Well, you'll have to explain to me how a detailed analysis of the kai genes across a large number of species of cyanobacteria, proteobacteria, and archaei, showing that their interrelationships have the form of a tree, and how that tree has a very similar structure to the tree obtained by examining relationships between the genes for a completely different molecule, the 16S RNA, is a 'just-so' story.
To help you, here are the two trees. Enjoy. 