The Tree of Life
The Tree of Life
Universal Phylogeny and Its Discontents
The idea that all living things arose from their progenitors by descent with modification, and that this history can be depicted as a great tree, goes back to Darwin and beyond. Construction of a universal tree became possible after Carl Woese introduced ribosomal RNA sequences as a molecular chronometer. The tree consists of three great stems, or domains, designated Bacteria, Archaea and Eukarya, and this tripartite division is now generally accepted. But soon a serious complication arose: lateral transfer of genes between species, genera and even domains is common, particularly among prokaryotes. Lateral gene transfer erodes the phylogenetic trace, and has led some to question the very principle of a tree of life, but the division of all living things into three domains has held up. It is not easy to assign absolute dates to their emergence. The prokaryotes, Bacteria and Archaea, clearly go back more than 3 billion years. Modern Eukarya are much more recent, a billion years or so, but the eukaryotic lineage appears to be very ancient, possibly comparable to the prokaryotic ones.
Keywords: tree of life, ribosomal RNA, three domains, lateral gene transfer, molecular phylogeny, dating the divergences, Carl Woese
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