AbstractAlthough in Drosophila pair‐rule genes play crucial roles in the genetic hierarchy that subdivides the embryo into segments, the extent to which pair‐rule patterning is utilized by different arthropods and other segmented phyla is unknown. Recent data of Dearden et al.1 and Henry et al.,2 however, hint that a pair‐rule mechanism might play a role in the segmentation process of basal arthropods and vertebrates. BioEssays 25:425–429, 2003. © 2003 Wiley Periodicals, Inc.