Pushing back the expansion of introns in animal genomes

In a recent paper in Science, Raible et al. (2005) surveyed the position of introns in 30 genes of a marine annelid and showed that over 60% of the introns occupy positions identical to those in human homologs. In contrast, both human and marine annelid genes share only 30% of their introns with other invertebrates. These observations suggest that the common ancestor of most animal phyla had intron-rich genes and reinforce the notion that introns proliferated early in the evolutionary history of eukaryotes.