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.

Keywords: genomic imprinting; intragenomic conflict; parent–offspring conflict; sex-biased dispersal; sexual conflict; war.

Figure 1.

Evolution of sex-biased dispersal and migration. Convergence-stable levels of female dispersal (, solid orange line), male dispersal (, solid purple line), female migration (, dashed orange line), and male migration (, dashed purple line) as functions of cost of male dispersal (λ_m; (a); other parameter values are λ_f = 0.05, s_f = 1, s_m = 0, N_f = N_m = 10, ) and the probability that a conquered male obtains a breeding spot (s_m; (b); other parameter values are λ_f = λ_m = 0.05, s_f = 1, N_f = N_m = 10, ). (Online version in colour.)

Figure 2.

Intrafamily conflicts over belligerence and bravery. Convergence-stable levels of belligerence (A*, (a)) and bravery (Ω*, (b)) as functions of female migration (m_f) when belligerence is controlled by the focal male's father (blue line), his mother (orange line), or the focal male himself (green line). Other parameter values are ((a) only), ((b) only), m_m = 0.5, s_f = 1, s_m = 0, N_f = N_m = 10. We assume functional forms a = A_att and t = 1–0.025 a² (a), and ω(Ω_att, Ω_def) = ½ (1 + Ω_att – Ω_def) and τ = 1 – 0.025 Ω² (b). (Online version in colour.)

Figure 3.

Intragenomic conflicts over belligerence and bravery. Convergence-stable level of belligerence (A*, (a)) and bravery (Ω*, (b)) as functions of female migration (m_f) when belligerence or bravery are controlled by the focal individual's paternal-origin genes (blue line), maternal-origin genes (orange line), or unknown-origin genes (green line). Other parameter values are ((a) only), ((b) only) and m_m = 0.5, s_f = 1, s_m = 0, N_f = N_m = 10. We assume functional forms a = A_att and t = 1–0.025 a² (a), and ω(Ω_att, Ω_def) = ½ (1 + Ω_att − Ω_def) and τ = 1–0.025 Ω² (b). (Online version in colour.)

Figure 4.

Genomic imprinting and associated pathologies. Predicted patterns of parent-of-origin-specific gene expression and concomitant phenotypes for loci that are either promoters or inhibitors of belligerence (a) or bravery (b), under normal conditions and also as a result of three different mutational or epimutational perturbations: gene deletion, imprinting disruption, or uniparental disomy. Genes are either of maternal-origin (orange) or paternal-origin (blue) and are either silenced (crosses) or expressed (arrows). Human figures from the George Stow collection at Iziko South African Museum, derived from The Digital Bleek and Lloyd (http://lloydbleekcollection.cs.uct.ac.za/) with permission. (Online version in colour.)