Evolutionary Jump Starts

[David Morris]

http://physorg.com/news89292896.html

It's a mystery why the speed and complexity of evolution appear to
increase with time. For example, the fossil record indicates that
single-celled life first appeared about 3.5 billion years ago, and it
then took about 2.5 billion more years for multi-cellular life to
evolve. That leaves just a billion years or so for the evolution of
the diverse menagerie of plants, mammals, insects, birds and other
species that populate the earth.

New studies by Rice University scientists suggest a possible answer;
the speed of evolution has increased over time because bacteria and
viruses constantly exchange transposable chunks of DNA between
species, thus making it possible for life forms to evolve faster than
they would if they relied only on sexual selection or random genetic
mutations.

"We have developed the first exact solution of a mathematical model of
evolution that accounts for this cross-species genetic exchange," said
Michael Deem, the John W. Cox Professor in Biochemical and Genetic
Engineering and professor of physics and astronomy.

The research appears in the Jan. 29 issue of Physical Review Letters.

Past mathematical models of evolution have focused largely on how
populations respond to point mutations – random changes in single
nucleotides on the DNA chain, or genome. A few theories have focused
on recombination – the process that occurs in sexual selection when
the genetic sequences of parents are recombined.

Horizontal gene transfer (HGT) is a cross-species form of genetic
transfer. It occurs when the DNA from one species is introduced into
another. The idea was ridiculed when first proposed more than 50 years
ago, but the advent of drug-resistant bacteria and subsequent
discoveries, including the identification of a specialized protein
that bacteria use to swap genes, has led to wide acceptance in recent
years.

"We know that the majority of the DNA in the genomes of some animal
and plant species – including humans, mice, wheat and corn – came from
HGT insertions," Deem said. "For example, we can trace the development
of the adaptive immune system in humans and other jointed vertebrates
to an HGT insertion about 400 million years ago."

"Life clearly evolved to store genetic information in a modular form,
and to accept useful modules of genetic information from other
species," Deem said.