Genetic research shows a strong similarity between the Y chromosome haplotypes of Irish men with Gaelic surnames and males from the area of Spain and Portugal, especially Galicia, Asturias, and Cantabria (and perhaps former Basque country). The incidence of the R1b haplogroup is 70% or more in Celtic regions – Cumbria and Cornwall in England, the Celtic Northern region in Portugal (Douro Litoral, Minho and Trás-os-Montes e Alto Douro), northern Spain (Celtic Galicia, Asturias, León, Cantabria and Basque Country), western France (Béarn, Gascony, Guyenne, Saintonge, Angoumois, Aunis, Poitou, Touraine, Anjou and the Celtic Brittany), and Celtic Countries – Wales and Scotland in Britain. R1b's incidence declines gradually with distance from these areas but it is still common across the central areas of Europe. R1b is the most frequent haplogroup in Germany and in the Low Countries, and is common in southern Scandinavia and in northern and central Italy. This led writers, such as Stephen Oppenheimer and Bryan Sykes, to conclude that the majority of Irish people primarily descend from an "Iberian refugium" population bottleneck dating back to the last ice age.