genetic mutations update

[Guest guest]

Not only has life evolved, but life has evolved to evolve

Published: Wednesday, 11-Aug-2004 News-Medical.Net

That's the conclusion drawn by two Rice University scientists who have

designed a computer simulation to test the idea that evolvability — the

likelihood of genetic mutation — is a trait that can itself be favored

or disfavored through the process of natural selection.

The results of the study appear in the Aug. 10 issue of Proceedings of

the National Academy of Sciences.

Researchers Deem, the W. Professor of Bioengineering

and professor of physics and astronomy, and Earl, Deem's

post-doctoral research fellow, drew their conclusions from a

sophisticated computer simulation that recorded how much and how rapidly

proteins mutated based on external changes in their environment. As the

researchers ramped up the frequency and severity of environmental

changes — imagine rapid shifts between heat waves and cold snaps or

heavy rains and droughts — they saw an increased likelihood of survival

among proteins that mutated more frequently.

“Selection for evolvability would help explain a growing body of

experimental results including the evolution of drug resistance in

bacteria, the fact that some immune system cells mutate much more

rapidly than other cells in our bodies, as well as why some bacteria and

higher-order organisms have a tendency to transpose or swap relatively

long sequences of DNA,” said Deem.

Traditionally, a significant number of evolutionary biologists have

discounted the idea that evolvability is subject to natural selection,

in part because the idea that evolution acts upon the mechanism that

causes evolution seems to violate the basic scientific principle that an

event cannot precede its own cause.

But Deem and Earl argue that causal violations need not occur. For one

thing, there are several different ways that genetic mutations occur.

Random changes along the DNA chain are now understood to be only one way

that organisms evolve. Mutations also occur based on genetic

recombination, genetic transposition and horizontal gene transfer. With

these mechanisms, relatively large chunks of genetic code are shuffled

or substituted for one another along the DNA chain.

Deem and Earl's argument centers on the idea that the ability to reorder

genes or to cause large-scale genetic change are themselves genetic

traits, traits that are subject to selection like any others.

The upshot of this is that many observations within evolutionary biology

that were heretofore considered evolutionary happenstance or accidents,

may in fact be explained by selection for evolvability.

Two primary examples of this can be found in the escalating “arms race”

that has been documented between pathogens and the immune systems in

people and other higher-order vertebrates. Deem and Earl argue that wide

variation among bacteria and other antigens has put selective pressure

on our immune systems to rapidly adapt methods of identifying and

attacking invaders. Similar observations on the rapid mutability among

flu viruses and other invading pathogens provide additional evidence,

they said.

“The implication is that the drugs we have developed to fight invading

pathogens also confer selective pressure on the evolvability of the

pathogens themselves,” Earl said. “In drug design, it is important to

consider this and to look for ways to minimize or counteract this

driving force for drug resistence.”

http://www.rice.edu