In my previous post on Finnish population clustering I should have emphasised that the map was constructed only from individuals who had both parents from the same geographic/linguistic region; this obviously provides a lot more power to detect a correlation.
The close match between genetic and geographic ancestry in these selected individuals indicates that there hasn’t been a huge amount of long-range admixture between Finnish populations over quite a long period of time – if there had been, there would be no reason to expect much correlation between the two maps. However, data in the supplementary section of the paper show that there has been substantial mixing over more recent history:
This graph shows the number of individuals from the cohort that had both parents from a single region. You can see immediately that the single largest category is the “mixed” category indicating parentage that crosses region boundaries. It seems likely that many of these individuals come from border areas between the regions (in which case excluding them from the map will have resulted in a rather artificial increase in the separation between clusters), but no doubt there are also many examples of long-range admixture resulting from increases in population mobility during the 20th century.
As mobility continues to increase the correlation between geographical location and genetic ancestry will decline rapidly. We really are in a brief and privileged moment in time: a moment when we have the tools to perform genome-scale analyses of ancestry, but before globalisation [and urbanisation] begins to erase information about historical population structure.
Chiara Sabatti, Susan K Service, Anna-Liisa Hartikainen, Anneli Pouta, Samuli Ripatti, Jae Brodsky, Chris G Jones, Noah A Zaitlen, Teppo Varilo, Marika Kaakinen, Ulla Sovio, Aimo Ruokonen, Jaana Laitinen, Eveliina Jakkula, Lachlan Coin, Clive Hoggart, Andrew Collins, Hannu Turunen, Stacey Gabriel, Paul Elliot, Mark I McCarthy, Mark J Daly, Marjo-Riitta J√§rvelin, Nelson B Freimer, Leena Peltonen (2008). Genome-wide association analysis of metabolic traits in a birth cohort from a founder population Nature Genetics DOI: 10.1038/ng.271