Vertebrates show two major classes of sexually dimorphic traits: weaponry and ornaments. However, Darwin could not explain why their expression varies so much across lineages. We argue that coercion-avoidance can explain both the existence and taxonomic distribution of ornaments. Females maximize their fitness when they can freely choose their mates, but males are expected to use sexually dimor...

We used controlled aviary experiments to study the role of male ornaments in male-male competition and female choice in the common yellowthroat Geothlypis trichas, a sexually dichromatic warbler. Previous aviary studies in Wisconsin, USA, indicated that males with larger black facial masks were dominant over males with smaller masks and preferred by females in mate choice experiments. In this s...

Genetic models of the handicap theory of sexual selection propose that ornaments signal heritable male quality, so females mating with the most ornamented males acquire fitness benefits for their offspring. Male ornaments are predicted to have co­ evolved with female preference to be larger, and so more costly. The key prediction made by the handicap hypothesis is that male sexual traits have e...

The selection pressures by which mating preferences for ornamental traits can evolve in genetically monogamous mating systems remain understudied. Empirical evidence from several taxa supports the prevalence of dual-utility traits, defined as traits used both as armaments in intersexual selection and ornaments in intrasexual selection, as well as the importance of intrasexual resource competiti...

Why are traits that function as secondary sexual ornaments generally exaggerated in size compared to the naturally selected optimum, and not reduced? Because they deviate from the naturally selected optimum, traits that are reduced in size will handicap their bearer, and could thus provide an honest signal of quality to a potential mate. Thus if secondary sexual ornaments evolve via the handica...

The transition to farming is the process by which human groups switched from hunting and gathering wild resources to food production. Understanding how and to what extent the spreading of farming communities from the Near East had an impact on indigenous foraging populations in Europe has been the subject of lively debates for decades. Ethnographic and archaeological studies have shown that pop...

Ornamental traits function by improving attractiveness and are generally presumed to experience directional selection for mating success. However, given the greater investment of females in offspring than males, female-specific ornaments can in theory signal fecundity yet be constrained by fecundity costs. Theoretical work predicts that such constraints can lead to stabilizing selection via mal...

Recent investigations into the origins of symbolism indicate that personal ornaments in the form of perforated marine shell beads were used in the Near East, North Africa, and SubSaharan Africa at least 35 ka earlier than any personal ornaments in Europe. Together with instances of pigment use, engravings, and formal bone tools, personal ornaments are used to support an early emergence of behav...

The handicap principle suggests that individuals of superior quality can more easily bear the cost of developing extravagant ornaments. Consequently, ornament size should provide reliable information about quality or condition. Previous models have largely ignored the process of ornament growth, focusing only on final ornament size. We model ornament growth schedules for individuals of differen...