A dog (Canis lupus familiaris) and a wolf (canis lupus) can interbreed to create fertile offspring, but such occurrences are far less common than in domestic and wild populations of other species. In a recent study, researchers from the American Museum of Natural History, the Smithsonian National Museum of Natural History, and the University of California, Davis, combined localized ancestry estimation with phylogenetic analysis of the genomes of 2,693 ancient and modern dogs and wolves. They discovered that 64.1% of contemporary purebred dogs possess wolf ancestry in their nuclear genomes, stemming from admixture that occurred nearly 1,000 generations ago, while all analyzed free-ranging dog genomes showed signs of ancient wolf ancestry.

“Modern dogs, especially those kept as pets, seem quite distant from the often vilified wolves,” states Dr. Audrey Lin, a postdoctoral fellow at the American Museum of Natural History.

“However, certain wolf-derived traits are highly valued in our current dogs, and we have intentionally preserved them in this lineage.”

“While this research focuses on dogs, it reveals much about their wild relatives, the wolves.”

Dogs evolved from a gray wolf population that faced extinction due to human influence during the late Pleistocene, approximately 20,000 years ago.

Though wolves and dogs inhabit overlapping areas and produce fertile offspring, instances of interbreeding are infrequent.

Aside from rare cases of intentional interbreeding, there is limited evidence of genetic exchange between the two groups following dog domestication, which separated their gene pools.

“Prior to this study, prevailing theories posited that for a dog to be classified as such, it would need to have minimal or no wolf DNA,” remarked Dr. Lin.

“Yet, upon examining the modern dog genome closely, we found wolf DNA present.”

“This indicates that the dog’s genome can incorporate wolf DNA to varying extents without losing its identity as a dog.”

The researchers scrutinized historical gene flow between dogs and wolves utilizing 2,693 publicly accessible genomes from wolves, purebred dogs, village dogs, and other canids from the late Pleistocene to the present, sourced from the National Center for Biotechnology Information and the European Nucleotide Archive.

The findings revealed that 64.1% of breed dogs possess wolf ancestry in their nuclear genomes, a result of crossbreeding occurring about 1,000 generations ago.

Moreover, all genomes from village dogs (free-ranging canines residing near human settlements) displayed detectable wolf ancestry.

The Czechoslovakian wolfdog and Saarlos wolfdog, which were purposefully crossbred with wolves, exhibited the highest levels of wolf ancestry, ranging from 23% to 40% of their genomes.

The breeds considered most “wolf-like” include the Great Anglo-French Tricolor Hound (4.7% to 5.7% wolf ancestry) and the Shiloh Shepherd (2.7% wolf ancestry).

The Shiloh Shepherd is the result of breeding efforts that included wolf-dog hybrids aimed at producing healthier, family-friendly sheepdogs in the U.S., while the origins of the significant wolf ancestry in the Great Anglo-French Tricolor Hound (the prevalent modern hunting dog in France) remain enigmatic.

The Tamaskan is another “wolf-like” breed that emerged in the UK during the 1980s by selectively breeding huskies, malamutes, and others to achieve a wolf-like appearance, containing roughly 3.7% wolf ancestry.

Researchers identified several patterns within the data. Larger dogs and those bred for specific tasks, such as arctic sled dogs, “pariah” breeds, and hunting dogs, exhibited higher levels of wolf ancestry.

Terriers, gundogs, and scent hounds typically have the least wolf ancestry on average.

While some large guardian breeds have wolf ancestry, others, such as the Neapolitan Mastiff, Bullmastiff, and St. Bernard, showed no signs of wolf ancestry.

Interestingly, wolf ancestry was also detected in a variety of dog breeds, including the miniature Chihuahua, which has around 0.2% wolf ancestry.

“This shouldn’t surprise anyone who owns a Chihuahua,” Dr. Lin noted.

“What we’ve discovered is that this is actually common. Most dogs have a hint of ‘wolfishness’ in them.”

The authors also analyzed the frequency with which personality traits were assigned to breeds labeled with high versus low levels of wolf ancestry by Kennel Clubs.

Breeds with lower wolf ancestry were often described as “friendly,” followed by terms like “eager to please,” “easy to train,” “courageous,” “active,” and “affectionate.”

Conversely, dogs exhibiting higher wolf ancestry were more frequently characterized as “independent,” “dignified,” “alert,” “loyal,” “discreet,” “territorial,” and “suspicious of strangers.”

Traits such as “smart,” “obedient,” “good with kids,” “dedicated,” “calm,” and “cheerful” appeared with relative consistency across both groups of dogs.

The researchers clarified that these traits reflect a biased assessment of behavior and that it’s uncertain whether wolf genes directly influence these characteristics, though their findings lay the groundwork for future explorations in canine behavioral science.

Additionally, significant adaptations inherited from wolves were uncovered. For instance, the wolf ancestry in village dogs enhances their olfactory receptor genes, crucial for locating human food waste, and distributions of Tibetan wolf-like genes assist Tibetan mastiffs in surviving low-oxygen conditions on the Tibetan Plateau and Himalayas.

“Dogs are our companions, but it appears that wolves significantly influenced their evolution into the beloved partners we cherish today,” commented Dr. Logan Kistler from the National Museum of Natural History.

“Throughout history, dogs have tackled numerous evolutionary challenges that arise from living alongside humans, such as thriving at high altitudes, foraging for food around villages, and safeguarding their packs. They seem to leverage wolf genes as part of their adaptive toolkit for an ongoing evolutionary success story.”

For more details, check the findings published this week in Proceedings of the National Academy of Sciences.

_____

Audrey T. Lin et al. 2025. The legacy of genetic intertwining with wolves has shaped the modern dog. PNAS 122 (48): e2421768122; doi: 10.1073/pnas.2421768122