 In 2002 Thomas coauthored a paper providing Y chromosome evidence for a very high Anglo-Saxon component of patrilineal ancestry in central England.This result proved unpalatable for many archaeologists and led to Thomas developing the "apartheid-like social structure" model to explain the discrepancy between archaeological and genetic estimates of the scale of Anglo-Saxon migration.Thomas has also worked extensively on the evolution of lactase persistence (see Lactose intolerance), the ability of some humans to produce the enzyme lactase throughout their adult life and thus to consume appreciable quantities of fresh milk without the discomforts of lactose malabsorption.