Koinophilia replaces random mating in populations subject to mutations with randomly varying fitnesses.

Koinophilia, the avoidance of sexual mates bearing strange phenotypic features, or displaying odd behaviour, would, if it evolved, profoundly influence the evolutionary process. A stochastic computer model was therefore devised to investigate the evolution of an initially rare koinophilic trait in panmictic populations, subject to mutations with randomly varying fitnesses. Individual genomes consisted of 50 genes. Mutations occurred at a rate of 0.005, 0.01 or 0.02 per gene per generation. The mean and maximum fitness of mutations could be varied, as could the proportion of beneficial mutations. The carriers of the koinophilic trait avoided, with adjustable degrees of intensity, mates displaying unusual phenotypic features (traits with population frequencies < 0.5); panmictic individuals mated randomly. The results show that koinophilia tends to replace panmixis whenever the preference for common phenotypic traits is strongly expressed, when few mutations are beneficial (1% instead of 10%), or when the maximum fitness of mutations is low (1.2 instead of 2.0). The mutation rate and mean fitness of mutations had only minor effects on the relative advantage of koinophilia.