Fossils found at Zhoukoudian, China, have suggested to archaeologists such as Stanley Olsen, author of Origins of the Domestic Dog, that wolves and Homo erectus were at least working the same terrain as early as 500,000 years ago. The remains of wolves and Homo erectus dating to around 300,000 years ago have also been found in association with each other at Boxgrove in Kent, England, and from 150,000 years ago at Lauzerte in the south of France. It seems more likely that this omnivorous biped, with its tools and weapons, lived and hunted in proximity to that consummate social hunter, the wolf, through much of Eurasia, than that their bones simply fell into select caves together. Who scavenged from whom, we cannot say.
Wolves were far more numerous then than now, and they adapted to a wide range of habitats and prey. On the Eurasian steppes, wolves learned to follow herds of ungulates—in effect, to herd them. Meriwether Lewis observed the same behavior during his journey across North America in the opening years of the 19th century; he referred to wolves that watched over herds of bison on the Plains as the bisons’ “shepherds.” Of course, those “shepherds” liked it when human hunters attacked a herd because they killed many more animals than the wolves, and although the humans carried off the prime cuts, they left plenty behind.
Ethologists Wolfgang M. Schleidt and Michael D. Shalter refer to wolves as the first pastoralists in “Co-evolution of Humans and Canids,” their 2003 paper in the journal Cognition and Evolution. Early humans, they argue, learned to hunt and herd big game from those wolves; thus, the dog emerged from mutual cooperation between wolves and early humans, possibly including Neanderthal. There is no evidence yet of Neanderthal having tame wolves, much less dogs, but the larger point is that when modern humans arrived on the scene, they found wolves already tending their herds, and they immediately began to learn from them. That was long before humans began, in some parts of the world, to settle into more permanent villages, some 12,000 to 20,000 or 25,000 years ago.
Schleidt and Shalter based their model on wolf behavior and on genetic studies that have consistently shown that dogs and wolves diverged between 40,000 and 135,000 years ago. The first of those studies emerged from the lab of Robert K. Wayne, an evolutionary biologist at the University of California at Los Angeles who had already made headlines by showing definitively that the dog descended from the wolf alone. In a paper appearing in the June 13, 1997, issue of Science, Wayne and his collaborators said that dogs could have originated around 135,000 years ago in as many as four different places. They also argued that genetic exchanges between wolves and dogs continued—as they do to this day, albeit in an age during which dogs have become ubiquitous and wolves imperiled.
Since that paper appeared, the dog genome has been fully sequenced and provides a time frame for domestication of 9,000 generations, which the authors of a paper on the sequencing in the December 8, 2005, issue of Nature pegged at 27,000 years. But except for that, subsequent studies of mitochondrial DNA, which is most commonly used to date species divergence, have pointed to a time frame of 40,000 to 135,000, with 40,000 to 50,000 years ago looking like the consensus date.
Most of this work has been conducted in Wayne’s lab; in the Uppsala University lab of Carles Vilà, his former student and the lead researcher on the 1997 paper; and in the lab of Peter Savolainen of the Royal Institute of Technology, Stockholm, another collaborator on the original paper.
A signal problem with the early date is that it doesn’t appear to match the archaeological record. The dog is not only behaviorally but also morphologically different from the wolf, and such an animal first appears in the fossil record around 14,000 years ago in Bonn-Oberkassel, Germany. Archaeologists nearly universally peg the origin of the dog to that time.
Wayne, Vilà and their supporters have suggested from the start that behavioral change could predate morphological change, which would have occurred when humans began to create permanent settlements, thereby cutting—or at least reducing—their wolf-dogs’ contact with wild wolves. People might also have begun attempting to influence the appearance of their dogs at this point.