There is intense debate over the role the Arabian played in the development of other light horse breeds. Before DNA-based research developed, one hypothesis, based on body types and conformation, suggested the light, "dry", oriental horse adapted to the desert climate had developed prior to domestication; DNA studies of multiple horse breeds now suggest that while domesticated horses arose from multiple mare lines, there is very little variability in the Y-chromosome between breeds. Following domestication of the horse, due to the location of the Middle East as a crossroads of the ancient world, and relatively near the earliest locations of domestication, oriental horses spread throughout Europe and Asia both in ancient and modern times. There is little doubt that humans crossed "oriental" blood on that of other types to create light riding horses; the only actual questions are at what point the "oriental" prototype could be called an "Arabian", how much Arabian blood was mixed with local animals, and at what point in history.