The Evolution of Competition

Human competition is, at least partially, responsible for some of the transcended achievements of the species (walking on the moon, the polio vaccine, etc.), but the forces unleashed by competition have also led to profound human suffering (warfare, domination of one group by another group, etc.). In this article, the authors approach competition from an evolutionary perspective, applying Darwin’s theories of natural and sexual selection to understand better the nature of human competition. From the perspective of evolutionary psychology, humans engage in competition to gain resources, including status, food, and mating opportunities. Males tend to engage in more overt and aggressive forms of competition than females, but both sexes desire access to material and cultural goods associated with reproductive fitness. In the last roughly seventy years, the nature of men’s competition has transformed dramatically leading to declines in both within and between-group violence. As developed societies have succeeded in suppressing more overt and destructive forms of male–male competition, men attempt to gain status through occupational success, cognitive sophistication, moral signaling, and other relatively nonviolent behaviors. In this sense, men’s and women’s competition is more similar than it was a century ago. However, women’s competition is still less visible and relies on more indirect mechanisms (e.g., spreading gossip, subtle use of body language). For this reason, female–female competition has attracted less study than male–male competition. Fortunately, in the last decade, psychologists have partially redressed this imbalance.

No evidence that relatedness or familiarity modulate male harm in wild Drosophila melanogaster

Sexual selection frequently promotes the evolution of aggressive behaviours that help males compete against their rivals, but which may harm females and hamper their fitness. Kin selection theory predicts that optimal male-male competition levels can be reduced when competitors are more genetically related to each other than to the population average, contributing to resolve this sexual conflict. Work in Drosophila melanogaster has spearheaded empirical tests of this idea, but studies so far have been conducted in lab-adapted populations in homogeneous rearing environments that may hamper kin recognition, and used highly skewed sex ratios that may fail to reflect average natural conditions. Here, we performed a fully factorial design with the aim of exploring how rearing environment (i.e. familiarity) and relatedness affect male-male aggression, male harassment, and overall male harm levels in a natural population of Drosophila melanogaster, under more natural conditions. Namely, we: a) manipulated relatedness and familiarity so that larvae reared apart were raised in different environments, as is common in the wild, and b) studied the effects of relatedness and familiarity under average levels of male-male competition in the field. We show that, contrary to previous findings, groups of unrelated-unfamiliar males were as likely to fight with each other and harass females than related-familiar males, and that overall levels of male harm to females were similar across treatments. Our results suggest that the role of kin selection in modulating sexual conflict is yet unclear in Drosophila melanogaster, and call for further studies that focus on natural populations and realistic socio-sexual and ecological environments.

Domains of Female Choice in Human Evolution

The present article advances the view that women’s mate preferences can be grouped into at least two overarching domains: competitiveness and fatherhood. Theoretical and empirical considerations suggest that female mate preferences evolve in contexts of male competitiveness and often amplify the effects of male-male competition. Evidence for the importance of male-male competition and female choice for competitiveness in humans is reviewed. Evidence is likewise offered for the importance of human fatherhood as an additional domain of female choice outside of male competitiveness. Implications of more inclusive mate preferences for the evolution of cognitive architecture are discussed.

Runaway evolution from male-male competition

Understanding why and how elaborated traits evolve remains a fascination and a challenge. Darwin proposed both male-male competition and female mate choice as explanations for elaboration because such traits are often mediators of social interactions that govern access to mates. Although we have robust evolutionary quantitative genetic models for how mate choice can lead to runaway evolution, we lack an equivalent framework for understanding how male-male competition can drive extreme elaboration of traits. Here, we integrate the logic of optimality models into the quantitative genetic framework of interacting phenotypes to fill this gap. We assume that males modulate their aggression based on the relative size of a trait that signals willingness and ability to fight and identify conditions where the signal undergoes rapid and exponential evolution. Males receive fitness benefits from winning contests, but they may accrue fitness costs due to threats imposed by their opponent. This cost leads to a force of social selection that accelerates as the signaling trait is elaborated, which may cause runaway evolution of the signal. Even when a runaway is checked by natural selection, we find that signaling traits evolving by male-male competition can be elaborated well beyond their naturally selected optimum. Our model identifies simple conditions generating feedback between the behavioral and morphological traits mediating male-male competition, providing clear testable predictions. We conclude that, like the well-characterized case of female mate choice, male-male competition can provide a coevolving source of selection that can drive a runaway process resulting in evolution of elaborate traits.

Increased male mating success in the presence of prey and rivals in a sexually cannibalistic mantis

Precopulatory sexual cannibalism—or cannibalism without mating—is expected to promote the evolution of male strategies that enhance mating success and reduce the risk of cannibalism, such as preferentially approaching feeding females. Sexual selection on male competitiveness has the potential to alter male mating decisions in the face of cannibalism risk, but such effects are poorly understood. We investigated the effect of prey availability and male–male competition on mating incidence in the highly cannibalistic Springbok mantis, Miomantis caffra. We found that matings were initiated more rapidly and more often in the presence of prey, suggesting that females distracted with foraging may be less of a threat. Competition between males also hastened the onset of copulation and led to higher mating success, with very large effects occurring in the presence of both prey and competitors, indicating that intrasexual competition may intensify attraction to foraging females. Taken together, our results suggest that precopulatory cannibalism has selected for male preference for foraging females and that males adjust their mating strategy to both the risk of competition and the threat of cannibalism.