It it is not at all clear, however "who got there first", and as far as I can see, the evidence just tells us there is a substantial east-west difference in Y-chromosomes in Finland, it doesn't really tell us which of the two elements represents the most ancient stratum.
In my opinion, the Finnish gene pool may contain traces of the aboriginal inhabitants, as well as the later eastern elements which brought the Finnish language, and the later still influences by Germanic Scandinavians. Hopefully the northern cold has been generous with DNA preservation and we may get some direct glimpses into the country's genetic history.
Some related posts:
- Genomic substructure in Finns
- Migrations in the Baltic region inferred from Y chromosomes and mtDNA
- Y chromosome variation of Finns
European Journal of Human Genetics doi:
Genetic markers and population history: Finland revisited
Jukka U Palo et al.
The Finnish population in Northern Europe has been a target of extensive genetic studies during the last decades. The population is considered as a homogeneous isolate, well suited for gene mapping studies because of its reduced diversity and homogeneity. However, several studies have shown substantial differences between the eastern and western parts of the country, especially in the male-mediated Y chromosome. This divergence is evident in non-neutral genetic variation also and it is usually explained to stem from founder effects occurring in the settlement of eastern Finland as late as in the 16th century. Here, we have reassessed this population historical scenario using Y-chromosomal, mitochondrial and autosomal markers and geographical sampling covering entire Finland. The obtained results suggest substantial Scandinavian gene flow into south-western, but not into the eastern, Finland. Male-biased Scandinavian gene flow into the south-western parts of the country would plausibly explain the large inter-regional differences observed in the Y-chromosome, and the relative homogeneity in the mitochondrial and autosomal data. On the basis of these results, we suggest that the expression of 'Finnish Disease Heritage' illnesses, more common in the eastern/north-eastern Finland, stems from long-term drift, rather than from relatively recent founder effects.