Two-empire system

It classified cellular life into Prokaryota and Eukaryota as either "empires" or "superkingdoms".

However, given the current state of knowledge and the rapid progress in biological scientific advancement, especially due to genetic analyses, that view has all but vanished.

Some prominent scientists, such as the late Thomas Cavalier-Smith, still hold and held to the two-empire system.

[1] The late Ernst Mayr, one of the 20th century's leading evolutionary biologists, wrote dismissively of the three-domain system, "I cannot see any merit at all in a three empire cladification.

"[2] Additionally, the scientist Radhey Gupta argues for a return to the two-empire system, claiming that the primary division within prokaryotes should be among those surrounded by a single membrane (monoderm), including gram-positive bacteria and archaebacteria, and those with an inner and outer cell membrane (diderm), including gram-negative bacteria.