Even a blind chicken finds a kernel of corn...

but it is difficult for 23andme if it is question about Finnish ancestry.   A new version of the Ancestry composition tries to figure out ancestry in countries and 23andme found two ancestral locations in Finland:  Uusimaa and Swedish speaking Ostrobothnia.  First, Uusimaa was over decades a region under scientific debate because of its extremely sparse prehistoric population and historians and archaeologists were pondering reasons.  Uusimaa was mostly hunting grounds of Tavastians until the Swedish migration in the 14th century. Secondly, the Swedish speaking Ostrobothnia was repopulated by Swedish migrants at the same time as Uusimaa, in the beginning of the Swedish era in Finland.  Today those Ostrobothnians are descendants of those Swedish migrants and older Finnish people.  Finnish root populations could be easily determined by archaeological and linguistic reasons, but 23andme wiseguys make their calculations and brilliant observations at their gene lab and don't need any outside help.