Natural populations are normally exposed to substantial environmental stress. In these circumstances, an association occurs between success in mating and extremes of sexual ornaments, rapid development, long life span, and low fluctuating morphological asymmetry. This association between important fitness traits depends on high metabolic efficiency underlain by genes for stress resistance and heterozygous advantage. In particular, the high energy demands from the development and maintenance of sexual ornaments imply that the "good genes" favored in the sexual selection process should be stress resistant. However, the generalized heterozygous advantage under stress suggests that many interacting genes are involved in promoting metabolic efficiency, so that the "good genes" approach should be replaced by a "good genotypes" approach. This "good genotype" approach has predictive power for incorporating additional fitness traits, especially where metabolic consequences can be perceived.