Mrs Kiwi:
This doesn't directly answer the article that Canadian Steve posted in #402 but it does discus the mechanism of evolution. This is not the whole article. If you would like it i can email it to you. It was too long to post it all and the New Scientist Achive is only accessable to members. Although they do have a 7 day free trial thing if you really want it online.
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"Ready, steady, evolve </td></tr> <tr> <td>
New Scientist vol 175 issue 2362 - 28September2002, page 28 </td></tr> <tr> <td class=space8></td></tr> <tr> <td>
Evolution is a slow, painstaking process. But have plants and animals found a way of seizing the throttle to get them out of a tight spot? Bob Holmes reports </td></tr> <tr> <td class=space8></td></tr> <tr> <td> DESPITE its universal role in biology, evolution still poses some pretty perplexing questions. Take changes in body form. Every tree or beetle or mouse looks the way it does because thousands of genes turned on at exactly the right time and place to guide the organism from single cell to adulthood. But if body plans are the product of such intricately orchestrated programs, how can evolution ever conjure up new ones? Any slight perturbation would surely send a species tumbling from its evolutionary peak into the barren valleys beneath. Plants and animals may have hit on an ingenious solution - bottling up evolution for times when they really need it. By squirrelling away genetic mutations, the raw material of evolution, and releasing them all at once, species may be able to leap from peak to evolutionary peak without ever having to slog through the valleys between. This happy knack increases their odds of surviving stressful conditions - nothing less than evolution on demand. On the face of it, the idea sounds like biological heresy. Plants and animals couldn't have that sort of control over the random process underlying evolution, could they? Surprisingly, they could. Over the past few years, a handful of lab experiments have thrown up convincing evidence that organisms really can save up mutations for a rainy day. If the same thing happens in nature, then plants and animals have hit on a way to seize the throttle of evolution, accelerating it when necessary and slowing it down when not. Their storehouse of mutations may also prove to be a treasure trove of new genes for drug hunters to plunder or, equally, the time-bomb that helps explain the diseases of old age. The lead actor in this iconoclastic drama is a so-called "chaperone" protein called hsp90. One of the most abundant proteins in animals, plants and fungi, hsp90's job is to bind to unstable proteins and help them maintain their correct shape. In this role, hsp90 is rather like a valet, tidying up proteins that would otherwise become dishevelled by environmental insults such as high temperatures. Hence the chaperones' other name, "heat shock proteins". But hsp90 is also a crucial regulator of development. As a way of silencing proteins until their services are required, cells deliberately make some proteins unstable, especially certain ones that regulate developmental pathways. One of hsp90's jobs is to hold some of these proteins in the "standby" position. "It works on just about every [developmental] pathway you can imagine," says Susan Lindquist, director of the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts. The first hint that hsp90's job gives it unusual leverage over evolution came four years ago, when Lindquist and her team mate Suzanne Rutherford were working at the University of Chicago. They noticed that fruit flies carrying a mutant copy of the
hsp90 gene sometimes had offspring that looked very weird indeed. "We had eyes that grew out from the head in a stalk-like pattern, we had bristles in the wrong places, wings with different venation patterns and shapes, abdomens that were partly folded over, legs that were different shapes - virtually every structure in the adult fly was affected," says Lindquist. The same abnormalities showed up in normal flies doped in the larval stage with geldanamycin, a drug that interferes with the action of hsp90 (
Nature, vol 396, p 336). .........."</td></tr></tbody></table>
