Genalogical and historical DNA.
Genealogical DNA has taken great steps forward the last 10 years. DNA; autosomal, yDNA (Y Chromosome) and mtDNA (mitocondrial), create new insigths in combination with traditional genealogical sources, e.g. Chruch records. Genealogical DNA also challenges and extends historical knowledge and sources on migration.
However, we must keep in mind that all (most?) test taken are taken by current, living persons. Historical patterns of migration that we “see” are inferred from current geographic location of the persons tested, or his/hers more recent ancestry. “Hot spots” of certain haplogroups may appear due to variation in number of tests. The representativity of genalogical DNA is hard to calculate and evaluate. In scientific studies much effort is put into the selection process to achieve valid and representative data.
Genealogical DNA can be validated thru various methods, e.g. traditional genealogy and multiple tests on known and verified genealogy (branch testing, sibling split)
Read the following posts on “Historical DNA” with care and a critical and open mind.