Dog

• 1. Introduction

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  The dog buried at Bonn-Oberkassel, Germany, lay beneath thick basalt blocks alongside a man and a woman, all three dusted with red hematite powder. Dated to 14,223 years ago, this animal had survived canine distemper as a puppy. Survival from that illness without intensive human care is unlikely, and it happened at an age before the dog could serve any practical purpose. Someone fed it, nursed it, and kept it alive for no reason but attachment. That grave holds a question. Why did a hunter-gatherer choose to care for a sick animal, long before farming, long before anyone needed a worker? The answer reaches back further than agriculture itself. Dogs were the first species humans ever domesticated. Carl Linnaeus gave them a Latin name, Cerberus guarded the gates of Hades, and somewhere along the way they earned the title of man's best friend. This is the story of how a wolf became a companion, and what that bond cost and gave on both sides.

• 2. From Wolf To Companion

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  Genetic studies place the split between dogs and wolves somewhere between 27,000 and 40,000 years ago. A 2021 literature review infers that domestication happened in Siberia around 23,000 years ago, carried out by ancient North Siberians. From there, dogs dispersed eastward into the Americas and westward across Eurasia. They likely traveled with the first humans to reach the Americas. The path into domestication was probably commensal. Wild dogs ate refuse from human camps, and at first the humans neither benefited nor were harmed. All ancient and modern dogs descend from an extinct wolf population distinct from any living wolf lineage. The questions of exactly when and where remain uncertain, with proposed origins in Europe, the high Arctic, or eastern Asia. A 2018 study found 429 genes that differ between modern dogs and wolves. Because those same differences appear in ancient dog fossils, researchers tied them to the initial domestication rather than to recent breeding. The genes are linked to neural crest and central nervous system development. They affect embryogenesis and can produce tameness, smaller jaws, floppy ears, and reduced craniofacial development, the cluster known as domestication syndrome. The study concluded that the earliest selection was for behavior, not appearance. A 2016 study sharpened this further, finding only 11 fixed genes that varied between wolves and dogs, many affecting the fight-or-flight response. The traits that make a dog approachable may share genetic ground with Williams-Beuren syndrome in humans, which produces hypersociability at the expense of problem-solving ability.

• 3. The Shape Of A Breed

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  Around 450 official dog breeds exist, the most of any mammal, and most descend from small numbers of founders within the last 200 years. Dogs began diversifying in the Victorian era, when humans took control of their natural selection. The skull, body, and limb proportions between breeds show more variation than exists across the entire order of carnivores. Consider the extremes. The Great Dane reaches 50 to 79 kilograms and 71 to 81 centimeters, while the Chihuahua sits at 0.5 to 3 kilograms and 13 to 20 centimeters. All healthy dogs share the same number of bones, with the exception of the tail. Selective breeding has stretched the skeleton larger for mastiffs and shrunk it for terriers. Dwarfism was bred deliberately into dachshunds and corgis, where short legs are prized. Three basic skull shapes emerged. The elongated dolichocephalic head appears in sighthounds, the intermediate mesocephalic falls in the middle, and the short broad brachycephalic shape defines mastiff types. This rapid reshaping carried a hidden cost in the breeding room. Mating close relatives, half-siblings or full siblings, is common practice for pet dogs. An analysis of 42,855 Dachshund litters found that as the inbreeding coefficient rose, litter size fell and the share of stillborn puppies climbed. In a study of Boxer litters, 22 percent of puppies died before reaching seven weeks of age, with stillbirth the most frequent cause.

• 4. A World Built On Smell

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  The dog brain is dominated by a large olfactory cortex, where the human brain is dominated by a large visual cortex. That single fact reorders how a dog experiences the world. Dogs carry roughly forty times more smell-sensitive receptors than humans, from about 125 million to nearly 300 million in breeds such as bloodhounds. Smell is the most prominent sense of the species. It lets a dog locate mating partners, sense stressors, and find resources by reading chemical changes in the air. Hearing runs nearly as sharp. Dogs can detect sound up to four times better than humans and pick up the faintest noises from about 400 meters, against 90 meters for a person. Vision is where dogs fall behind. Their sight is dichromatic, a world of yellows, blues, and grays, and they struggle to tell red from green. The dog's eye holds two types of cone cells against the human's three. One study found canine visual acuity up to eight times less effective than a human's. Beyond the familiar senses lies something stranger. One study suggests dogs can feel small variations in Earth's magnetic field. In calm magnetic conditions, they prefer to defecate with their spines aligned north to south. Stiff embedded whiskers fill in what the eyes miss, sensing vibrations and objects in low light, and likely guiding food toward the mouth.

• 5. The Talking Tail

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  A dog's tail is the terminal appendage of the vertebral column, a string of 5 to 23 vertebrae wrapped in muscle and skin. Most dogs naturally carry 26 vertebrae in their tails, though some with short tails have as few as three. One primary function is to broadcast emotional state. A study found that dogs wag asymmetrically depending on what they feel. Stimuli that invite approach produced higher-amplitude wags to the right side. The tail does mechanical work too. It helps the dog balance by shifting weight opposite the body's tilt, and it can spread scent from the anal gland through its position and movement. Some breeds carry a violet gland on the upper surface of the tail, marked by sebaceous glands, which may be vestigial or absent. When that gland enlarges it can leave a bald spot, sometimes caused by Cushing's disease. Tails can also be injured by forceful wagging, a condition called kennel tail, happy tail, bleeding tail, or splitting tail. In some hunting dogs the tail is traditionally docked to avoid injury, a practice opposed by the American Veterinary Medical Association and the British Veterinary Association. The evidence against it is stark. Around 500 dogs would need their tails docked to prevent a single injury.

• 6. Minds That Read Us

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  Rico, a Border Collie, knew the labels of over 200 different items. He worked out the names of unfamiliar objects by exclusion learning, and four weeks after first hearing a new word he still retrieved the right item. Another Border Collie, Chaser, learned the names of over 1,000 words and could pair them to verbal commands. Behavioral scientists suggest dogs possess social-cognitive abilities their canine relatives lack, abilities that run parallel to the skills of human children. Dogs carry about twice the neurons in their cerebral cortexes that cats do, which hints at roughly twice the intelligence. The skills are uneven, though, and revealing in their gaps. One study of 18 household dogs found they could not distinguish food bowls by location without other cues, suggesting a lack of spatial memory. Australian dingoes outperformed domestic dogs at non-social problem-solving, hinting that domestic dogs may have traded away problem-solving ability when they joined humans. The clearest sign of that trade comes from a single behavior. When given an impossible version of a task they had been trained to solve, dogs stared at the humans nearby. Wolves in the same situation avoided staring at humans altogether. The dog had learned to ask for help.

• 7. Living In Our World

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  The estimated global dog population in 2020 ran between 700 million and 1 billion, making the dog the most widely abundant large carnivoran in the human environment. Only about 20 percent live in developed countries. World Animal Protection estimated in 2011 that three-quarters of the world's dogs live as feral, village, or community dogs. Most survive as scavengers and have never been owned. When a stranger approaches a village dog, the most common response is to run away, at 52 percent, or to react aggressively, at 11 percent. Where dogs run loose, they reshape ecosystems. Dogs have made 11 vertebrate species extinct and have been linked to the extinction of 156 animal species. They are flagged as a potential threat to at least 188 threatened species worldwide. In New Zealand, a land with no indigenous land mammals before human settlement, that impact landed hard. Dogs also live alongside larger predators that hunt them. Leopards show a preference for dogs and will kill and eat them regardless of size. Siberian tigers in the Amur river region have taken dogs from the middle of villages, and striped hyenas kill dogs within their range. Losses of dogs to wolves have driven demands for more liberal wolf hunting regulations. The relationship with people remains the most lethal force of all, running in both directions, which the next chapter traces.

• 8. Best Friend And Casualty

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  An estimated 30 million dogs are killed and consumed across Asia every year, with China the largest consumer at 10 to 20 million annually and Vietnam at about 5 million. Humans have eaten dog meat for at least 14,000 years. The practice was once widespread in Southeast Asia, East Asia, Africa, and Oceania before religious change made it taboo. In South Korea, where the Nureongi has been the primary meat dog, attitudes shifted fast. A 2017 survey found under 40 percent backed a ban, but by 2020 the figure passed 50 percent. On the 9th of January 2024, the South Korean parliament passed a law banning the distribution and sale of dog meat, set to take effect in 2027. The danger runs the other way too. In 2018 the World Health Organization reported 59,000 people died globally from rabies, with 59.6 percent of deaths in Asia and 36.4 percent in Africa. Dogs are responsible for 99 percent of rabies cases worldwide. Children are the primary victims of dog bites and more likely to suffer serious injury. Yet the same animal offers comfort. When in a pet dog's presence, people show reduced cardiovascular and psychological signs of anxiety. Animal-assisted therapy has increased smiling and laughing among people with Alzheimer's disease. One role stands apart from all the rest. In 1957, the dog Laika became one of the first animals launched into Earth orbit aboard Sputnik 2, and died during the flight from overheating, a companion sent where no human had yet gone.