Then came the second surprise, announced by Woese and Fox in 1977, and now seen as one of the great paradigm shifts in biology. A deep divide emerged within the prokaryotic domain itself. A little-known group of prokaryotes, most of which inhabited extreme environments such as hot springs and hypersaline lakes, confounded all expectations when their ribosomal RNA was analysed. The analyses showed that they shared little more with the bacteria than the absence of a nucleus. As more of their ribosomal RNA was sequenced and compared, it became clear that the divergence was not just a new kingdom within the prokaryotes, but something much more basic-an entirely new domain, which has become known as the Archaea. Today, instead of five kingdom, we recognize three great domains of life : the Bacteria, the Archaea and the Eukaryotes. We ourselves , as animals, occupy no more than a small corner of the Eukaryotes.