Sampling Design and the Genetic Reconstruction of the Slavic Migration: A Critical Reading of Olalde et al. (2023) and Gretzinger et al. (2025)

Two influential ancient DNA studies, Olalde et al. (2023) and Gretzinger et al. (2025), describe the early medieval spread of Slavic speakers as a large, largely one-directional movement from north to south. This article re-examines both against their own supplementary data. In each, the proxy for the incoming population is sampled at the destination rather than the source, and in one case postdates the movement it measures by two centuries; compared samples differ in settlement type and burial context; and several accepted models pass only narrowly, with error margins omitted from the headline figures. The earliest directly dated carrier of I2a-Din, treated in both as a Slavic marker, is a seventh-century burial in Dalmatia, three centuries before any northern carrier. Written sources place politically differentiated Slavic groups on the Danube before the earliest sampled horizon. None of this denies demographic change. It suggests that its scale, direction and timing are less securely established than the published figures imply.