ABSTRACT
C. R. Woese regarded the urkaryotes as the non-nucleated and non-bacterial ancestors of the eukaryotic cytoplasm, in other words as akaryotes, very much as Roger Stanier did. Urkaryotes, archaebacteria and eubacteria originated therefore independently from a common ancestor very early in the history of life, and have evolved along separate lines of descent ever since. They were the three primary kingdoms of cellular evolution. The origin of natural and profound discontinuity will become the third entry in our list of unsolved mysteries in cellular evolution. According to Stanier, the ancestors of the eukaryotes were non-nucleated cells like prokaryotes, but biochemically and phylogenetically they had nothing to do with bacteria and cannot therefore be regarded as prokaryotes. In 1970 Stanier pointed out that the microorganisms which engulfed prokaryotes by endosymbiosis could not have been prokaryotes themselves because the impenetrability of the prokaryotic cytoplasmic membrane by any object of supramolecular dimensions effectively precludes the acquisition of endosymbiosis.
