By that measure (number of organisms) prokaryotes are the future. https://en.wikipedia.org/wiki/Lists_of_organisms_by_population#By_domain https://en.wikipedia

By that measure (number of organisms) prokaryotes are the future. https://en.wikipedia.org/wiki/Lists_of_organisms_by_population#By_domain https://en.wikipedia.org/wiki/Lists_of_organisms_by_populati... (as to birthrates, cursory googling suggests they have birthrates from on the order of 10e30 individuals per year to on the order of 10e30 individuals per week)