Expansionary Institute

Michael Zey
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Science NewsTM
Digital Organisms Used to Confirm Evolutionary Process
July 19, 2001 7:30 CDT
Scientists from Michigan State University and Caltech
are using a revolutionary computer program that gives
them the opportunity to watch evolution happen right
before their eyes through "digital organisms." The
researchers have confirmed an evolutionary process long
suspected but unproven until now. In a paper published
in the July 19th edition of Nature, MSU researchers
Richard Lenski and Charles Ofria, along with colleagues
at Caltech, provided some insight into one aspect of
Darwin's theory of natural selection that they dubbed
"survival of the flattest."

The paper is titled "Evolution of Digital Organisms at
High Mutation Rates Leads to Survival of the Flattest."
This play on Darwin's "survival of the fittest" combines
the fact that fitness depends not only on the quantity
of offspring an organism can produce in its lifetime,
but also how fit those offspring will be.

Lenski and his colleagues use a mountain climbing
analogy: the height of the peak you are on is your speed
of replication, and the strength of the winds your
mutation rate. If there were only a gentle breeze, you
would be most fit by climbing to the highest peak you
can. But in a more turbulent hurricane, you would want
to find someplace where there is not such a long
distance to fall - someplace flat.

A fast replicator may be producing many children, but if
it's too susceptible to the harmful effects of
mutations, it won't contribute to future generations
much beyond that. As Lenski put it, "It would have lots
of children but not lots of grandchildren." The
researchers specifically found a tradeoff between
producing offspring faster and making them better able
to stand the harmful effects of most mutations.

The bottom line is this: When mutation rates are high,
it is better for a species to reproduce more slowly if
this allows its offspring to avoid being seriously
harmed by mutations. "Theory predicts that genomes that
have evolved at a high mutation rate will have become
more robust to the harmful effects of mutations than
genomes that have evolved at a low mutation rate," said
Lenski, MSU Hannah Professor of Microbial Ecology.

"However, theory also predicts that there is a price to
be paid for this robustness, which is that more robust
genomes will tend to replicate more slowly than genomes
that are less robust."

"A species that can reproduce quickly, but loses most of
its offspring due to frequent, deleterious mutations may
be out-competed by a slower, but more robust species,"
said Ofria, assistant professor in MSU's Center for
Microbial Ecology. The computer software used in the
study is called "Avida" - A for artificial and vida is
Spanish for life. It allows scientists to watch over a
period of a few hours a natural evolutionary process
that would normally take years. "Using Avida, the
digital organisms can mutate at a rate that we can
control in our experiments," Lenski said. "Hence, we let
some populations evolve at low and others at high
mutation rates and examine the effects on growth and
susceptibility to mutation."

The digital organisms are similar to computer viruses,
"except digital organisms are harmless because their
programs are meaningless outside the special operating
environment in Avida," he said. The researchers do not
put any outside constraints on the computational
abilities of these programs. "Theoretically, any
possible algorithm can evolve," said Ofria, the creator
of the Avida system. "In fact, in each experiment, the
population proceeds along a new evolutionary pathway."

Source: Nature
Cosmiverse Staff Writer


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