cave in the northern foothills of the Pyrenees and at the open-air site of Le Closeau in an old channel of the River Seine.
The authors of the exhaustive paper summarising this body of work confidently concluded that they were dealing with the remains of dogs and not wolves. In France at least, and also in Spain, dogs were clearly changing. In Russia, however, at around the same time, wolf-dogs were still very large. Whether this was a result of separate wolf domestications in the two regions or for some other reason, it was impossible to say. One firm but rather grisly conclusion, drawn from cut-marks on the bones of the Pont d’Ambron dogs, was that they had been butchered and, presumably, cooked and eaten.
As well as the issue of timing, the identification of the geographical location of the wolf–dog transition has absorbed many researchers and continues to do so. The first scenario to be proposed, by a group from the University of Konstanz in Switzerland led by Peter Savolainen, was that the major ‘domestication’ event happened only once, in East Asia.2 This was the conclusion of an mDNA study of 654 dogs from different regions of the world where the focus was on the diversity of sequences. The perfectly sensible rationale was that the highest diversity, that is the highest number of different mDNA lineages, would be found in the places where dogs had been around the longest and had the most time to accumulate new mutations, rather like the islanders in our metaphorical example. Savolainen’s team found mDNA sequence diversity was highest in south-east Asia and located the first ‘domestication’ to the region. This was a very controversial conclusion at the time, and it would be another decade before the debate was settled, although it still rumbles on in some quarters.3
In order to make progress on the vexing issues of timing and location, scientists turned to the DNA that had, incredibly (a word I do not use lightly), survived in fossils. Robert Wayne, who headed the Los Angeles lab, was one of the eclectic bunch of scientists who dared to think, against all reason and common sense, that DNA might survive in fossils. As there was no academic tradition of ancient DNA science and this was an entirely new field, the early pioneers came from all sorts of backgrounds. Svante Pääbo, for example, who went on to sequence Neanderthal DNA, was originally an immunologist with an interest in Egyptology that led him to attempt to extract DNA from mummies in 1985. Ed Golenberg, who claimed in a 1990 Nature article that he had extracted DNA from a 17-million-year-old magnolia leaf, was a botanist. Scott Woodward, in a paper published by Science in 1994, reported DNA extraction from a fossil dinosaur Tyrannosaurus rex from the Cretaceous period entombed in a block of coal. Woodward was a geneticist from Brigham Young University in Utah who went on to run a large genetic genealogy project for the Mormon Church. My own background was in medical genetics, specifically the causes of inherited bone disease. In 1989 my colleagues and I reported the first recovery of ancient bone DNA in Nature.
We met regularly to feel our way in this exciting but tricky field where extravagant claims could be accepted for publication by the very best journals – and, more often than not, be rapidly dismissed. Robert Wayne was a regular attendee at these meetings. He is an evolutionary zoologist with an interest, at the time, in the hybridisation of wolves and coyotes where their ranges overlapped. Robert has gone on to become the pre-eminent scientist in dog genetics, first with work on fossil DNA and then with extensive analyses of the genetic variation in living dog breeds. Much of what we know about the genetics of dog evolution comes from Wayne’s lab in Los Angeles. I was slightly surprised to discover that Wayne doesn’t own a dog, but he does have a cat.
Once the field settled down in the years following the initial papers on ancient DNA recovery, a number of labs began to report its successful extraction from fossil wolves and unambiguous dogs, sometimes of great antiquity.
The field advanced in fits and starts, at first with the publication of single cases, then a few related finds and eventually, in 2013, a large series that seems, for now, to have settled the question of the origin of the wolf–dog transition in favour of Europe between 19,000 and 32,000 years ago.4
In the first decade of this century, the protocols for recovering ancient DNA improved a great deal and it became realistic routinely to obtain long sequences from old bone. Once again mitochondrial DNA was the target, for the very good reason that there are far more copies in a cell compared to nuclear DNA. If you are working at the limits, as you always are with ancient DNA, you want to make things as easy for yourself as possible.
DNA sequencing technology had also advanced to a point where it became practicable to sequence all 16,727 bases of the canid mitochondrial genome from fossils. Analysing the complete sequence avoided the potential bias of restricting the analysis to the shorter ‘control region’ used in the earlier papers by Wayne and Vilà and by Savolainen. The large 2013 study used more or less complete mitochondrial sequences of eighteen fossil ‘canids’ along with a large collection of modern dog breeds. Although not every specimen yielded all base pairs of sequences, it was enough to place them accurately on the evolutionary tree. Nuclear DNA, conversely, was too badly preserved to be of much use.
The resulting tree, or phylogram, to use the proper name, again recognised the four main branches (I–IV in the figure here) of modern dog breeds initially published by Wayne and Vilà. The results were fascinating. The fossil dogs on three of the four branches (I, III, IV) of the tree are closely related to modern breeds while the rare fourth, mainly Scandinavian, branch (II) is closest to modern wolves from Sweden and Ukraine. One possible explanation is that dogs on this branch, which include the Norwegian Elkhound and the Jämthund, acquired their mitochondrial DNA from wild wolves in the recent past, after the advent of agriculture.
While all of the ancient dog lineages have survived to the present day, that is not the case for the fossil wolves. Many of these lineages are now extinct or have simply not been picked up in living wolves yet, though the likelihood of that diminishes as more and more modern wolves are sequenced.
There is a wealth of fascinating detail in the 2013 paper by Olaf Thalmann, which I encourage you contemplate at your leisure from the original publication.5 I do, however, want to mention one particularly surprising finding – about dogs in America. Only two fossil dogs were sequenced, one from Argentina and the other from Illinois, USA. From these mitochondrial sequences these dogs were clearly both related to branch I European dogs, though the ages of the fossils (1,000 and 8,500 years BP respectively) mean that they must have arrived well before the first European settlement in the fifteenth century. These dogs accompanied the indigenous Native Americans who had arrived earlier from Asia. None, however, had mitochondrial DNA remotely like that from American wolves. This has to mean that Native American dogs were ultimately descended from European and not American wolves.
There was another surprise in store. Breeds thought to have been descended from indigenous ‘Pre-Columbian’ dogs, like the Chihuahua and Mexican Hairless, also had an exclusively European mitochondrial heritage. Although sample numbers are quite low, it does look as if the indigenous Native American mitochondrial lineages were another casualty of European settlement.
As the dust settles on the controversies still hovering over the timing and location of the transition from wolf to dog, one thing is certain. It all began a very long time ago.
7
Though hardly fixing the dawn of the transition between wolf and dog with any degree of precision, the genetic dates are embedded in the bounds of what we call the Upper Palaeolithic – the last of the three phases of the Old Stone Age.
The origin of this classification, which is still used today, can be traced to John Lubbock, 1st Baron Avebury. A banker by profession,
