Nature Genet. 32, 153–159 (2002).

By error, several corrections were not made to proofs while preparing the manuscript for the press.

In the reference list, reference 25 (Losman et al.) should be inserted as reference 13. As a consequence, references 13–24 should be renumbered as 14–25.

In the text, the following changes should be made:

On page 154, in the second column, reference 16 should be placed at the end of the sentence “These observations underscore the selective advantage...”. Reference 16 should also be removed from the first line on page 155.

On page 155, in the second column, reference 17 should be placed at the end of the sentence “'Cold' and 'hot' spots for transposon insertions...”.

On page 157, in the first full paragraph, reference 17 should be reference 18, reference 18 should be reference 19, reference 19 should be reference 20, and reference 25 should be reference 21.

On page 158, in the first full paragraph, references 21–23 should be references 22,23.