Geographic locations associated with each country were assigned using the central point of the geographic area of the country (Supplementary Table 3). Three exceptions are the Russian Federation, Sweden and Norway, where the geographic locations were assigned to the location of the capitals of these countries (because central points were assumed to not be as reflective of the probable origins of these individuals). Within Switzerland, we represent the Swiss-French with the geographical coordinates of Geneva, the Swiss-German with those of Zurich, and Swiss-Italian with those of Lugano. Distances between points are always calculated as great circle distances.
