Across the animal kingdom, striking displays and ornaments are produced by sexual selection. Current thinking is that females choose the most elaborate males because they display genetic benefits to offspring. However, this should lead to a rapid decline in genetic variation within species. Variation between individuals is the raw material upon which selection acts, so how is this variation maintained? Solving this ‘paradox of the lek’ continues to be one of the most contentious issues in evolutionary ecology.This proposal suggests that three important factors have been overlooked in the study of sexual selection. First, individual differences in mate preference function for direct verses indirect benefits are expected to vary with the choosers own phenotype, and thus serve to maintain variation within populations. Second, mutual mate choice has been neglected, and sex specific optima are expected to play a key role. Third, non-genetic parental effects are closely linked with mate preference and have huge implications for selection, but such effects are rarely considered in this context.I propose to test how these factors influence variation using an established population of wild great tits, which are amenable to carefully controlled lab and field experiments. I will complement phenotypic studies with state-of-the-art SNP genotyping and modeling techniques to determine how the heritability of shared traits and preference functions, and selection for heterozygosity affect genetic variation. This uniquely integrative approach will answer a fundamental question in evolutionary biology: How is genetic variation maintained by sexual selection? The answer to this question is key to our understanding of evolutionary processes, the likelihood of extinction and speciation, as well as animal breeding.