The second world war left a major mark on the genetic composition of Finland, researchers have found, though the work may not have included minority ethnic groups.
Matti Pirinen at the University of Helsinki, Finland, and his colleagues looked at the genomes of around 18,500 people to study how the genetic composition of 10 populations across 12 geographic regions covering most of Finland changed between 1923 and 1987.
“We can really see with an accuracy of one year how the genetic structure has changed in Finland during the last century,” says Pirinen.
The team found that urbanisation has caused some changes in the genetics of people in Finland. But the biggest impact, increasing the number of regions each individual could trace their ancestry to, came after the forced movement of people from Finnish Karelia to the rest of the country in 1940, following a peace treaty with the Soviet Union during the second world war.
The researchers chose the genomes of 2741 individuals who were born and whose parents were born within the 12 regions to form the basis of the 10 populations they studied. This definition could skew the results, says Eran Elhaik at Lund University in Sweden.
“Identifying people who lived closely next to each other as the most homogeneous people raises the question of how these people became so homogeneous,” says Elhaik. “These are likely farmers who have married each other for a very long time. What makes them represent the ancestors of Finns better than any other people in Finland?”
The researchers say that their populations probably don’t cover all relevant sources of genetic ancestry, such as minority ethnic groups, because it is likely that only a small number of individuals from these groups were included in the study. Individual data was pseudonymised, meaning it isn’t possible to know for sure, say the researchers, and they note that the study shouldn’t be used to define who is Finnish, in a social, legal or cultural sense.
Elhaik says this uncertainty over minority ethnic groups limits what the study can tell us about the Finnish population as a whole. “Focusing on a small data set of 10 per cent of the population carves Finns’ image as genetically homogeneous people. What about the rest of the people who are of more mixed origins and are not well represented by the model? No population is an island,” he says. “This method is not applicable to mixed individuals, which represent a growing proportion of individuals in any society.”
Journal reference: PLoS Genetics, DOI: 10.1371/journal.pgen.1009347
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