If you’re a dog lover, you’ve probably favourited the top viral video of 2009: “Bizkit the sleeping dog.” In the video, a sleepwalking dog named Bizkit, most likely dreaming about an intense squirrel chase, runs into a wall, hard! No other video in 2009 has garnered so many “awww” and “go get ’em, boy” comments.
Having a pet dog seems to connote a certain personality type. My older brother tells me how his Yorkshire Terrier is to girls as honey is to bees (while my aggressive Cocker Spaniel leads to more lawsuit threats than phone numbers). Dog owners are seen as warm and responsible individuals. Those who jog with their dog are further characterized as assertive, and people who enjoy slobbery kisses from their dogs are affectionate (albeit a bit weird).
Indeed, dog domestication is a peculiar thing. Why have humans chosen to align themselves so closely with this animal? And why have dogs chosen to participate in this relationship?
Dogs and humans have become each other’s best friends for four purposes: herding and hunting, an early alarm system, a food source for dogs, and companionship for humans.
Based on the analysis of mitochondrial DNA, genetic evidence suggests that dogs split from wolves around 100,000 years ago. A skull discovered from the Goyet Cave in Belgium, dated 31,700 BP, is believed to be a wolf in transition to a dog, as indicated by the shortened snout. The earliest domesticated dog found in China is from the early Neolithic (9,000-7,800 BP) Jiahu site in Henan Province. European Mesolithic sites like Skateholm (7,250-5,700 BP) in Sweden contain dog burials, proving the value of dogs to hunter-gatherer settlements. Danger Cave in Utah has the earliest evidence of dog burial in the Americas, from around 11,000 years ago. It’s clear that dog domestication started long ago, even further back than scientists believed as recently as 2008.
A study published in Proceedings in the National Academy of Sciences says that dog domestication may have originated in North Africa, as opposed to East Asia as previously thought. Adam Boyko, research associate in the Department of Biological Statistics and Computational Biology at Cornell University, and his colleagues looked at three genetic markers for 318 village dogs from seven regions in Egypt, Uganda, and Namibia. The scientists performed a DNA analysis on a number of putatively African dog breeds, Puerto Rican street dogs, and mixed breed dogs from the United States.
The scientists determined genetic diversity was just as high for the African dogs as it was for the East Asian village dogs that were the focus of the earlier research.
What is most interesting, however, is where domestication is taking the dog species. More specifically, the breeding practices have some serious implications on trait diversity.
Dog breeding is defined as intentional mating to produce certain qualities in offspring. These qualities typically involve size, colour, and fur, and have resulted in greater genetic and phenotypic diversity.
A study published in The American Naturalist compared the skull shapes of domestic dogs with those of different species across the order Carnivora, the wider lineage that includes dogs, cats, bears, weasels, and even seals and walruses. The analysis found that in domestic dogs, skull shapes varied as much as those of this whole group, and that the extremes in diversity were farther apart in domestic dogs than in the rest of the order. For instance, the difference in skull shape between a Collie and a Pekingese is greater than between a cat and a walrus.
“We usually think of evolution as a slow and gradual process,” co-author Abby Drake of the College of the Holy Cross in Worcester, Massachusetts told World Science. “But the incredible amount of diversity in domestic dogs has originated through selective breeding in just the last few hundred years, and particularly after the modern purebred dog breeds were established in the last 150 years.” By contrast, the Carnivora as a whole date back at least 60 million years.
“Domestic dogs don’t live in the wild, so they don’t have to run after things and kill them—their food comes out of a tin and the toughest thing they’ll ever have to chew is their owner’s slippers,” Klingenberg said. “So they can get away with a lot of variation that would affect functions such as breathing and chewing and would therefore lead to their extinction.”
Natural selection—the set of environmental pressures that drives species to evolve as they adapt to changing environments—has been relaxed for pet dogs. In its place humans employ artificial selection, manipulating evolution to obtain favourable features such as a “cute” appearance. “Dogs are bred for their looks, not for doing a job, so there is more scope for outlandish variations,” said Drake.
Dog domestication also has strong implications for understanding human social behaviour. Cooperation, attachment to people, the ability to imitate, and understanding human verbal and non-verbal commands are just a handful of the social behaviours we share with dogs. A publication in the journal Advances in the Study of Behaviour suggests that shared environment has led to the emergence of functionally shared behavioural features in dogs and humans and, in some cases, functionally analogous underlying cognitive skills.
“In my view, pet dogs can be regarded in many respects as ‘preverbal infants in canine’s clothing,’” lead author Jozsef Topal told Discovery News, adding that many dog-owner relationships mirror human parental bonds with children.
In one of many recent studies conducted by the team, Topal and his colleagues taught both a 16-month-old human child and mature dogs to repeat multiple demonstrated actions on verbal command—“Do it!” shouted in Hungarian.
The actions included turning around in circles, vocalizing, jumping up, jumping over a horizontal rod, putting an object into a container, carrying an object to the owner or parent, and pushing a rod to the floor.
The dogs “performed surprisingly well and at a comparable level to the 16-month-old child,” Topal added.
The study supports the notion that dogs exhibit all three types of social behaviour that humans developed when they split from chimpanzees six million years ago. These include sociality, loyalty, and reduced aggression. The second is synchronization, where following social rules strengthens group unity. And the third is constructive reality, whereby dogs cooperate and communicate to achieve shared goals.
Human social behaviour is also very fluid and dependent on environment. How it changes dog domestication and interspecies relations is still unknown.
The human-dog relationship is unique to evolutionary history. After all, what wouldn’t we do for man’s best friend?
