On his Gene Expression blog, Matt McIntosh discusses the intertwined roles of retrotransposons, non-coding DNA, and adaptive evolution. Eukaryotic genomes have transposons that duplicate and move around and sometimes take bits of genes with them, for good, bad, or neutral affect on the organism. McIntosh then theorizes that adaptive evolution accompanied by duplication events should correlate with more leftovers from transposition events. But he's not quite sure how to test that idea.