Grey wolves have more in common with Fido than you might think. A paper published in Evolutionary Applications found that 62 percent of Eurasian grey wolf genomes contain small blocks of domestic dog DNA, revealing centuries of interbreeding that has left an indisputable genetic imprint in the wild wolf gene pool.  

"The fact that wild wolves can cross-breed with dogs is well-documented, but little was previously known about how widespread this phenomenon has been and how it has affected the genetic composition of wild wolf populations,” Malgorzata Pilot of the School of Life Sciences at the University of Lincoln and lead author of the paper explained in a statement.

The team of international scientists came to this conclusion after examining the genomes of domestic dogs and Eurasian gray wolves. Specifically, they looked at a type of genetic variation in DNA sequences called a Single Nucleotide Polymorphism (SNP), which occur when a single nucleotide in an individual's genome differs to those of other members of his or her species.

The results of this analysis show that wolf-dog hybridization has been far more widespread in Eurasia than previously thought, though the extent of this cross-breeding likely varies across regions and time periods. It may be that levels of cross-breeding have remained fairly consistent since the divergence of the two species 11,000 to 35,000 years ago when humans first started domesticating dogs by separating the docile wolf ancestors from their more aggressive pack mates. However, it could also be that hybridization has become more commonplace as wolf numbers decline and dog numbers rise.

And while wild Eurasian wolves, at least for now, remain genetically distinct from domestic dogs, the study does highlight certain ambiguities when it comes to defining what makes a "pure wolf".

"Our research highlighted that some individual wolves which had been identified as 'pure wolves' according to their physical characteristics were actually shown to be of mixed ancestry. On the other hand, two Italian wolves with an unusual, black coat color did not show any genetic signatures of hybridization, except for carrying a dog-derived variant of a gene linked to dark coloration," Pilot said. 

"This suggests that the definition of genetically 'pure' wolves can be ambiguous and identifying admixed individuals can be difficult, implying that management strategies based on removal of suspected hybrids from wolf populations may be inefficient."