WASHINGTON (AP) — Clues to the mystery of why Viking colonies in Greenland flourished and fell have been found in the DNA of medieval walrus bones housed in more than a dozen European museums.

For almost 500 years, the Norse descendants of Erik the Red built churches and manor homes and expanded their settlements on the icy fringes of European civilization. On Greenland, they had elaborate stone churches with bronze bells and stained glass, a monastery, and their own bishop. Their colonies at one time supported more than 2,000 people.

And then they vanished.

Scholars have long wondered why. "W...