Encyclopedia of Evolution.pdf - Online Reading Center

Carl R. Woese pioneered the use of nucleotide sequence comparisons
to reconstruct evolutionary history of all organisms. (Courtesy of Bill
Wiegand/University of Illinois News Bureau)
was necessary to amplify the DNA of a particular gene, then
to separate it into fragments on a thin gel, a process called
electrophoresis. Radioactively labeled segments exposed a
sheet of photographic film, producing a barcode pattern that
allows the researcher to determine the sequence of nucleotides
in the DNA (see bioinformatics). Woese’s insight was
to choose a gene that all organisms possess: the gene for a
type of ribosomal RNA. Not only is this gene universal, but
it changes very slowly over evolutionary time. Woese worked
8–12 hours at a stretch, looking at the photographic sheets
in a darkroom, nearly every day for 10 years. The first gene
sequence took him nearly a year. Similar work can now be
done in a few days. By 1976 Woese had sequenced the ribosomal
RNA gene from 60 kinds of bacteria. Woese was also
one of the first scientists to analyze relationships among species
by producing a phylogenetic tree, a process used today in
the study of cladistics.
Then in 1976 a colleague suggested that Woese should
analyze a methanogenic bacterium. Methanogens (“methane
producers”) live in anaerobic swamp conditions. When
Woese completed the nucleotide sequence of this methanogen,
he found that it resembled none of the other prokaryotes.
Its ribosomal RNA was as different from those of the
other prokaryotes as from more complex organisms such as
plants and humans. Woese repeated his analysis to make sure
of his results. As he analyzed other prokaryotes that live in
conditions of extreme heat, acidity, and salinity, he found
that many of them clustered into a group separate from the
bacteria. He called this cluster archaebacteria (now called
Archaea). Based on ribosomal RNA sequences, Woese constructed
the first version of the now famous tree of life, which
classified all life-forms into three main branches: the archaebacteria,
the bacteria, and eukaryotes (see eukaryotes, evolution
of). This tree revealed that almost all of the genetic
diversity was found among microbes; the plants, animals, and
Wright, Sewall
fungi formed three tiny twigs of the tree of life. Two archaebacteria
that look similar to human observers might be as
different from one another, on the genetic level, as a mouse
and a spider. While this was at first surprising, in retrospect
it made sense. Almost 80 percent of the evolutionary history
of life occurred during Precambrian time, when most lifeforms
were microbial.
For the decade after Woese’s 1977 discovery of Archaea,
most microbiologists paid little attention to his work. One scientist
even cautioned the colleague who had given Woese the
methanogen to distance himself from Woese’s work. Major
new concepts in science often meet with considerable resistance
before being accepted (see scientific method). Woese
shared this experience with other evolutionary scientists who
proposed bold new concepts: punctuated equilibria (see
Gould, Stephen Jay; Eldredge, Niles), sociobiology
(see Wilson, Edward O.), and symbiogenesis (see Margulis,
Lynn). His work gradually moved from acceptance
to become the new standard view. By 2000 Woese had won
the top award in microbiology, and the National Medal of
Science, an award also won by Wilson and by Margulis. In
2003 Woese won the Crafoord Prize from the Royal Swedish
Academy of Sciences, the award given to scientists in areas of
research that are not covered by the Nobel Prize.
Woese has also contributed creative insights into the
origin of life and the origin of the genetic code (see DNA
[raw material of evolution]). Woese continues to do
research at the University of Illinois, focusing on the effects
that horizontal gene transfer may have had on the evolution
of the earliest life-forms.
Further Reading
Woese, Carl R. “Interpreting the universal phylogenetic tree.” Proceedings
of the National Academy of Sciences USA 97 (2000):
8,392–8,396.
———, and G. E. Fox. “Phylogenetic structure of the prokaryotic
domain: The primary kingdoms.” Proceedings of the National
Academy of Sciences USA 74 (1977): 5,088–5,090.
Wright, Sewall (1889–1988) American Evolutionary geneticist
Sewall Wright was an American geneticist who contributed
greatly to the understanding of population genetics and
evolution, principally by explaining the process of genetic drift
(see founder effect). He also has had a major and continuing
impact on many fields of scientific research, even more in
the social than in the natural sciences, by developing the statistical
method known as path analysis, a breakthrough method
that allowed correlations to be studied in complex systems. He
also made significant contributions to philosophy.
Born December 21, 1889, Wright grew up in Illinois
in an intellectual family. Very early in life, he showed great
mathematical ability and a passion for the natural world.
His father’s printing business published his pamphlet “The
Wonders of Nature” when Wright was seven years old. He
studied mathematics at Lombard College, where his father
taught. In graduate school at the University of Illinois and at
Harvard, Wright studied biology and genetics. He worked for