- Forget what you learned in biology about the origin of
life: that it began with a single mother of all cells and became increasingly
complex. It was a simplistic notion anyway.
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- A new theory by leading evolutionary microbiologist Carl
Woese, which may revolutionize notions on the origin of life, suggests
that life really began with at least three primitive cell-like structures
engaged in a promiscuous gene-swapping free-for-all more than 3 billion
years ago. At different points in time, these genetic swingers settled
down and only then gave rise to the three known branches of the tree of
life " bacteria, eukaryotes (like the cells in our bodies) and archaea
(such as the organisms that thrive around deep-sea vents). Woese's theory
is described for the first time in today's Proceedings of the National
Academy of Science.
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- As it is explained currently, comets seeded the earth
with organic chemicals, then something unknown happened and cells appeared
that gave rise to increasingly complex organisms in that Darwinian "Origin
of Species" way.
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- Woese, of the University of Illinois at Urbana-Champaign,
does not dispute Darwin's theory for those first cells. But Woese says
that an even earlier form of evolution took place during that unknown period
under a completely different set of rules.
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- For the past 100 years, evolution has been viewed as
a vertical process with genes flowing from one organism to the next with
genetic variations occurring along the way. This was not unlike family
trees with an ancestor at the top and genetic descendents, all a little
different from their parents, flowing downward.
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- Woese proposes a form of horizontal evolution in which
genes are passed around more like soccer balls from one player to the next
without causing any significant changes in the basic structure of the pre-cellular
organisms. Theoretically, 10% of the organism's genes are its own and 90%
are interchangeable. This passing back and forth of genes is called horizontal
gene transfer.
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- The idea of horizontal gene transfer has been around
for decades, but it was considered a rare event in terms of influencing
evolution. But Woese says horizontal gene transfer was the initial driving
force of evolution that led life from the organic chemical muck to bacteria,
eukaryotes and archaea upon which Darwin's evolution has done its more
elaborate work. He developed the theory by studying the genetic codes,
or sequences, of different types of cells.
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- Woese revolutionized biology once before in the late
1970s with the theory that life has three main branches. Before Woese,
scientists had taught that only two branches existed. Most scientists accepted
Woese's theory, and in 1996, he put to rest any lingering doubts by comparing
the genetic codes of bacteria, eukaryotes and archaea.
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- Genetic codes are a powerful new source of information
about evolution. Differences and similarities in genetic codes can reveal
how closely organisms may be related and how far back in time they split
into different types.
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- Leading biologists say Woese's new theory promises to
fill in the gap in scientific thinking about the origin of life.
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- "I think the most important point," says Norman
Pace, of the University of Colorado, Denver, "is that it explains
what happened in the black box between the appearance of organic chemicals
and Darwinian evolution."
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