Dog domestication and the dual dispersal of people and dogs into the Americas

Abstract

appears to be extinct (1, 14, 15). Finally, genetic and archaeological evidence from modern and ancient dogs and wolves demonstrates that dog domestication took place in Eurasia (16–18). Many other aspects of dog domestication, including the circumstances under which the relationship began, the time frame, and the number and location(s) of potential independent domestication regions, remain unresolved (19–21). The shift in human–wolf interactions that led to domestication has been addressed through a wide variety of approaches, and there are ongoing debates over when the first recognizably domestic dog appeared. The earliest generally accepted dog dates to ∼15 ka (from the site of Bonn-Oberkassel, discussed below). However, claims for the existence of domestic dogs as early as 40 ka (22–28) have been made on the basis of morphological (22, 24–27), isotopic (22, 29), genetic (22, 28, 30), and contextual assessments (24, 31) of ancient canid remains. Yet, none of these potential domestication markers is fail-safe, owing to the fact that wolves and early domesticated dogs can be difficult to distinguish from each other. For example, common morphological markers used to identify domestication such as tooth crowding, skull size, and reduced snout length often fail to clearly distinguish dogs from wolves (32–36). Isotopic signatures, and their dietary inferences, have been used to identify early dogs, though these have also been questioned given that the isotopic variation is often consistent with wolf diets (3). In addition, genetic analyses of these proposed early dogs have demonstrated that they do not belong to the same lineages as ancient or modern dogs (30, 37). While genomic estimates from multiple studies place the split time within wolf lineages, including the one that ultimately gave rise to dogs, to between ∼40 and 27 ka (14, 38), this timing is unlikely to reflect the initiation of the domestication process (1, 39). Finally, sites with purported domestic dogs have been questioned based on an absence of carnivore gnawing (40) or pups (41), features taken to indicate the presence of a living, breeding dog population. Accordingly, claims for domestic dogs at the Belgian site of Goyet (22, 42, 43) have been disputed since their cranial and