Jan 29, 2007 (PhysOrg.com) – 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.

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.”

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Make no mistake, this is where evolutionary theory is headed. Not that HGT makes any more sense than point mutations, but the constant appeals to parallel evolution have gotten to the point where no one could honestly take them seriously.