Until recently, the prehistory of Wales was portrayed as a series of successive migrations. The present tendency is to stress population continuity; the Encyclopedia of Wales suggests that Wales had received the greater part of its original stock of peoples by c.2000 BC. Recent studies in population genetics have argued for genetic continuity from the Upper Paleolithic, Mesolithic or Neolithic eras. According to historian John Davies, the Brythonic languages spoken throughout Britain resulted from an indigenous "cumulative Celticity", rather than from migration.