Barrier analysis revealed genetic barriers between Finland, Italy and other countries, as has been described before [12]. Interestingly, barriers could be demonstrated within Finland (between Helsinki and Kuusamo) and Italy (between northern and southern part). Another barrier emerged between the Eastern Baltic region and Sweden, but not between the Eastern Baltic region and Poland (Figure S4). The barrier between Bulgaria and Western Russia, Poland and Lithuania may have arisen due to the fact that several populations are missing in between those countries. It has been shown previously that the populations of central European background are less differentiated genetically, whereas the Finns exhibit a more homogeneous population structure with decreased genetic diversity [17], [25].
