Scientific News  Biology Biotechnologies DIGITAL ORGANISMS USED TO CONFIRM EVOLUTIONARY PROCESS
DIGITAL
ORGANISMS USED TO CONFIRM EVOLUTIONARY PROCESS
 Using
a revolutionary computer program that gives scientists the opportunity to watch
evolution take place before their eyes
using "digital organisms," a team of researchers from Michigan
State University and Caltech has confirmed an evolutionary process long
suspected but, until now, unproven.
In a paper published in the July 19
edition of the journal 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's title: "Evolution
of Digital Organisms at High Mutation Rates Leads to Survival of the Flattest."
This play on Darwin's own "survival of the fittest" incorporates 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 colleagues make the
analogy to mountain climbing: 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."
Specifically, the researchers found
that there is tradeoff between producing offspring faster and making them better
able to withstand the harmful effects of most mutations. The bottom line: 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 that creates
the digital organisms used to do this work is called "Avida" - A for
artificial and vida is Spanish for life. It gives scientists the chance 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 comparable 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."
Teaming with Lenski and Ofria on
this paper were Christoph Adami of the Jet Propulsion Laboratory, Caltech; and
Claus Wilke and Jialan Wang of Caltech's Digital Life Laboratory.
The National Science Foundation
funded the work.
Contact:
Source
of the given news and the copyrights belong to a Michigan
State University
Publishing date: August 15, 2001
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