Scandinavian stock. The strength of this argument is the almost total replacement of pre-existing place names by those of Norse origin throughout much of the region. Its weakness is that the place name evidence is from a relatively late date and the nature of this transition remains controversial. Genetic studies show that Shetlanders have almost identical proportions of Scandinavian matrilineal and patrilineal ancestry, suggesting that the islands were settled by both men and women in equal measure. The pagan reaction hypothesis proposed by Bjørn Myhre suggests a long tradition of mobility amongst the various populations of the North Atlantic seaboard and that the expansion of Christian missions resulted in ethnic tensions that led to or exacerbated Viking expansion. There is some evidence of such mobility, such as Irish missionary activities in Iceland and Faroe Islands in the 8th century, but little that is conclusive. The fourth suggestion is the Laithlind or Lochlann hypothesis. This word appears in various forms in the early Irish literature and is usually assumed to refer to Norway itself, although some have preferred to locate it in the Norse-dominated parts of Scotland. Donnchadh Ó Corráin is a proponent of this view and claims that a substantial part of Scotland—the Northern and Western Isles and large areas of the coastal mainland—were conquered by the Vikings in the first quarter of the 9th century and that a Viking kingdom was set up there earlier than the middle of the century. Essentially a variant of the earldom hypothesis, there is little archaeological evidence in its favour, although it is clear that extensive Viking incursions on the Irish coasts were supported by a presence of some kind in the Hebrides, even if the date the latter became prominent is far from certain. As Ó Corráin himself admits "when and how the Vikings conquered and occupied the Isles is unknown, perhaps unknowable". Early Viking incursions Norse contacts with Scotland certainly predate the first written records in the 8th century, although their nature and frequency are unknown. Excavations at Norwick on the island of Unst in Shetland indicate that Scandinavian settlers had reached there, perhaps as early as the mid-7th century, consistent with dates produced for Viking levels at Old Scatness. From 793 onwards repeated raids by Vikings on the British Isles are recorded. "All the islands of Britain" were devastated in 794 with Iona being sacked in 802 and 806. (These