An international group of geneticists and archaeologists has discovered that dogs’ ancestry can be traced back to at least two populations of ancient wolves. The work brings them one step closer to unraveling the mystery of where dogs were domesticated, one of the biggest unanswered questions about human prehistory.
Dogs are known to come from the gray wolf, and this domestication took place during the Ice Age, at least 15,000 years ago. But where this happened, and whether it happened in a single location or multiple places, is still unknown.
Previous studies using archaeological finds and comparing the DNA of dogs and modern wolves have not found the answer.
In their study, published today in Nature, the researchers, including University of Exeter Professor Alan Outram, turned to ancient wolf genomes to better understand where the first dogs evolved from wolves. They analyzed 72 ancient wolf genomes spanning the past 100,000 years, from Europe, Siberia and North America.
The remains came from previously excavated ancient wolves, with archaeologists from 38 institutions in 16 different countries contributing to the study. The remains include a complete, perfectly preserved head of a Siberian wolf that lived 32,000 years ago. Nine different ancient DNA labs then teamed up to generate DNA sequence data from the wolves.
By analyzing the genomes, the researchers found that both early and modern dogs are genetically more similar to ancient wolves in Asia than those in Europe, suggesting a domestication somewhere in the East.
However, they also found evidence that two separate populations of wolves contributed DNA to dogs. Early dogs from Northeastern Europe, Siberia and America appear to have a single, shared origin from the eastern source. But early dogs from the Middle East, Africa, and southern Europe, in addition to the eastern source, appear to have an ancestor from another source associated with wolves in the Middle East.
One possible explanation for this dual ancestry is that wolves were domesticated more than once, with the different populations then mixing. Another possibility is that domestication occurred only once, and that the dual ancestry is due to the fact that these early dogs subsequently mixed with wild wolves. Which of these two scenarios has occurred is currently not possible.
Anders Bergström, co-first author and postdoctoral researcher in the Ancient Genomics lab at the Frances Crick Institute, says: “Through this project, we have greatly increased the number of ancient wolf genomes sequenced, allowing us to create a detailed picture of wolves ancestry in over time, including around the time of the dog’s origin.”
“By trying to place the dog piece in this photo, we found that dogs have ancestry from at least two separate wolf populations — an eastern source contributing to all dogs and a separate, more western source contributing to some dogs.”
The team continues the hunt for a close, ancient canine wolf ancestor, which could more accurately reveal where domestication most likely occurred. They are now targeting genomes from other locations not included in this study, including more southern regions.
Since the 72 ancient wolf genomes spanned about 30,000 generations, it was possible to look back and build a timeline of how wolf DNA has changed, following natural selection in action.
For example, they noted that over a period of about 10,000 years, one gene variant has become very rare in every wolf, and is still present in all wolves and dogs today. The variant affects a gene, IFT88, which is involved in the development of bones in the skull and jaw. It is possible that the spread of this variant was caused by a change in the types of prey available during the Ice Age, which gave wolves with a certain head shape an advantage, but the gene could also have other unknown functions in wolves.
Pontus Skoglund, senior author and group leader of the Ancient Genomics lab at the Crick, says: “This is the first time scientists have directly monitored natural selection in a large animal over a 100,000-year timescale, with evolution taking place in real life. time instead of trying to reconstruct it from DNA today.”
“We found several cases where mutations spread to the entire wolf species, which was possible because the species were highly connected over great distances. This connectivity may be one reason why wolves survived the Ice Age, while many other large carnivores disappeared.”
“Comparable whole-genome time series from the Ice Age, in humans or other animals, could provide new information about how evolution occurs.”
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