Sunday, January 31, 2010

Horizontal and vertical: The evolution of evolution - life - 26 January 2010 - New Scientist

A look at how evolution itself may have evolved. Horizontal and vertical: The evolution of evolution - life - 26 January 2010 - New Scientist

JUST suppose that Darwin's ideas were only a part of the story of evolution. Suppose that a process he never wrote about, and never even imagined, has been controlling the evolution of life throughout most of the Earth's history. It may sound preposterous, but this is exactly what microbiologist Carl Woese and physicist Nigel Goldenfeld, both at the University of Illinois at Urbana-Champaign, believe. Darwin's explanation of evolution, they argue, even in its sophisticated modern form, applies only to a recent phase of life on Earth.

At the root of this idea is overwhelming recent evidence for horizontal gene transfer - in which organisms acquire genetic material "horizontally" from other organisms around them, rather than vertically from their parents or ancestors. The donor organisms may not even be the same species. This mechanism is already known to play a huge role in the evolution of microbial genomes, but its consequences have hardly been explored. According to Woese and Goldenfeld, they are profound, and horizontal gene transfer alters the evolutionary process itself. Since micro-organisms represented most of life on Earth for most of the time that life has existed - billions of years, in fact - the most ancient and prevalent form of evolution probably wasn't Darwinian at all, Woese and Goldenfeld say.
In particular, he argues, nothing in the modern synthesis explains the most fundamental steps in early life: how evolution could have produced the genetic code and the basic genetic machinery used by all organisms, especially the enzymes and structures involved in translating genetic information into proteins. Most biologists, following Francis Crick, simply supposed that these were uninformative "accidents of history". That was a big mistake, says Woese, who has made his academic reputation proving the point.
This is all very different from evolution as described by Darwin. Evolution will always be about change as a result of some organisms being more successful at surviving than others. In the Darwinian model, evolutionary change occurs because individuals with genes associated with successful traits are more likely to pass these on to the next generation. In horizontal gene transfer, by contrast, change is not a function of the individual or of changes from generation to generation, but of all the microbes able to share genetic material. Evolution takes place within a complex, dynamic system of many interacting parts, say Woese and Goldenfeld, and understanding it demands a detailed exploration of the self-organising potential of such a system. On the basis of their studies, they argue that horizontal gene transfer had to be a dominant factor in the original form of evolution.

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