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Of Mice and Men and the March of Science
Published on Monday, February 12, 2001 in the Independent / UK
Human Genome Project
Of Mice and Men and the March of Science
by Andrew Brown
Doesn't science march quickly? Only last summer, when it was announced that the human genome had been almost completely decoded, every news report explained that there were 60,000 genes in it. Now they have counted them all, and what do you know, there are only 30,000 after all. It looks as if they have been counting the genes in a sock drawer, so every time they pick one up, another slithers out the crack in the back.

Thirty thousand genes is still an enormous number, of course; but it's only 300 more than you need to build a mouse. It was enough of a blow to human pride to discover that we share 98 per cent of our genes with chimpanzees. To discover that we are only marginally more complicated than a mouse is horrendous.

But with any luck, the news will come as a real blow to the quasi-mystical faith in DNA that has grown up over the last 30 years. All the rhetoric about the book of life was very useful. It made possible the funding of the effort to sequence DNA. But it was also deeply bogus: what has been discovered is not the text of the book of life, but its vocabulary.

To look at the human genome and say that we now know what is necessary for a human being, is like listing the 25,000 words that Shakespeare used, and saying that this tells us how to write his plays.

The analogy is not as far-fetched as it may seem. With genes, as with words, we are interested in their meaning, not in isolation, but as it emerges from their interplay with the world and with each other. If Hamlet and Love's Labour's Lost, say, were to use exactly the same number of words, would this make them equally complex?

The second point about having only a few more genes than mice, is that mice themselves are extremely complex creatures. Almost anything alive is more complicated than we can imagine. Even the nematode worm, C. elegans, which is about as boring as anything can be yet still be recognisably alive, has preoccupied some of the best minds in the business for some 30 years. There is a man at Massachusetts Institute of Technology who has spent almost all that time studying 23 cells in the worm's vulva: these things do hold on to their secrets.

And though the worm does not do anything we might envy – it spends its life in dungheaps, munching bacteria – you can have a better life with very few genes indeed. The fruit fly has fewer genes even than the worm – about half as many as we do – but it can fly and walk up walls: we haven't gained much with our increasing complication.

Most of the confusion arises from a simple metaphor. People talk about genes as "blueprints" for grown-up organisms. But if they were blueprints, we wouldn't need to go to all this trouble to discover them. With a blueprint, you always know which bit of the plan corresponds to which bit of the building. Genes, as Richard Dawkins first pointed out, are more like recipes. If you change them, you change the outcome, but not in predictable ways. What is more, the ingredients in a recipe can be combined in different ways for different results. Without the cooking instructions, you know only half of what you need.

The point of all this is to point out what all the researchers know: that genes themselves are no more interesting than Hittite vocabulary. What is interesting and difficult is how they are used by the cells around them to make the proteins that everything else is made of. Complete understanding of that is some way off, even with the worm; discovering that we have only 30,000 genes just means that they must interact in even more fiendishly complex ways.

But, luckily for medicine, we don't need to understand something completely in order to understand enough to fix it.

© 2001 Independent Digital (UK) Ltd.


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