Simpson and Grant. That most inclusive population of individual biparental organisms which share common fertilization system'. Species kept distinct by common fertilization system. Mechanistic basis for unity of species. Applies only to bisexual eukaryotes.
Loudspeakers play songs of different species from either side.
The most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms'. Balance between genetic and demographic exchangeability. Applicability to all types of species and modes of reproduction. Complex program of research required to understand cohesion mechanisms. Based on process.