[The basic outline of the evolution of single cell life-form].
In 1960s, kingdoms of organisms were charted generally in a five branching form. Later, the endosymbiont hypothesis for the mitochondria and the chloroplast was proposed. The life-form is divided into two forms, the prokaryotes (bacteria) and the eukaryotes. The study of the molecular biology made the progress faster. In 1980s, Woese, CR.asserted that two-domain view of life was no longer true, a three-domain construct, the Bacteria, the Archaea, and the Eukaryotes had to take its place. At first, phylogeny trees based on differences in the amino acid sequences, then among ribosomal RNAs and also nuclear gene from hundreds of microbial species were depicted and many mini phylogenetic trees grouped the species according to their differences in the sequences. It was found that they shared genes between their contemporaries and across the species barriers. At the root of the phylogeny tree, there was not a single common cell, it was replaced by a common ancestral community of primitive cells. Genes transfered rather freely as the transposons swapping between those cells. There was no last universal common ancestor of single cell that could be found in the revised Tree of Life, It was not easy to represent the genealogical patterns of thousands of different families of genes, in one systematic map, therefor there was no trunk at all.
Hu
Kai
K
Hainan University, The Tropical Biology Center, Haikou, Hainan, 570028, China. kaihu@public.hk.hi.cn
Wu
Qing-shu
QS