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Resources are often central to the formation and persistence of human consortships, and to the evolutionary fitness consequences of those consortships. As a result, the distribution of resources within a society should influence the number and quality of mating opportunities an individual of given status/wealth experiences. In particular, in a wide variety of societies, both contemporary and historic, women have been shown to prefer mates of higher rather than lower status and wealth, a pattern known as ‘hypergyny’. Such status-dependent within-sex competition is likely to be influenced not only by the preferences individuals express but also by the distribution of resources within and between sexes. Empirical studies show that economic inequality within a sex can amplify mating competition, and that inequalities between women and men also influence behaviours related to mating competition, but the links between resource distribution and mating competition have attracted limited systematic attention. We present simulation models of hypergynous preferences and the effects on mating competition among men and among women within a heterosexual mating market. Our modelling shows that the lower mating success of poorer men and richer women (when compared with richer men and poorer women) is worsened when resource gender gaps are relatively small or when women out-earn men on average. Likewise, high economic inequality, especially among men, amplifies the competition experienced by these groups. We consider the political implications in terms of sex- and status-dependent attitudes to gender equity, income inequality, and hypergynous mating norms.

Costly signalling theory is based on the idea that individuals may signal their quality to potential mates and that the signal's costliness plays a crucial role in maintaining information content (‘honesty’) over evolutionary time. Whereas costly signals have traditionally been described as ‘handicaps’, here we present mathematical results that motivate an alternative interpretation. We show that under broad conditions, the multiplicative nature of fitness selects for roughly balanced investments in mating success and viability, thereby generating a positive correlation between signal size and quality. This balancing tendency occurs because selection for increased investment in a fitness component diminishes with the absolute level of investment in that component, such that excessively biased investments are penalised. The resulting interpretation of costly signals as balanced (albeit not necessarily equal) investments may be a widely applicable alternative to the traditional ‘handicap’ metaphor, which has been criticised for its non-Darwinian connotation of selection for ‘waste’ rather than efficiency. We predict that accelerating returns on viability are necessary to undermine honesty. This prediction depends crucially on the assumption that mating success and viability contribute multiplicatively (rather than additively) to an individual's fitness. peerReviewed

A fundamental task of evolutionary biology is to explain the pervasive impression of organismal design in nature, including traits benefiting kin. Inclusive fitness is considered by many to be a crucial piece in this puzzle, despite ongoing discussion about its scope and limitations. Here we use individual‐based simulations to study what quantity (if any) individual organisms become adapted to maximise when genetic architectures are more or less suitable for the presumed main driver of biological adaptation: namely, cumulative multi‐locus evolution. As an expository device we focus on a hypothetical situation called Charlesworth’s paradox, in which altruism is seemingly predicted to evolve, yet altruists immediately perish along with their altruistic genes. Our results support a recently proposed re‐definition of inclusive fitness, which is concerned with the adaptive design of whole organisms as shaped by multi‐locus evolution, rather than with selection for any focal gene. They also illustrate how our conceptual understanding of adaptation at the phenotypic level should inform our choice of genetic assumptions in abstract simplified models. peerReviewed

The evolution of dispersal tendencies and of cognitive abilities have both been intensely studied. Yet little attention has been given to the question of how these two aspects may relate to each other, as a result of their joint evolution. On the one hand, learning abilities may help dispersers to cope with their new habitat. On the other hand, dispersal may sometimes reduce the need for learning, because local environments may differ in how much there is to learn. To get a better understanding of this relationship, we built an individual‐based simulation in which both learning speed and dispersal tendency were free to evolve. We found that both positive and negative correlations could evolve between these traits, depending on properties both of local patches and of the metapopulation as a whole. We also found that dispersal stabilized the co‐existence of different cognitive types in the metapopulation, underscoring its importance for maintaining biodiversity within species. peerReviewed

Sex allocation theory predicts that the proportion of daughters to sons will evolve in response to ecological conditions that determine the costs and benefits of producing each sex. All else being equal, the adult sex ratio (ASR) should also vary with ecological conditions. Many studies of subterranean species reported female-biased ASR, but no systematic study has yet been conducted. We test the hypothesis that the ASR becomes more female-biased with increased isolation from the surface. We compiled a dataset of ASRs of 35 species in the subterranean amphipod Niphargus, each living in one of three distinct habitats (surface-subterranean boundary, cave streams, phreatic lakes) representing an environmental gradient of increased isolation underground. The ASR was female-biased in 27 of 35 species; the bias was statistically significant in 12 species. We found significant difference in the ASR among habitats after correction for phylogeny. It is most weakly female-biased at the surface-subterranean boundary and most strongly female-biased in phreatic lakes. Additional modelling suggests that the ASR has evolved towards a single value for both surface-subterranean boundary and cave stream dwelling species, and another value for 9 of 11 phreatic lake dwellers. We suggest that a history of inbreeding in subterranean populations might lower inbreeding depression such that kin selection favours mating with siblings. This could select for a female-biased offspring sex ratio due to local mate competition among brothers. The observed patterns in sex ratios in subterranean species make them a group worthy of more attention from those interested in sex allocation theory. peerReviewed