770,000 Americans Took a DNA Test — The Map Still Shows Where Their Families Stopped in the 1800s

Most people buy a DNA test to find out which part of Europe, Africa, or Asia they came from. In 2017, a team led by Eunjung Han at AncestryDNA asked a different question: forget the continents — what does American DNA say about America itself? They took 770,000 consenting genotyped individuals, mapped more than 500 million identity-by-descent connections between them — shared stretches of DNA inherited from a recent common ancestor — and annotated the resulting network against a database of over 20 million genealogical records. Published in Nature Communications, it remains one of the most detailed portraits ever made of a country's internal population structure.