Exactly one year ago this week, scientists announced that they had finished the 'Book of Life'. The complete sequence of the human genome had been painstakingly reduced to an ordered list of letters representing the four bases of DNA. This text was believed to be virtually identical for every person on Earth — and the major differences between individuals, such as hair colour, were said to be the equivalent of typographical errors, no longer than a single letter. The next major task for scientists was to find out which of these tiny differences can cause disease. But even as the ink was drying on the complete sequence, some researchers were questioning whether there was really such a thing as the definitive edition of the Book of Life. By skim-reading individual genomes, these scientists were finding bizarre and unexpected irregularities. In some people, whole paragraphs of the text were duplicated, whereas in others, large passages were missing, or even printed backwards. These major revisions turned up in air kinds of people, including many who seemed healthy and normal. Suddenly, it seemed possible that there was actually no standard version of the Book of Life, and researchers wondered whether we are all much more different from each other than they had thought.
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