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Wednesday, November 25, 1998 Published at 18:33 GMT


Mechanism for evolution described

The flies displayed a variety of different body shapes

By BBC News Online Science Editor Dr David Whitehouse

Scientists have discovered what they believe may be the molecular basis of evolution.

They may have found out what actually happens to an organism's genes that enables its offspring to adapt and change - that is to evolve into new types of living creatures.

The researchers at the University of Chicago say that although an organism's DNA is changing over time, many of the individual, small genetic variations just accumulate and only become noticeable when that organism is under environmental stress.

You can look at it this way: while an animal may be perfectly adapted to its environment, behind the scenes redundant copies of its genes are mutating.

Only when the creature's environment alters and it needs to adapt to the changing conditions do these mutations come to the fore.

Essence of evolution

Most mutations will be harmful and will not help the creature survive better. But some mutations just might provide an edge.

This is the essence of evolution - creatures have to adapt to changing conditions. Those that have an edge will survive - those that do not will perish.

"For the first time we have a molecular mechanism that explains how organisms that have stuck to the same shape for eons can evolve new traits that help them adapt to changing conditions," says Susan Lindquist, professor of molecular genetics & cell biology at the University of Chicago.

The way cells do this is by using molecules called heat shock proteins, in particular Hsp 90. Usually this molecule helps other molecules in the cell to cope with heat.

But when an organism is under particular stress and has to cope with a changing environment, it appears that Hsp 90 gets called away from its normal duties and many of the genetic mutations that had hitherto been masked suddenly break out.

These can then be passed onto the organism's offspring to produce changes in body plan.

New environment

"This sounds like a very bad thing, and no doubt it is for most of the individuals," says Lindquist. "But for some, the changes might be beneficial for adapting to a new environment."

Lindquist and Suzanne Rutherford, a postdoctoral fellow, demonstrated that reducing levels of Hsp 90 allowed natural genetic abnormalities hidden in fruit fly populations to suddenly appear.

They produced flies with eyes of different colours; deformed in shape or absent; flies with misshapen legs; flies with small or absent wings, and so on.

Lindquist speculates that Hsp 90 may be a key player in controlling the alternation between long periods of genetic stability and the sudden bursts of change seen in the fossil record during times when the Earth was undergoing major climate changes.

"The way that Hsp 90 covers and uncovers hidden genetic variations provides a very plausible molecular mechanism for evolution, but proving that it actually works over long timescales will be no easy task," she says.

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