Phylogenetic System of Classification

Carl R Woese introduced a completely new approach in classification of organisms in 1977 that is based on evolutionary (phylogenetic) relationship among organisms. He meticulously analysed ribosomal ribonucleic acid (rRNA), genetic molecules that coordinate part of protein production. Because rRNA shows only slight variation from one generation to the next, it is an excellent tool for revealing the evolutionary, or family, relationships among organisms. Woese spent nearly a decade analysing the rRNA of various types of bacteria and arranging them into a microbial evolutionary tree. Use this concept all organisms are now classified into three kingdoms.
 They are
(1) Archaea,
(2) Bacteria, and
(3) Eukarya.