= Carl R. Woese
{c}
<Carl R. Woese> (1928–2012) was a <microbiologist> who used <ribosomal RNA> comparisons to investigate deep evolutionary relationships. His work with <George E. Fox> helped establish that <Archaea> form a major lineage distinct from <bacteria>, despite both groups lacking a cell nucleus.<Carl R. Woese memorial at the University of Illinois>[December 31, 2012, molecular classification and discovery of Archaea]{ref}
Their 1977 paper inferred three primary lines of descent from <ribosomal RNA> sequence characterization.<Phylogenetic structure of the prokaryotic domain: the primary kingdoms by Carl R. Woese and George E. Fox>[Abstract, three proposed groups]{ref} The related experimental work compared catalogs of short fragments obtained from <16S ribosomal RNA> by <ribonuclease T1> digestion.<Classification of methanogenic bacteria by 16S ribosomal RNA characterization by George E. Fox and others>[Abstract, oligonucleotide characterization of ten methanogenic species]{ref} These were measurements of particular molecular sequences, rather than a classification based solely on visible cell shape.
A toy <phylogenetics> problem illustrates the motivation. Three rod-shaped microbes look alike, but a set of comparable molecular characters groups the first two together and separates the third. Cell shape alone would conceal that distinction. A molecular comparison can supply different evidence about shared ancestry, although interpreting it still requires an appropriate evolutionary model and enough informative characters.
The biological surprise was that methane-producing microbes could resemble ordinary <bacteria> at the level of broad cell organization while differing profoundly in the molecular evidence. Woese's approach made <ribosomal RNA> a way to test classifications of organisms whose appearance supplied few distinctive clues.<Carl R. Woese memorial at the University of Illinois>[Research account, ribosome comparisons and methane-producing microbes]{ref}
The historical proposal is a foundation for the <three-domain system>. It does not settle every later question about the root and branching of the <phylogenetic tree>; the <two-domain system> addresses a different arrangement of the deepest relationships. Woese's enduring methodological contribution was to make such questions answerable through explicit molecular comparisons.
\Image[https://media.news.illinois.edu/wp-content/uploads/2024/12/19145714/40324.jpg]
{title=Carl R. Woese}
{description=Portrait by Jason Lindsey, identified by the University of Illinois memorial: https://news.illinois.edu/carl-r-woese-who-discovered-a-new-domain-of-life-dies-at-84/ .}
{height=300}
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