Ancient wolf genome reveals an early divergence of domestic dog ancestors

Dogs' special relationship to humans may go back 27,000 to 40,000 years, according to genomic analysis of an ancient Taimyr wolf bone. Earlier genome-based estimates have suggested that the ancestors of modern-day dogs diverged from wolves no more than 16,000 years ago, after the last Ice Age. Dogs' special relationship to humans may go back 27,000 to 40,000 years, according to genomic analysis of an ancient Taimyr wolf bone reported in the Cell Press journal Current Biology on May 21. Earlier genome-based estimates have suggested that the ancestors of modern-day dogs diverged from wolves no more than 16,000 years ago, after the last Ice Age.

The genome from this ancient specimen, which has been radiocarbon dated to 35,000 years ago, reveals that the Taimyr wolf represents the most recent common ancestor of modern wolves and dogs.

"Dogs may have been domesticated much earlier than is generally believed," says Love Dalén of the Swedish Museum of Natural History. "The only other explanation is that there was a major divergence between two wolf populations at that time, and one of these populations subsequently gave rise to all modern wolves." Dalén considers this second explanation less likely, since it would require that the second wolf population subsequently became extinct in the wild.

"It is [still] possible that a population of wolves remained relatively untamed but tracked human groups to a large degree, for a long time," adds first author of the study Pontus Skoglund of Harvard Medical School and the Broad Institute.

The researchers made these discoveries based on a small piece of bone picked up during an expedition to the Taimyr Peninsula in Siberia. Initially, they didn't realize the bone fragment came from a wolf at all; this was only determined using a genetic test back in the laboratory. But wolves are common on the Taimyr Peninsula, and the bone could have easily belonged to a modern-day wolf. On a hunch, the researchers decided to radiocarbon date the bone anyway. It was only then that they realized what they had: a 35,000-year-old bone from an ancient Taimyr wolf.

The DNA evidence also shows that modern-day Siberian Huskies and Greenland sled dogs share an unusually large number of genes with the ancient Taimyr wolf.

"The power of DNA can provide direct evidence that a Siberian Husky you see walking down the street shares ancestry with a wolf that roamed Northern Siberia 35,000 years ago," Skoglund says. To put that in perspective, "this wolf lived just a few thousand years after Neandertals disappeared from Europe and modern humans started populating Europe and Asia."

Citation

Skoglund et al. 2015. Ancient wolf genome reveals an early divergence of domestic dog ancestors and admixture into high-latitude breeds. Current Biology, 2015 DOI: 10.1016/j.cub.2015.04.019

The Goyet and Eliseevichi skulls were wolves not dogs, and a thought on the wolf-dog transition

The dates for dog domestication have been controversial. Some evidence (the Goyet cave fossils) pointed to the Pleistocene with the skulls suggesting dogs were transitioning from wolves to dogs, while other evidence suggested wolves transitioned to dogs when humans were hunter-gatherers, or during the Neolithic, when humans began living in more permanent settlements and engage in agriculture. Recently discovered Paleolithic fossil skulls, Goyet dated 31,680 +/− 250 YBP in the Czech Republic and Eliseevich 1 MAE (13,905 +/− 55 YBP) from the Bryansk Region in the central Russian Plain, were identified as dogs, establishing the date of dog domestication in the Paleolithic contemporaneous with human hunter-gatherers.

In a new paper Drake et al. (2015) use 3D geometric morphometric analyses to compare the cranial morphology of Goyet and Eliseevichi MAE to that of ancient and modern dogs and wolves. They find the Paleolithic canids are definitively wolves and not dogs. When compared to wolf-like breeds the skulls from Goyet and Eliseevichi MAE lack a cranial flexion and the dorsal surface of their muzzles do not have a concavity near the orbits. Morphologically, the fossils resemble wolves and no longer support the establishment of dog domestication in the Paleolithic.

The analysis in Drake et al. suggest previous measurement methodologies do not provide the resolution needed for distinguishing dogs from wolves and that 3D landmark-based geometric morphometric methods are better suited for the job. Geometric morphometric methods preserve size and shape information and allow for the inclusion of shape variation that cannot be gathered via calipers measurements.

Mitochondrial genomes revealed that Goyet, and other Paleolithic wolves, form the sister to all ancient and modern dogs. The Eliseevichi MAE, was not recovered in a clade with modern dogs but was genetically affiliated with modern wolves from Finland and Russia. The data from Drake et al is in accordance with the genetic evidence and they conclude that the Goyet and Eliseevichi MAE skulls lie within the wolf morphospace, together with the Paleolithic Alaskan wolves and Trou Balleux from Belgium. Drake et al. suggest a reassessment of the classification of the other fossil canids such as the Altai specimen (dated about 33,000 YBP) using 3D landmark-based geometric morphometric methods combined with genetic data, is needed to address the origin of domestication.

The Drake paper’s new classification of Goyet and Eliseevichi MAE as wolves, also suggests a reestablishment of the timing of dog domestication in the Neolithic. If shown to be correct it supports the Coppinger and Coppinger hypothesis that dog domestication occurred in the Neolithic when wolves began to scavenge near human settlements. Their hypothesis suggested human settlements provided a new niche because of the permanent supply of waste food and when combined with the Belyaev's experiment suggested wolf domestication could occur quickly. The establishment of permanent settlements in the Neolithic would have created an environment where sustained selection for tameness could exist for many generations thus setting the stage for dog domestication.

It seems unlikely this is the final word on the date of dog domestication and it simply shows that these skulls were wolves. But, they were wolves associated with archeological sites, not randomly found fossils. Thus the possibility that they were in some way associated with humans suggests there is more to the story. Pre-adaptive behaviors in wolves likely preceded domestication events. Yes, human settlements would have provided a continuous supply of garbage that could be scavenged. But prior to human settlements there was also a likely supply of wasted food that could have been exploited by wolves, paleo-dogs, and other scavengers – leftovers from megafauna kills. Large mammals killed during a hunt were unlikely to be completely consumed by the human hunters. 

Scavenging these large patches of waste nutrients would have brought humans and wolves into close contact – long before humans were living in Neolithic settlements. This scenario is more in line with the genetic results of Wang et al. (2013) suggesting parallel evolution between humans and dogs. The interesting part of this story is not necessarily the date when dogs and wolves diverged, but the events leading up to that date and the prior relationship between the dog’s ancestor and early humans. This was a relationship that likely changed the evolutionary trajectory of both the canine and the primate.

Citations

Drake AG,Coquerelle M, Colombeau G. 2015. 3D morphometric analysis of fossil canid skulls contradicts the suggested domestication of dogs during the late Paleolithic. Scientific Reports 2015/02/05/online. http://dx.doi.org/10.1038/srep08299

Wang GD, et al. (2013). The genomics of selection in dogs and the parallel evolution between dogs and humans. Nature communications, 4, 1860.