Over the course of thousands of years, humans have carefully and selectively bred domestic dogs to produce a massive and diverse spectrum of animals. It's incredible to consider that the tiny Chihuahua, the massive Saint Bernard, and the wolf-like Malamute are all members of one species. The diversity of dogs, combined with recent trends of deliberately crossing dogs with wolves and other close relatives, has given rise to the idea that some pet dogs may in fact be part fox. The idea is certainly intriguing, but is it true? Can dogs really breed with foxes?
The short answer is no. In order to breed together (and especially to produce fertile offspring), two species have to be very closely related and need to share the same number of chromosomes and a similar genetic pattern. Although dogs and foxes are members of the same family (Canidae), they actually parted from one another some ten million years ago and took different evolutionary paths. As a result, dogs and foxes have radically different DNA and a completely different number of chromosomes. Additionally, behavioral and biological differences between dogs and foxes make it unlikely that a dog and a fox would naturally be able or inclined to mate.
Dogs only recently diverged from some of their closest wild kin, so they can still breed freely with some non-domestic species. For example, dogs are actually considered to be a subspecies of grey wolf, and can easily interbreed with them. They share the same number of chromosomes (78) and the same basic genetic pattern. Domestic dogs can also interbreed with several other 78-chromosome wild canines, including the coyote, dhole, and dingo. These mixes actually aren't entirely uncommon and can happen either as a result of deliberate cross-breeding or when feral and stray dogs mate with their wild kin.
However, for foxes, which are the domestic dogs' more distant relatives, interbreeding is much, much less likely. According to a report by the World Conservation Union, foxes vary tremendously in the number of chromosomes they carry, depending on the species. The bat-eared fox, which is most closely related to the dog, has 72 chromosomes, and it would be very unlikely that they could mate and produce fertile young. The grey fox has 66 chromosomes, while the fennec fox has 64 and he Bengal fox has 60. Some of the most charismatic and well-known fox species have even fewer chromosomes, with kit foxes sporting just 50 chromosomes and red foxes carriying only 34. The odds of successfully cross-breeding go down tremendously as the gap between the number of chromosomes widens.
Finally, while differences in size and behavior have never stopped domestic dogs from sometimes producing unlikely young (like Labrador-dachshund mixes), it's not likely that dogs would naturally mate with foxes. Foxes tend to be extremely small compared to average dogs, and, unlike dogs, foxes are very solitary animals with very different mating behaviors. Even if there was some possibility that they could interbreed (and so far, there is little evidence of that possibility), dogs and foxes would not generally choose to mate with one another.
Ultimately, while the idea of a dog-fox hybrid is intriguing, these cross-species mixes are probably impossible. Still, there are many breeds of dog with the vulpine traits that some owners might be inclined to seek, such as the Pomeranian, the shiba inu, and the Cardigan Welsh corgi. Researchers have also bred foxes that behaviorally and physically resemble dogs, despite being full-blooded red foxes. While true fox-dogs may remain only a fantasy, there are many ways for fans of foxes and dogs to get the best of both worlds.