Local mating markets in humans and non-human animals

Abstract

In biology, the term ‘mating market’ has been fashionable for a few decades only, but sexual selection theory was implicitly based on economic principles from the start. I regard mating individuals explicitly as traders on markets and distinguish ‘global mating markets’, consisting of all reproducing members of a population, from ‘local mating markets’ (LMMs) that are disconnected in space and/or time. I focus on ways in which individuals make the best of variation among LMMs by adapting their mating strategy to each local market they enter. The ‘operational sex ratio’ (OSR; Emlen ST, Oring LW (1977) Science 197:215–223) gives a first approximation of the balance of power between the two trader classes: males and females ready to reproduce. The parameter I use is the local OSR (LOSR), the OSR of a single LMM. The balance of power is dependent not only on the LOSR, however, but also on the production costs and exchange values of ‘crucial commodities’, which often vary locally and over time. Distinguishing LMMs is most useful for species with strong variation in the LOSR. Human mating markets distorted by war, selective abortion and sex-biased migration are among the best-documented local markets with aberrant OSRs. Traders on LMMs may strategically adjust to supply and demand ratios and changes in their own market value but also attempt to change local market conditions or transfer to another local market with better conditions. Fine-tuning can result not only from conditional strategies, evolved under natural and sexual selection, but also from learning processes as far as species-specific cognitive constraints allow. Biological market theory (BMT), which deals with cooperation among unrelated agents in general, is combined with sexual selection theory (SST), which deals with reproductive cooperation, to focus on an aspect that received little attention in the vast SST literature: adaptations that improve mating success when the market value of an individual varies considerably from one local mating market (LMM) to the next. An individual’s market value on an LMM is determined not only by the local operational sex ratio (LOSR) but also by the value of the goods and services that both sexes invest in their mates and/or the communal offspring. Case studies of both humans and non-human animals are used to illustrate the difference between global and local markets and to evaluate predictions based on the LMM-hypothesis.