Intrafamily and intragenomic conflicts in human warfare

Abstract

Recent years have seen an explosion of multidisciplinary interest in ancient human warfare. Theory has emphasized a key role for kin-selected cooperation, modulated by sex-specific demography, in explaining intergroup violence. However, conflicts of interest remain a relatively underexplored factor in the evolutionary-ecological study of warfare, with little consideration given to which parties influence the decision to go to war and how their motivations may differ. We develop a mathematical model to investigate the interplay between sex-specific demography and human warfare, showing that: the ecology of warfare drives the evolution of sex-biased dispersal; sex-biased dispersal modulates intrafamily and intragenomic conflicts in relation to warfare; intragenomic conflict drives parent-of-origin-specific patterns of gene expression—i.e. ‘genomic imprinting’—in relation to warfare phenotypes; and an ecological perspective of conflicts at the levels of the gene, individual, and social group yields novel predictions as to pathologies associated with mutations and epimutations at loci underpinning human violence.

The demography of human warfare can drive sex differences in altruism

“…'globally' (such that α i = 1 is fully local competition and α i = 0 is fully global competition). The scale of competition coefficient α i is modulated by a quantity M i = (1 -σ i )σ i , which describes the extent to which reproductive opportunities in a conquered group are obtained by a mixture of individuals from the winning and the defeated groups ('admixture', Micheletti et al 2017; see also Methods). For example, consider a case in which warfare is a purely male domain and thus leads to men from victorious groups reproducing in defeated groups, while women only compete in their home group (σ m > σ f = 0).…”

“…We employ a two-sex kin-selection model of between-group conflict, adapting and expanding a previously developed framework (Lehmann and Feldman 2008;Micheletti et al 2017Micheletti et al , 2018 to consider the evolution of altruism. We perform two analyses.…”

Adult sex ratios and partner scarcity among hunter–gatherers: implications for dispersal patterns and the evolution of human sociality

“…First, hunter -gatherers do not have a sex-specific dispersal pattern at sexual maturity [34,42 -44]. While hunter -gatherers and early humans were traditionally described as male philopatric [45,46], a characterization that persists in some fields [47], this claim has long been disputed and is not supported empirically [48][49][50][51][52][53]. The sex that disperses varies considerably across cultures (male, female, both or neither), with many groups expressing multiple patterns simultaneously [34,41,42,[54][55][56].…”

The Emergence of Egalitarianism in a Model of Early Human Societies

“…5D with 10 coalitions of approximately 150 individuals each). That is, assuming that oscillations are out-of-phase in different coalitions, coalitions in the cooperative phase would have an advantage in warfare over coalitions in the uncooperative phase, driving consolidation of human populations through conquest, as proposed previously (11,12,39).…”