 Barker goes further and suggests what might unify the different lineages that fall under different species concepts. Baker argues that the pluralists’ focus on the different forces that cause species lineages (interbreeding, ecological, and phylogenetic) is the wrong place to look for unity in the species category. Instead, he suggests we should look for the common effect of species lineages. The common effect he focuses on is species cohesiveness. He suggests that species lineages are metapopulational feedback systems. Such systems have cohesifying processes that cause further cohesifying processes. Barker cites the example of selection for a particular flower color in a South American plant species. That color is very attractive to pollinators, thus causing pollinators to more frequently visit that species’ flowers. That, in turn, causes the genes of the plant to be more widely spread to other populations of that species. In this example, selection causes the enhancement of another cohesifying force, gene flow, among the members of a species. As Barker recognizes, his suggestion concerning feedback and cohesiveness in species is a theoretical hypothesis that needs empirical confirmation. Nevertheless, it provides a new way that species monists may secure their position.