducts of selection (“spandrels” sensu Gould and Lewontin) for reduced aggressiveness, driven by the females' preference for mating with less aggressive males . The physiological response to social stress also differs between chimpanzees and bonobos: male chimpanzees exhibit testosterone reactivity, which reduces the potential for tolerance, whereas bonobos show increases in cortisol .…”

Subtypes of aggression and their relation to anxiety in Barbary macaques

“…By studying both types of aggression and their link to anxiety we contribute to the understanding of why primates behave aggressively and add comparative data for testing the idea that human RA and PA have evolutionary origins within non-human primates (Wrangham, 2017). Testing the cognitive predispositions of nonhuman primates and the severity of a perceived threat is a major methodological obstacle yet to be overcome.…”

Warfare in an evolutionary perspective

“…If aggressive access or monopolization of resources give benefits to individual fitness such propensity to act aggressively may be maintained over evolutionary time regardless of what the target of aggression is. Three traits play a key role in the evolution of aggression: (a) releasing of proactive aggression when ecological conditions favor aggression over peace; (b) assessing the fighting ability of the opponent(s) and of themselves; (c) categorization of individuals/groups as “friends” or competitors/enemies. These three traits are relevant for aggressive interactions both between members of the same group and between different groups.…”

“…The question of whether humans are innately peaceful or aggressive has fascinated scientists and philosophers for centuries . Wars, ethnic or religious contests, and intra‐group or intra‐family violence are scattered across historic periods and cultures, suggesting that aggression and violence are key aspects of human societies.…”

“…In the context of warfare, aggression is usually intra‐specific and inter‐personal, excluding other forms of aggression (e.g., slow violence; for in‐depth discussion on this see Reference ). Wrangham (see also Reference ) further differentiated between proactive aggression, a trait humans probably share with chimpanzees, and reactive aggression, which is more frequently observed in nonhuman primates and other animals but less frequently in humans.…”