An international team of geneticists and archaeologists led by the Francis Crick Institute discovered that dogs' ancestors can be traced back to at least two ancient wolf populations. The findings bring us one step closer to solving the mystery of where dogs first became domesticated, one of the most pressing unanswered questions in human prehistory.
Dogs are thought to have descended from the gray wolf, with domestication taking place at least 15,000 years ago during the Ice Age. However, it is unknown where this occurred and whether it occurred in a single location or in multiple locations.
Previous research using the archaeological record and comparing DNA from dogs and modern wolves did not yield an answer.
The researchers used ancient wolf genomes in their study, which was published in Nature today (June 29), to better understand where the first dogs evolved from wolves. They examined 72 ancient wolf genomes from Europe, Siberia, and North America dating back 100,000 years.
The remains were discovered in previously excavated ancient wolves, and archaeologists from 38 institutions in 16 countries contributed to the study. The remains included a complete, perfectly preserved head from a 32,000-year-old Siberian wolf. The wolves' DNA sequence data was then generated by nine different ancient DNA labs working together.
The researchers discovered that both early and modern dogs are more genetically similar to ancient wolves in Asia than to those in Europe, implying a domestication somewhere in the east.
They did, however, discover evidence that two distinct populations of wolves contributed DNA to dogs. Early dogs from northern Europe, Siberia, and the Americas appear to have descended from a single, eastern source. In addition to the eastern source, early dogs from the Middle East, Africa, and southern Europe appear to have some ancestry from another source related to wolves in the Middle East.
One possible explanation for this dual ancestry is that wolves were domesticated multiple times, with different populations eventually mixing together. Another possibility is that domestication occurred only once, and the dual ancestry is the result of these early dogs mixing with wild wolves. It is currently impossible to tell which of these two scenarios took place.
"Through this project, we have greatly increased the number of sequenced ancient wolf genomes, allowing us to create a detailed picture of wolf ancestry over time, including around the time of dog origins," says Anders Bergström, co-first author and post-doctoral researcher in the Crick's Ancient Genomics lab.
"By attempting to fit the dog into this picture, we discovered that dogs derive ancestry from at least two distinct wolf populations: an eastern source that contributed to all dogs and a separate more western source that contributed to some dogs."
The team is still looking for a close ancient wolf ancestor of dogs, which could reveal more precisely where domestication occurred. They are now concentrating on genomes from locations not included in this study, such as more southern regions.
Because the 72 ancient wolf genomes spanned approximately 30,000 generations, it was possible to construct a timeline of how wolf DNA has changed, tracing natural selection in action.
For example, they discovered that over a 10,000-year period, one gene variant went from being extremely rare to being present in every wolf, and it is still present in all wolves and dogs today. The variant affects IFT88, a gene involved in the development of skull and jaw bones. It is possible that the spread of this variant was influenced by a change in the types of prey available during the Ice Age, giving wolves with a specific head shape an advantage, but the gene could also have other unknown functions in wolves.
"This is the first time scientists have directly tracked natural selection in a large animal over a time scale of 100,000 years, seeing evolution play out in real-time rather than trying to reconstruct it from DNA today," says Pontus Skoglund, senior author and group leader of the Crick's Ancient Genomics lab.
"We discovered several cases where mutations spread to the entire wolf species, which was possible due to the species' high connectivity over long distances. This connectivity may explain why wolves survived the Ice Age while many other large carnivores perished."
"Similar Ice Age whole-genome time series in humans or other animals could provide new information about how evolution occurs."
Reference: DOI: 10.1038/s41586-022-04824-9