Carl Woese Papers, 1911-2013 | University of Illinois Archives

Carl Woese (1928-2012), who revolutionized the science of microbiology, has been called the Darwin of the 20th century. Darwin's theory of evolution dealt with multicellular organisms; Woese brought the single-celled bacteria into the evolutionary fold. The Syracuse-born Woese began his early career as a newly minted Yale Ph.D. studying viruses but he soon joined in the global effort to crack the genetic code. His 1967 book The Genetic Code: The Molecular Basis for Genetic Expression became a standard in the field. Woese hoped to discover the evolutionary relationships of microorganisms, and he believed that an RNA molecule located within the ribosoma, the cell's protein factory offered him a way to get at these connections.

A few years after becoming a professor of microbiology at the University of Illinois in 1964, Woese launched an ambitious sequencing program that would ultimately catalog partial ribosomal RNA sequences of hundreds of microorganisms. Woese's work showed that bacteria evolve, and his perfected RNA fingerprinting technique provided the first definitive means of classifying bacteria. In 1976, in the course of this painstaking cataloging effort, Woese came across a ribosomal RNA fingerprint from a strange methane-producing organism that did not look like the bacterial sequences he knew so well. As it turned out, Woese had discovered a third form of life, a form of life distinct from the bacteria and from the eukaryotes (organisms, like humans, whose cells have nuclei); he christened these creatures the archaebacteria only to later rename them the archaea to better differentiate them from the bacteria.

In 1980, four years after his discovery of the archaea, Woese unveiled the Big Tree, the first tree of life based entirely on ribosomal RNA data. Woese's tree attempted to trace the evolutionary relationships of the three forms of life going back to their divergence from a common ancestor over three billion years ago. Continuing to probe the origins of life for the rest of his career, Woese would help develop such seminal concepts as the RNA World and the progenote. a hypothetical communal state of life predating the first cell. In 1990 Woese proposed that all life be grouped into three domains: the Archaea, the Bacteria, and the Eucarya. This idea met a great deal of resistance from many of his fellow biologists but is now largely enshrined in the textbooks. Carl Woese died on December 30, 2012, in Urbana, Illinois.