by Dogs were the first species that humans domesticated and have been an integral part of human life for thousands of years. Domesticated species are plants and animals that have evolved to live alongside humans and provide almost all of our food as well as numerous other benefits. Dogs provide protection, hunting assistance, companionship, transportation, and even wool for weaving blankets.
Dogs evolved from gray wolves, but scientists debate exactly where, when, and how often dogs were domesticated. Ancient DNA evidence suggests that domestication occurred twice, in eastern and western Eurasia, before the groups eventually mixed. This mixed population was the ancestor of all dogs alive today.
Molecular clock analysis of the DNA of hundreds of modern and ancient dogs suggests that they were domesticated around 20,000 to 22,000 years ago, when large ice sheets covered much of Eurasia and North America. The first dog identified in the archaeological record is a 14,000-year-old puppy found in Bonn-Oberkassel, Germany. However, it can be difficult to tell from the bones whether an animal was an early domestic dog or a wild wolf.
Despite the shared history of dogs and wolves, scientists have long assumed that these two species rarely mated and produced hybrid offspring. As an evolutionary biologist and molecular anthropologist who studies native plants and animals, we wanted to take a fresh look at whether dog-wolf hybridization was really that unusual.
Few crossings in the wild
Dogs are not necessarily descended from modern wolves. Rather, dogs and wolves living today come from a common ancient wolf population that lived alongside woolly mammoths and cave bears.
In most domesticated species, there are often clear, documented patterns of gene flow between animals living alongside humans and their wild counterparts. Where the habitats of wild and domesticated animals overlap, they can interbreed and produce hybrid offspring. In these cases, wild animal genes are inserted into the genetic variation of the domesticated population.
For example, pigs were domesticated in the Middle East over 10,000 years ago. But when early farmers brought them to Europe, they hybridized so frequently with native wild boars that almost all of their Middle Eastern DNA was replaced. Similar patterns can be seen in the endangered wild Anatolian and Cypriot mouflons, whose genomes contain high levels of domestic sheep DNA, according to researchers. It is becoming increasingly common for wild and domestic animals to interbreed and share genetic material over time.
That wolves and dogs would not show this typical pattern is surprising, since they live in overlapping ranges and can interbreed freely.
However, the behavior of dogs and wolves is completely different, as wolves are generally organized in a family pack structure and dogs rely on humans. When hybridization occurs, it typically occurs when human activities—such as habitat invasion and hunting—disrupt pack dynamics, causing female wolves to strike out on their own and mate with male dogs. In the 20th century, some “wolfdog” hybrid types were deliberately bred, but these are considered to be exceptions.
Luna Belle, a resident of the Wolf Sanctuary of Pennsylvania, where both wolves and wolfdogs live. Audrey Lin
Tiny but recognizable wolf ancestry
To investigate how much gene flow between dogs and wolves actually occurred after domestication, we analyzed 2,693 previously published genomes using extensive publicly available datasets.
These included 146 ancient dogs and wolves dating back about 100,000 years. We also looked at 1,872 modern dogs, including Golden Retrievers, Chihuahuas, Malamutes, Basenjis and other well-known breeds, as well as more unusual breeds from around the world like the Caucasian Ovcharka and the Swedish Vallhund.
Finally, we included genomes from around 300 “village dogs”. These are not pets, but rather free-living animals that rely on a close connection with the human environment.
We traced the evolutionary history of all these canids by examining the maternal lineages using their mitochondrial genomes and the paternal lineages using their Y chromosomes. We used highly sensitive computational methods to delve into the nuclear genomes of dogs and wolves – that is, the genetic material contained in the nuclei of their cells.
We found the presence of wild wolf genes in most dog genomes and the presence of dog genes in about half of wild wolf genomes. The mark of the wolf was small, but it was there, in the form of tiny, barely noticeable pieces of continuous wolf DNA in the chromosomes of dogs. About two-thirds of the pedigree dogs in our sample had wolf genes from crosses that occurred on average about 800 generations ago.
While our results showed that larger working dogs – such as sled dogs and large guard dogs that protect livestock – are generally more likely to descend from wolves, the patterns are not universal. Some large breeds like the St. Bernard lack wolf DNA entirely, but the small Chihuahua has detectable wolf ancestry with 0.2% of its genome. Terriers and hounds are typically on the lower end of the spectrum when it comes to wolf genes.
We were surprised to find that every single village dog we tested had pieces of wolf DNA in its genome. Why should that be so? Village dogs are free-living animals that make up about half of all dogs in the world. Their lives can be hard, with short life expectancy and high infant mortality rates. Village dogs are also associated with pathogenic diseases such as rabies and distemper, making them a public health problem.
The sections of wolf DNA we found in the genome of village dogs contained genes related to olfactory receptors more often than predicted by chance. We hypothesize that olfactory abilities influenced by wolf genes may have helped these free-living dogs survive in harsh, volatile environments.
The intertwining of dogs and wolves
Since dogs evolved from wolves, all dog DNA is originally wolf DNA. So when we talk about the little bits of wolf DNA in dog genomes, we’re not referring to the original wolf gene pool floating around for the last 20,000 years, but rather to evidence that dogs and wolves interbred much later.
A wolf-dog hybrid with one parent of each species would carry 50% dog and 50% wolf DNA. If this hybrid then lived and mated with dogs, its offspring would be 25% wolves, and so on until we only see small fragments of wolf DNA.
The situation is similar to that in the human genome: Neanderthals and humans shared a common ancestor about half a million years ago. However, Neanderthals and our species have homo sapiensIn Eurasia, too, they overlapped and interbred only a few thousand generations ago, shortly before the Neanderthals disappeared. Scientists can detect the small bits of Neanderthal DNA in most living humans in the same way we can detect wolf genes in most dogs.
Our study updates the previous assumption that hybridizations between dogs and wolves are rare; Interactions between these two species show visible genetic traces. Hybridization with free-roaming dogs is considered a threat to conservation efforts of endangered wolves, including Iberian, Italian and Himalayan wolves. However, there is also evidence that dog-wolf interbreeding could provide wolves with genetic advantages as they adapt to environments increasingly dominated by humans.
Although dogs evolved as human companions, wolves served as their genetic lifeline. As dogs encountered evolutionary challenges, such as how to survive in harsh climates, forage for food on the streets, or guard livestock, they were apparently able to use wolf ancestry as part of their evolutionary survival equipment.
This article was republished from The Conversation, a nonprofit, independent news organization that brings you facts and trusted analysis to help you understand our complex world. It was written by: Audrey T. Lin, Smithsonian Institution and Logan Kistler, Smithsonian Institution
Read more:
The authors do not work for, advise, own shares in, or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic employment.
