How Humans and Dogs Evolved Together

By at least 14,000 years ago, dogs had fully entered into a relationship with humans and earned their place by the campfires of the many hunter-gatherer societies that existed at this time. They were already distinct from gray wolves in appearance, and were also most likely in temperament as well. Most of the changes that these Paleolithic dogs had undergone were to the benefit of humans, but in the story of domestication, we may often take too much credit, as dogs have shaped ours in many ways just as we have shaped them.

It is very well accepted that dogs descended from gray wolves, and there is no evidence of any other canines being involved. The gray wolves alive today are not the direct ancestors of dogs, and they actually descended from a population that is thought to have gone extinct towards the end of the Ice Age. Genetic studies show that this divergence took place around 40,000 years ago, which means this is the highest boundary for when dogs could have been domesticated.

However, the first dogs probably appeared much later than this, as actual dog specimens being found in human settlements tend to be dated later. All this shows is when they split from gray wolves. After this date, there are several remains of canines proposed to be domestic dogs found around Europe and Western Asia. One of the oldest, being found at a cave in Belgium, dated to 36,000 years ago. However, its placement as a true domesticated dog is controversial.

It is difficult to pin down exactly when dogs were domesticated because populations of animals can very quickly evolve tiny differences in appearance within species to help them survive in a slightly different environment. This makes it difficult to know if a specimen is a domesticated dog or just a now-extinct population of gray wolf that looks slightly different. There is no standard to judge how much the dogs have changed.

What makes this even harder is that 10,000 to 60,000 years ago, wolf populations did seem to be more diverse than they are now. In fact, there are identified populations of wolves that existed throughout the northern hemisphere during the Ice Age that were slightly larger and had broader and shorter snouts, adaptations that would have helped them tackle larger prey. These were the Beringian wolf and, in Europe, the megafauna wolf.

Barring a few exceptions, most wolves today are generalists and will eat both large and small prey. But these wolves specialized in hunting the large prey that was more common around this time, like horses, bison, elk, and maybe the now extinct giant deer, Megaloceros.

From around 15,000 to 13,000 years ago, several specimens have been found around Western Europe that scientists have confidently identified as true domesticated dogs, offering the lower boundary for when this could have happened. One of the most famous being the Oberkassel specimen found in Germany.

Surely after these dates, dogs could be found throughout Eurasia. However, it is highly likely that all the dog breeds are most likely descendants of two domestication events. The second domestication occurred in Asia 12,000 years ago and is ancestral for the Asian dog breeds we have today.

Exactly how or why dogs were initially domesticated is uncertain and will probably always be a bit of a mystery as it is something that is very hard to find evidence for. And so, the conversation rarely exceeds speculation.

But dog domestication was most likely not a conscious effort by humans—at least in the initial stages. This is in contrast to, say, livestock animals, which were most likely captured by humans and purposefully domesticated. For humans already ate these creatures, and it is not too much of a jump to start breeding them for food instead of hunting them. Wolves are the only large carnivores that humans have ever domesticated, and pre-domestication interactions with humans were probably often violent. It is hard to believe that early humans were able to foresee all the useful ways in which dogs could be used if they were tamed. Dogs and humans probably had populations that became closer and more intertwined over time, and the domestication was most likely not intentional. They may have been drawn to the human camps by the smell of food being cooked or scraps that had been thrown out. The dogs may have remembered these areas as places to get food, and the hunter-gatherers may have tolerated the less aggressive ones as they were better at spotting the approach of outsiders. These early interactions would have paved the way for future domestication. Rather counter-intuitively, it may have been inevitable that the first amenable animals would have been carnivores, as they are less nervous about approaching other species and being around humans. It is even possible that dogs may have served as an inspiration behind the domestication of later animals.

When dogs began contact with humans, they were thrust into a co-evolutionary journey. As change done to such an extent that many of the ways they socialize are more similar to us than with our closest living relatives. Dogs are very skillful at reacting to human communication cues. For example, they can reliably respond to pointing gestures, while chimpanzees perform poorly with responding to certain human hand gestures without training. This was not a one-sided development; the ease with which humans and dogs can cooperate is due to humans changing too. Scientists have found that interactions between dogs and humans led to an increase in oxytocin levels—a social reward chemical that is associated with bonding and social relationships. There was a raise in levels with both the human and dog participants, but when the experiments tested on hand raised wolves instead of dogs, there was no substantial chemical response in the person showing that humans evolved in this relationship as well. Together, we have taken one another's social attachment systems to create a powerful interspecies bonding mechanism. Dogs did not just co-evolve but convergently evolved with humans as well. When humans started to shift from hunter-gatherer societies to once dominated by agriculture, they evolved to become better at digesting the starchy foods like wheat or rice that would become a significantly larger part of the diet now. Specifically, humans have genes that create amylase in saliva, the enzyme that breaks down starch, beginning the digestion process in the mouth. Since the invention of Agriculture these genes have been copied numerous amounts of times to produce more amylase in response to these selective pressures. What's interesting is that dogs seem to have undergone a similar process with the duplication of a gene called AMY2B. Gray wolves and dingos have two copies of the gene; animals that are primarily carnivorous and probably more similar to early domesticated dogs. Modern-day dogs, on the other hand, have developed many more copies of these genes, making them functionally omnivorous and able to eat starchy foods. As humans traveled throughout the world experiencing vastly contrasting climates and environments, their canine companions...

Also had to endure and adapt to these conditions. Huskies are descendants of sled dogs that were bred by the Chukchi, the indigenous people inhabiting the freezing Chukchi Peninsula in East Russia. Indigenous people inhabiting arctic regions often have diets very high in meat due to the conditions they live in being poorly suited for agriculture. As mentioned, dingoes and grey wolves only have two copies of the amylase gene, and Huskies have a not too dissimilar three. Salukis, on the other hand, were originally bred in the Fertile Crescent in the Middle East and would have had the longest time to adapt to agriculture, having 29 copies of the gene, allowing them to digest starch much more easily.

Dogs did not just follow humans into different latitudes but also different altitudes, as there are several dog breeds known to have been bred in mountainous conditions. Tibetan Mastiffs, for example, are from the Himalayas and are sometimes permanent inhabitants of villages at heights of 4,000 meters. As their owners adapted to the lower oxygen levels present here, so did they.

Interestingly, this was probably from breeding with a Tibetan wolf. After the domestication of dogs, there have been many incidences of them breeding with wild populations, and this gene flow is one of the reasons why genetic studies between wolves and dogs can be difficult to conduct. This breeding with the local wolf populations allowed them to develop resistance to hypoxia in these harsh conditions, and they were able to adapt much faster than the other domesticated animals in the region, such as yaks.

Surprisingly, this is also the way that people living in the Himalayas acquired their genes that allow them to inhabit these regions, as well as species of archaic humans known as the Denisovans. They occupied large parts of Asia and coexisted with Homo sapiens and are known to have interbred. Denisovans were close relatives of Neanderthals and were adapted to high altitudes, being found in many different Asian mountain ranges.

There is some recent research that shows that Tibetans are inheritors of the ancient and evolved trait of being able to regulate blood oxygenation, just like the Tibetan Mastiff and wolves. It could be argued then that the early relationship with dogs was actually best described as a natural symbiosis, like how African oxpeckers feed on the back of large African mammals or cleaner fish clean large fishes. Dogs and humans benefited each other, and like many animals that have formed symbiotic relationships, they actively co and convergently evolved to maximize this beneficial relationship.