One the strange ironies about dogs is that we have set up a system in which populations are maintained without regular influxes of new blood. However, at no point in the evolutionary history was this ever the case.
Some dog fanciers maintain breeds as if they were distinct species, and in some breeds, one can find lore that they are derived from sort of wild canid that has nothing to do with wolves or the rest of dogdom. Chihuahuas are supposedly domestic variants of the fennec fox. The Japanese chin was said to be distinct species that belonged to its own genus.
But no matter how you slice it, domestic dogs are all one species, and what is even more important, the more we have found out about the genome and that of their closest relatives, the harder it becomes to think of them as a distinct species from the wolf.
And if that weren’t such a revelation, it really gets more bizarre when we have no learned that wolves, golden jackals, and coyotes are not the cut-and-dry species we assumed them to be. In Eastern Canada and the Northeastern US and Midwestern US, we have discovered that wolves and coyotes have hybridized a whole lot more than we realized. We have also found evidence that golden jackals and wolves have hybridized in Bulgaria. Both coyotes and golden jackals can cross with wolves or domestic dogs and produce fertile offspring.
To make things more complicated, it turns out that wolves and golden jackals have continued to exchange genes since the two species separated. A recent genome-wide study of modern dogs, wolves, and golden jackals revealed that Eurasian wolves and golden jackals continued to mate with each other after their initial separation. The authors found substantial gene flow between golden jackals and Israeli wolves, as well as the ancestral population to all wolves and domestic dogs.
Most North Americans are aware of the taxonomic controversies involving coyote and wolf hybrid populations, including the red wolf and the proposed “Eastern wolf” species, but it turns out that this problem also exists in the Old World.
There is now a debate as to whether certain sub-Saharan and North African golden jackals are golden jackals or wolves. A few years ago, there were several studies that suggested that the mitochondrial DNA of certain African golden jackals were actually those of a primitive wolf lineage. There is still some debate as to whether these animals are wolves or jackals, and some of the proposed wolves have been found to hybridize with golden jackals in Senegal.
In utter ignorance of the natural history of wild Canis, domestic dog fanciers have spent the past century to century and half splitting up gene pools under the delusion that this somehow preserves them. Never mind that for most of their suggested 2 or 3 million years on the planet, wild wolves have continued to exchange genes with their closest relatives. When species hybridize, it was always thought that this would be a negative, but in truth, hybridization can be source of genetic rescue. In the case of Eastern coyotes, crossing with wolves can introduce new genes for more powerful jaws and larger size, which make them better predators of deer. It can also introduce new MHC haplotypes, which can provide the animal with enhanced immunity to disease.
One way of looking at golden jackals and coyotes is they are actually themselves primitive wolves. This might sound a bit heretical, but if you were to go back into time and find the ancestor of all wolves, golden jackals, and coyotes, it would look more less like a golden jackal or coyote. I would argue that these animals represent a sort of generalized template from which larger, more specialized forms can evolve. One of the problems in sorting out wolf, coyote, and jackal lineages from the fossil record is that at various times through their history on the planet, different lineages have evolved larger wolf-like sizes or have produced coyote or jackal-like forms to fit the niche in question.
A recent comparison of golden jackals, African golden jackals that might be wolves (Canis lupus lupaster or Canis lupaster), black-backed jackals, modern wolves, and the extinct Canis etruscus and Canis arnensis revealed that those the proposed African wolves had skull morphologies that were closer to known golden jackals and black-backed jackals. If these lupaster canids are actually wolves and not jackals, then we would have never been able to guess their identity upon morphology alone.
So while the dog fancy has been splitting hairs and arbitrarily dividing up gene pools, science has revealed that the wild dogs haven’t been doing the same.
Canis is not a closed registry.
Even the boundaries between wolves and golden jackals and between wolves and coyotes are blurry, and of course, this leaves out the rather significant gene flow that has occurred between domestic dogs and wild wolves. Black wolves and wolves with dewclaws on the hind legs are the result of dogs and wolves mating “in the wild.”
Science has found all of these wonderful things out, but the dog fancy remains stuck in another era.
Maybe someday it will move beyond the closed registry system and instead of offering up the bromide of “breed preservation,” it will adopt a system of “breed management,” which strives to maintain genetic diversity within a breed and allows regular influxes of outside blood.
That is what nature has allowed with the wild Canis.
That is the actual story of the animals of this genus. It is not one of one lineage remaining pure for millions or even thousands of years.
It is about significant hybridization.
And Canis is not the only genus with this hybridization issue. Ducks in the genus Anas hybridize quite a bit, and it is well-known that many species of whales and dolphins hybridize with their close kin as well. All of these animals are fairly mobile organisms, and their mobility is likely why they retain so much interfertility. They simply cannot be reproductively isolated from their closest relatives long enough for them to lose chemical interfertility.
It is not something that should be thought of as an evil. Instead, it’s actually a major strength. It is one our own species utilized when we exchanged genes with the Neanderthals and Denisovan people, and if there were another human species alive today, we would likely be able to cross with it.
But because we are so alone in this world, it is difficult for us to understand the concept of a species complex. We are the only humans left.
But dogs and wolves are not the last of their kind.
The gene flow between wild and domestic and among the these three species of Canis is something we have difficulty imagining.
But it is the story of dogkind.