Even Chihuahuas Still Have Some Wolf in Them — Here’s How Some Dogs Still Carry This DNA

All modern-day pooches, from beefy Newfoundlands to scrawny Salukis, are descended from an ancient population of domesticated gray wolves. Despite the 20,000 or so years that have passed since, a new study published in Proceedings of the National Academy of Sciences has concluded that the majority of dog breeds alive today have detectable levels of wolf DNA in their genomes.

These gene signals may contribute to characteristics that have shaped our relationship with dogs over millennia, including personality, sense of smell, and body size. Dogs’ enduring wolf ancestry, wrote the authors of the new work, “has shaped their evolution and conferred unique advantages to their survival in diverse human environments.”

“Modern dogs, especially pet dogs, can seem so removed from wolves, which are often demonized,” said Audrey Lin, a bioinformatician at the American Museum of Natural History and study co-author, in a press release. “But there are some characteristics that may have come from wolves that we greatly value in dogs today and that we choose to keep in their lineage.”

Can 20,000 Years Separate Dogs And Wolves?

Dogs and wolves, despite sharing similar geographical ranges, rarely interbreed. This meant that previous analyses had concluded domesticated dogs were unlikely to harbor much residual wolf DNA, said Lin. But her team’s close analysis suggested that wolf ancestry is embedded in modern-day dogs’ genomes.

“This suggests that dog genomes can ‘tolerate’ wolf DNA up to an unknown level and still remain the dogs we know and love,” Lin added.

Lin’s new study explored the genomes of more than 2,700 dogs and wolves across 20,000 years of history, contained in the National Center for Biotechnology Information and the European Nucleotide Archive. Over two-thirds of modern breed dogs still retain DNA from wolf crossbreeding that occurred 1,000 generations ago. Interestingly, 100 percent of free-roaming village dogs living in and around human settlements carried wolf ancestry.

The highest levels of wolf ancestry were found in samples taken from Czechoslovakian and Saarloos wolfdogs. These high levels are unsurprising, as the breeds were created by purposely crossbreeding German Shepherds with Carpathian and Siberian gray wolves, respectively.

Among dogs without a history of purposeful crossbreeding, samples from two Grand Anglo-Francais Tricolore hounds led the way, with 5.7 percent and 4.7 percent wolf ancestry, respectively. These findings were surprising, as these dogs, the most common hound in modern France, have no recognized history of wolf crossbreeding.

Trends in Wolf DNA

Further, the Grand Anglo-Francais Tricolore had the highest variance of all breeds analyzed, with some other dogs of the same breed containing very low levels of wolf DNA. The two outlying Tricolores contained far more wolf ancestry than even the Tamaskan Dog, which was created by combining various Arctic dog breeds to develop a superficially wolflike appearance. The Tricolore, Tamaskan, and the Shiloh shepherd were the only breeds to contain more than 2 percent wolf ancestry.

The study also uncovered broader trends. Wolf DNA levels were higher in larger dogs and in those bred for sled work. The team found the lowest average levels of wolf ancestry in terriers, gun dogs, and scent hounds. Larger guardian dogs generally had low wolf ancestry, although a small number of individuals with high ancestry levels skewed their average.

The minuscule chihuahua, for its part, had on average 0.2 percent wolf ancestry.

What Words Make A Dog More Wolf-Like?

The team also analyzed which words were most and least used to describe high- and low-wolf dog breeds. Dogs with high wolf ancestry were likely to be described as “suspicious of strangers,” “alert”, “loyal”, and “territorial.” Low-wolf-ancestry breeds, in contrast, were most often described as “friendly,” “eager to please,” “easy to train,” “courageous,” “lively,” and “affectionate.” Any links between these behaviors and wolf DNA are purely correlational. The team says more study is needed to establish a causal link.

The team identified two specific instances where certain dog breeds have benefited from wolf ancestry. Tibetan mastiffs have a high level of a gene derived from wolves that enables them to endure low oxygen levels in their high-altitude territory. Some village dogs had olfactory receptor genes with a high level of wolf ancestry. These free-roaming dogs need to be able to sniff out food to survive.

“Dogs are our buddies, but apparently wolves have been a big part of shaping them into the companions we know and love today,” said Logan Kistler, study co-author and curator at the National Museum of Natural History, in the press release.

Read More: Why There’s the Leader of the Wolf Pack

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