Five-Sixths of the history of life is the history of single-celled creatures only. (Gould)
Bacteria and Cyanophytes are prokaryotes, single cells whose genomes are diffuse. Prokaryotes are the most common form of life and arose before eukaryotes. A eukaryote cell contains organelles: a membrane-enclosed nucleus, which concentrates the genome, and mitochondria, which package the mechanisms for deriving energy by oxidation.
For the new bacteriology , bacteria are not so much single-celled individuals as a vast network of cells sharing a gene pool that may be compared to the data bank of of a large electronic communications network. (see Botkin, Discordant Harmonies, p. 114)
In the late 1960's Lynn (Sagan) Margulis proposed the Serial Endosymbiosis theory, proposing that eukaryotes are the results of symbiotic relationships within the cell. (The object of endocytobiology) According to this theory, the eukaryote cell is the result of the cooperative union of two or three prokaryotes. One of these became the nucleus, another became the energy generators (the mitochondria), and in plants the third type of cell became the cholorplasts.
Some implications of this view(see symbiosis) are than the "individuals" handled as unities in population equations are themselves symbiotic complexes involving uncounted numbers of live entities integrated in diverse ways in an unstudied fashion. This also means that "family trees" (phylogenies) would not only bifurcate, because the branches would have more than one ancestor. (see opposition of rhizome and tree) "Symbiogenesis" threatens orthodox neo-Darwinism, with its fixation on random mutation and selection as the sole sources of evolution. (and competiton as opposed to cooperation).
Symbioticists claim that some of the resistance of Darwinists to their theories is because "Mutualism", parasitism, and other terms of symbiosis have carried associated meanings well beyond their biological scope. They believe that scientific discussions regarding the relative roles of "competition" and "cooperation" are influenced by cultural associations.
(Histories of the origins of life must deal with the emergence of the eukaryote...see Lynn Margulies and Dorion Sagan, Microcosmos, which describes the dynamics of microbial ecosystems as the foundation of all living systems on this planet.) The realization of the significance of microbial ecosystems for the health of our planet was a major component in the elaboration of the Gaia hypothesis by James Lovelock and Lynn Margulis.