There has clearly been a differential (geographic/time) transition of treponemal disease in the southwest. The patterns of disease reproducibly fulfill criteria for yaws (present initially), with subsequent recognition of syphilis. Syphilis appears to be a North American disease, which developed as a mutation from yaws approximately 2000 ybp on the Colorado Plateau. The time course of subsequent replacement of yaws by syphilis varies above and below the Mogollon Rim and appears compatible with timing of increasing social interactions between the groups