my deliberately simplified example we were dealing with just one segment of DNA on an island originally settled by only one couple. No one arrived or left for millennia. It doesn’t get any simpler than that.
Let us now suppose that other things happened on the island. Perhaps half the population died in an earthquake, or the central volcano erupted, destroying the crops, and three-quarters of the people starved, or an epidemic killed 90 per cent of the population. These are the sorts of catastrophes which might have happened in real life. Those events can severely distort our calculations. For instance, and let’s make it extreme, a tsunami kills everybody on the island except a couple who were far out to sea fishing at the time. They survived and, over time, their offspring repopulated the island. In this scenario, the genetic calculations would give the time that had elapsed since the tsunami rather than since the original settlement. The island would have undergone a ‘population bottleneck’. There would be no way of telling, by genetics alone, for how long the island had been settled before the tsunami struck. If we introduce further complexity, like a few boatloads of new arrivals, then all hope of being precise about the original settlement date goes up in a puff of smoke.
Given these unknown and often unknowable factors, I take claims of accurate genetic dating of past events with a large pinch of salt. That does not mean they lack value, but it is a mistake to become a slave to such calculations. We will use the island metaphor again when we come to consider the origins of pedigree dog breeds. Wayne and Vilà also used this kind of calculation to estimate the timing of the wolf–dog transition. The answer was much further back than anyone suspected, between 76,000 and 135,000 years ago.
6
At some point in the past the lives of wolf and human became intertwined and it is from this partnership that the dog eventually emerged. Until genetics entered the fray, the only way of following this transition through the intervening millennia was through fossils. Good fossils are in short supply and the fossil record is understandably full of gaps.
In terms of time, the oldest skulls that could even remotely be differentiated from wolves were excavated in the Goyet cave in southern Belgium in the 1860s. Like all good fossil sites, Goyet is a limestone cave whose alkaline environment helps to preserve the calcified bones and, importantly, any DNA that might lie within.
From studying the style of stone and bone tools found there, it was clear that the cave had been occupied by humans for a very long time. Neanderthals lived there during the time of the Mousterian culture, which lasted from about 160,000 years to 40,000 years BP (the standard archaeological abbreviation for ‘before present’). It takes its name from the rock shelter at Le Moustier in the Dordogne region of central France. The Mousterian lasted until the arrival of modern humans, our ancestors, about 40,000 years ago. As is not uncommon with early excavations, disturbance of the layers within the cave made precise stratigraphic dating of the different artefacts found there problematic. However, carbon-dating of the fossils gave precise dates for the organic remains at least. The cave fauna was a rich assemblage of cave bear, cave lion, horse, reindeer, lynx, red deer and mammoth. In the deeper recesses of the cave archaeologists found the skull of a ‘large canid’ carbon-dated to 31,700 years BP. Was it a wolf or was it a dog?
Of course, there must have been a period after the first wolf was adopted into a human band when its skull was exactly the same as a wolf’s – because it was a wolf. There was no exact moment of transition from one to the other, and the whole debate has a strong flavour of semantics. The more cautious authors merely refer to these intermediates as ‘canids’ or ‘wolf-dogs’, thereby sidestepping the argument altogether.
A similar conundrum faced archaeologists excavating the nearby site of Trou des Nutons, a cave formed in the limestone hills of the Ardennes by the River Lesse, a tributary of the Meuse. Among the fossils found in the Trou des Nutons were beaver, roe deer, horse, bison and wild sheep, suggesting a later occupation than at Goyet. This was confirmed when another skull of a mystery ‘large canid’ was given a carbon date of 21,800 years BP. This is a surprisingly early date and in the middle of the last Ice Age. But was it the skull of a dog or a wolf?
These skulls from France were subjected to a series of precise measurements of snout-length and width, the length of the tooth row and the size of the flesh-shearing, self-sharpening carnassial teeth that wolves and dogs have where we have molars.
Fossil canid skulls from two archaeological sites in Russia and Ukraine, one at Mezin (Ukraine) and the other at Avdeevo just over the Russian border, were given the same treatment. These two sites were inhabited by early humans who constructed huts of mammoth bones and left behind an abundance of beads and other artefacts carved from mammoth ivory. The objective of the osteometric study of candid fossils from these two sites was to discover whether the remains of these ‘large canids’ differed sufficiently from wolves in their skull morphology to be classified as dogs on their way to domestication rather than unmodified wolves.
To complete the comparisons, the analysis was extended to include later, but still prehistoric, unambiguous fossil dogs from France and Germany. Also included were a selection of modern and fossil wolves from Europe and Asia along with modern dogs from several large breeds including Great Dane, Tibetan Mastiff, Siberian Husky, Chow Chow, Irish Wolfhound, Malinois, Dobermann Pinscher and German Shepherd.1
Comparing multiple skull measurements from dogs of different sizes is a complicated business, and I will spare you the details of the multivariate analysis and go straight to the main conclusion. The Palaeolithic skulls from the oldest sites, including Goyet at 31,700 years BP, had a significantly different shape from modern, or indeed fossil, wolves. This suggests that, even by that early date, these animals were dogs already on the way to modification through ‘domestication’. An alternative explanation, though in my opinion rather less likely, is that these were the skulls of one or more wolf species that later became extinct. As we shall see later, there is other enticing evidence to support the former scenario and suggest that the close association between wolf and man began a very long time ago.
The next layer of evidence about the changing appearance of domesticated dogs comes from the late glacial period around 17,000 years BP, when the ice sheets covering northern Europe were fast retreating. The shrinking tundra no longer supported herds of large prey animals. The climate warmed considerably, rainfall increased and forests covered much of the formerly open tundra. The fauna changed with the landscape and many prey animals disappeared. Mammoths, woolly rhinoceros and their predators, the sabre-tooth tiger and cave bear, were forced into extinction. Others, like the wild horse, reindeer and bison, shifted their ranges. Humans began to spread north, first following the shrinking herds and later, as they entered the Mesolithic period, changing their diet to smaller woodland prey, like wild boar, pine marten, red and roe deer. On the coastal settlements, shellfish became a major source of food and the first boats ventured out to sea to catch fish. Supplementing this meagre protein diet were roots and tubers, insects and snails. The heroics of the mammoth hunt became a thing of the past and life became a gruelling fight for survival.
The close cooperation between human and dogs, by now thoroughly assimilated into human society, continued even though the superbly effective working partnership that had developed in the Upper Palaeolithic was at its best when killing large prey, a practice which by now was rapidly disappearing.
Around 12,000 years BP much smaller dogs made their debut in the fossil record. A team of French archaeologists found the remains of thirty-nine dogs at the Pont d’Ambron rock-shelter in the Dordogne. From an osteometric analysis similar to that carried out at the earlier sites of Goyet and Trou des Nutons in the Ardennes, it was clear that the Pont d’Ambron dogs were considerably smaller. The same
