The evolutionary history and relationships of North American species are considered in light of various lines of evidence and especially that from mating call structure and genetic compatibility. The approximately 30 species fall into 11 species groups, which appear to be clusters of relatively recently evolved species. Most of the species groups fit clearly into one or the other of two major evolutionary lines which seemingly correspond to two major lines in Eurasia and result from the invasion of North American by both. One line, represented in southern Asia by B. melanostictus is mainly southern in distribution with the marinus group as one New World branch and a complex of species groups (valliceps, coccifer, canaliferus, occidentalis, punctatus-marmoreus, and possibly cognatus) as the other. The second line, represented by B. calamita and relatives in temperature Eurasia, is represented by the boreas and americanus groups of temperate North America, and the debilis and quercicus groups possibly belong with this line. Fertile intragroup hybrids have been demonstrated where it has been possible to test by backcrossing. Metamorphosis of reciprocal intergroup hybrids has been shown in various combinations of species belonging to the same major line but not between groups belonging to different major lines. All intergroup hybrids tested have proved sterile.