Many organisms increase their population through sexual reproduction. For sexual reproduction success, individuals of the same species with different mating types must recognise each other accurately. Recently, it has been reported that the eukaryotic fission yeast Schizosaccharomyces pombe possesses a bidirectional ligand-receptor recognition system in which one side is stringent and another is loose. Interestingly, this asymmetric recognition system has also been observed in other species, some of which have the roles reversed. This system has been discussed as a potential contributor to diversification in sympatric speciation. However, the origin of this system remains unclear. When investigating this, we found that this system spontaneously emerges from a population genetics-based mathematical model that assumes external environmental fluctuations and population-dependent effects. This suggests the existence of a universal rule governing the formation of such an asymmetric recognition system in sexual reproduction.