Does evolution select for faster evolvers?

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."

The new mathematical model developed by Deem and visiting professor Jeong-Man Park attempts to find out how HGT changes the overall dynamics of evolution. In comparison to existing models that account for only point mutations or sexual recombination, Deem and Park's model shows how HGT increases the rate of evolution by propagating favorable mutations across populations.

Deem described the importance of horizontal gene transfer in the work in a January 2007 cover story in the Physics Today, showing how HGT compliments the modular nature of genetic information, making it feasible to swap whole sets of genetic code – like the genes that allow bacteria to defeat antibiotics.

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

Source: Rice University

Related stories:

Changing environment organizes genetic structure
What is the fundamental creative force behind life on Earth? It's a question that has vexed mankind for millennia, and thanks to theory and almost a year's worth of number-crunching on a supercomputer, Rice University physicist and bioengineer Michael Deem thinks he has the answer: A changing environment may organize the structure of genetic information itself.
Thumbs up -- a tiny ancestral remnant lends developmental edge to humans
Subtle genetic changes that confer an evolutionary advantage upon a species, such as the dexterity characteristic of the human hand, while difficult to detect and even harder to reproduce in a model system, have nevertheless generated keen interest amongst evolutionary biologists. In findings published online in the September 5 edition of the journal Science, researchers from the U.S. Department of Energy's Lawrence Berkeley National Laboratory and their collaborators, have uncovered a specifically human 13-nucelotide change concealed in the vast three-billion-letter landscape of the human genome.
Gene enhancer in evolution of human opposable thumb
Scientists have discovered a gene enhancer, known as HACNS1, that may have contributed to the evolution of the uniquely opposable human thumb, and possibly also modifications in the ankle or foot that allow humans to walk on two legs, according to a paper published in Science on Sept. 5, 2008.
Researchers Find 'Junk DNA' May Have Triggered Key Evolutionary Changes in Human Thumb and Foot
(PhysOrg.com) -- Out of the 3 billion genetic letters that spell out the human genome, Yale scientists have found a handful that may have contributed to the evolutionary changes in human limbs that enabled us to manipulate tools and walk upright.
DNA shows that last woolly mammoths had North American roots
In a surprising reversal of conventional wisdom, a DNA-based study has revealed that the last of the woolly mammoths—which lived between 40,000 and 4,000 years ago—had roots that were exclusively North American.
Molecular evolution is echoed in bat ears
Echolocation may have evolved more than once in bats, according to new research from the University of Bristol published this week in Proceedings of the National Academy of Sciences (PNAS).
New research challenges long-held assumptions of flightless bird evolution
Large flightless birds of the southern continents – African ostriches, Australian emus and cassowaries, South American rheas and the New Zealand kiwi – do not share a common flightless ancestor as once believed.
Cell division study resolves 50-year-old-debate, may aid cancer research
A new study at Oregon State University has finally resolved a controversy that cellular biologists have been arguing over for nearly 50 years, with findings that may aid research on everything from birth defects and genetic diseases to the most classic "cell division" issue of them all – cancer.

News discussion:

So much for GMO Luddism in Physics news