Dog facts

• There are almost 400 breeds of domestic dog.¹
• Dog domestication may have begun as early as 35,000 years ago and was certainly underway by 14,000 BC. ²
• Dogs are the most widespread carnivores in the world. With an estimated population of one billion individualsthey are present in nearly all areas where humans live. ³
• It’s estimated that a dog’s sense of smell is 10,000 to 100,000 times more powerful than a human's.⁴ Dogs can detect scents at thresholds as low as one part per trillion (ppt). ⁵
• Dogs may be able to perceive ultraviolet lightor even sense the Earth’s magnetic field through their eyes.⁶
• Dogs are omnivores and can satisfy their nutritional needs with either meat or plant-based foods.
• Dogs wag their tails asymmetrically. They show a right-side wagging bias when happyand a left-biased wagging when stressed.⁷
• A dog’s lifespan is largely determined by its breed. In generalsmaller breeds tend to live longer.⁸ Giant breeds such as the great Dane live on average just 6.5 yearswhile lapdogs such as the toy poodle can expect to live 14.6 years.⁹
• When they want to playdogs often produce a sort of breathy snorting sound that resembles laughter.¹⁰

It's thought that the process of canine domestication may have begun as early as the Upper Palaeolithic periodapproximately 35,000 years agoand was certainly underway by 14,000 BC.¹¹ Through DNA analysiswe know that dogs separated from their wolf ancestors between 27,000 and 40,000 years ago.¹² There are even signs of dog burials 14,200 years agosuggesting dogs were considered part of the family by that point.¹³

Howeverit isn’t clear whether dog domestication first occurred in one placeor in multiple locations. We also don’t know why it happened. At this timehumans were still nomadic hunter-gatherers and had yet to settle down in farming communities. One theory is that people recruited dogs to help them hunt larger quarry. Another is that wolves could have fed on scraps of meat by the firesidewhere they slowly became more accustomed to people.

There are almost 400 breeds of modern domestic dogfrom the diminutive chihuahuato the labrador and Siberian husky.¹⁴ Each breed has unique traits that have been selected for by humans over hundredsif not thousandsof yearsalthough understanding the genetic basis of these traits has confounded scientists. Artificial selection has led to a huge diversity of breeds of all different shapes and sizes.

We tend to view different breeds as having specific personalities – labradorsfor exampleare seen as loyalwhile spaniels are viewed as high-spiritedirrepressibly energetic and hyperactive. Howeverstudies have shown that breed is not a good predictor of a dog's behaviour or temperament. Researchers surveyed the owners of more than 18,000 dogs to learn more about their pets’ personalitiesthen sequenced the DNA of 2,100 of these dogs.¹⁵ The scientists identified 11 genetic regions that were strongly associated with dog behaviourssuch as friendliness and howling frequencyyet none of the genes or behaviours were specific to any one breed. The study concluded that a dog’s breed could only explain around 9% of its behaviour.

A dog’s lifespan is largely determined by its breed andin generalsmaller breeds tend to live longer.¹⁶ Giant breeds such as the great Dane live on average just 6.5 yearswhile lapdogs such as the toy poodle can expect to live 14.6 years.¹⁷ While the average dog may live for 12 yearssome dogs have been known to live in excess of 27 years.¹⁸

One study found that the longest-lived pure breeds are the miniature poodlebearded collieborder collie and miniature dachshundwhile the shortest-lived are the Dogue de Bordeaux and great Dane.¹⁹ Crossbred or "mongrel" dogs live on average 1.2 years longer than purebred dogs. The reason for this is thought to be because the selective breeding of purebred dogs leads to a higher rate of inbreeding. This increases the risk that harmful genes will accumulate in the population. ²⁰ Selecting for certain traits for aesthetic reasons can also harm the health of purebred dogs. One 2024 study found that the shortest-lived dogs were medium-sized dogs with flat facessuch as English bulldogsFrench bulldogs and shih tzus.²¹ Flat-faced dogs are known to face health problems such as issues with breathing and digestionwhich may explain their shorter lives.

It's not known why larger breeds tend to live less longalthough one theory is that their rapid growth makes them more susceptible to cancer.  This was backed up by one study which found that the likelihood of dying from cancer steadily increases with a dog's weight.²²  According to the authorsa 30kg (65lb) dog is 50 percent more likely to die of cancer than a 3kg (7lb) dog.

The notion that dogs can only see in black and white is a mythalthough it is likely that dogs view the world in a very different way from humans. In mammalscolour perception begins at the back of the eye in the region known as the retina. Therespecial light-sensitive cells called cones detect photons of light. Humans have three types of cone receptorswhich respond to redblue and green light respectively. By combining signals from all three coneshumans can perceive thousands of different colours. Dogson the other handhave just two types of cone cells: blue and yellow.²³ This suggests that dogs may experience a kind of colour blindnesswhere they are unable to perceive differences between greenyellow and red cues. Howeverthe experimental evidence backing this up is mixedwith some studies finding that dogs struggle to discriminate certain colours. ²⁴ Other studies show they can pick out redblue and green objectsalbeit not as well as humans.²⁵

There is some evidence that dogs may be able to perceive ultraviolet light, or even sense the Earth’s magnetic field through their eyes.²⁶ A recent study observed the presence of cryptochrome 1a special protein located in the canine eye that is sensitive to blue light. Cruciallythe protein’s response to light is determined by the orientation of the Earth’s magnetic field.²⁷

Unlike humanswho see very poorly in low lightcanines have excellent night vision. This is partly because their retina is largely composed of rod photoreceptorsa special type of cell that is extremely sensitive to dim light.²⁸ In dogs97% of retinal cells are rodscompared with 95% in humans.²⁹

Dogs also have a special structure in their eye that helps them see in the darkcalled the tapetum lucidum. This mirror-like membranefound in most vertebrates - although not in humans - sits behind the retina and reflects light back on to itgiving receptors two chances to be activated by incoming photons of light.³⁰ The tapetum is the reason dogs’ eyes appear to glow in the dark when you shine a light on them.

Interestinglybreeds of dog appear to differ in the relative size of their tapetum lucidum. Generallysmaller sized breeds such as dachshundsminiature poodlesand cavalier King Charles spanielshave a smaller tapetal areawhile larger dogslike border colliesgolden retrievers and English springer spaniels typically have a full-sized tapetal area.³¹ A large proportion of labradors lack a tapetal area altogetheralthough there is no evidence showing that this affects their night vision. 

There’s nothing better than the rhythmical beating of your pooch’s tail as it greets you when you walk through the door. A wagging tail can signify that a dog is pleased or excited to see youbut studies have shown that this behaviour is more complicated than first appears.

While it’s true that dogs wag the most when their owners are presentstudies have shown they also wag their tails in response to food.³² Some dogs also wag their tails when they are stressedsuch as when they encounter an aggressive dog. In such casesthe height of the wagging tail can also convey important informationa low tail conveying appeasementsubmission or non-aggressive intent.³³

Dogs also don’t wag their tails symmetrically.³⁴ They exhibit a right-side wagging bias when presented with stimuli that has a positive emotional significance to themsuch as a photo of their owner or a familiar person. On the other handthey show left-biased wagging for stressful stimulisuch as when shown an unfamiliardominant dog or when in aggressive situations. One study that investigated how adult beagles interacted with humans showed that the dogs shifted their wagging from a left- to right-side bias as the dogs became more familiar with the person conducting the study.³⁵

Domestic dogs wag their tails much more frequently than wolves.³⁶ In factdifferences in dog and wolf tail-wagging behaviour appear as early as three weeks of ageeven when pups of both species have been raised in the same way.³⁷

So why is this? It’s possible thatover timehumans have consciously or unconsciously bred dogs that wag their tails more often and more rhythmicallyperhaps because they find the rhythmic motion endearing or appealing. This is called the ‘domesticated rhythmic wagging’ hypothesis.³⁸ 

Howeveranother theory that could explain why dogs wag their tails so much is known as the 'domestication syndrome' hypothesis. The idea holds that humans could inadvertently have caused tail wagging in dogs to become more exaggerated over time by selectively breeding for other traits such as tameness or friendliness towards humans. This could occur if the genes for tail wagging were located physically close to those that control fear or friendlinessfor example.

Support for the domestication syndrome hypothesis comes from a long-term experimentin which scientists bred silver foxes (Vulpes vulpes) for over 40 generationsselecting specifically for tameability and docility.³⁹ Even though tail wagging was not directly selected forthe tamed foxes exhibited dog-lke talil wagging behaviour and developed more curled tails. This suggests that the genes related to tail wagging could be located physically close to genes associated with docility and tameness.

The main difference between the domesticated rhythmic wagging and domestication syndrome hypotheses is that the first suggests humans consciously or unconsciously selected for dogs that wag their tailswhile the second suggests that tail wagging is linked to other desirable traits.

Unlike catswhich need to eat meat to survivedogs are omnivores and can therefore satisfy their nutritional needs with either meat or plant-based foods.

Anyone who owns a pet pooch will know that they go wild for cooked chickenbeefduckand turkey. Howeverless well known is that dogs also love to snack on tasty vegetable treats such as carrotscucumbers and peas. Fruits such as apples and blueberries will also go down well.⁴⁰

Some foods that are considered healthy for humans are harmful to dogs. Raisinssultanas and grapes are potentially lethal and can cause kidney failureseizures and death. Chocolate and coffee can also be deadly.

Other foods that are harmful include avocadocherriesmacadamia nuts and cinnamon. Onionsgarlics and chives contain substances called organosulphoxideswhich are also toxic to dogs.

It’s estimated that a dog’s sense of smell is 10,000 to 100,000 times more powerful than that of a human's.⁴¹ Dogs can detect scents at thresholds as low as one part per trillion (ppt). ⁴² It’s not just bloodhounds – even chihuahuas and yorkies have an extraordinary ability to sniff and track scents. The reason for this is down to the number of smell receptors in the nose: humans have around five millionwhile dogs have around 220 million.⁴³ Dogs have been known to scent odours from 12 miles (20km)  away.⁴⁴

Intriguinglya 2022 study found that there is a direct connection between a dog’s olfactory bulbwhich is responsible for smelland their occipital lobewhich processes vision. This suggests dogs’ brains are capable of integrating information on sight and smell to help them perceive the world.⁴⁵

Dogs can even smell human emotions such as fear. In one studyhuman participants viewed videos designed to elicit feelings of fearhappinessor a neutral response. Samples of sweat were then taken from the volunteers and presented to dogs.⁴⁶ The study showed that dogs that sniffed sweat from a fearful human showed more signs of stress than those exposed to happy or neutral smells. They also had higher heart rates.

Dogs are also able to sniff out signs of illness in humans. Some are even being trained to detect scents that serve as early warning signs for cancersevere allergic reactionsepileptic fits and narcolepsy.

In his book The Descent of Manbiologist Charles Darwin suggested that dogs may have a sense of humourwriting:⁴⁷

"If a bit of stick or other such object be thrown to onehe will often carry it away for a short distance; and then squatting down with it on the ground close before himwill wait until his master comes quite close to take it away. The dog will then seize it and rush away in triumphrepeating the same manoeuvreand evidently enjoying the practical joke."

Darwin isn’t the only person to notice this propensity of pooches to play tricks on their owners. When they want to playdogs often produce a sort of breathy snorting sound that sounds a little like laughter.⁴⁸ In one studyresearchers played this sound to dogs at a rescue shelter. The results showed that listening to dog "laughter" made the shelter dogs calmer and less stressed.⁴⁹

Of all the adorable dog quirksthe head tilt may be the most endearing. Yet the reasons behind this behaviour – when a dog cocks its head to one side to look quizzically at you – aren’t fully understood.  Possible explanations include to hear betterto listen for specific sounds or to see past their muzzlesbut there is little evidence to support either. However a 2021 study may shine a light on the phenomenon.⁵⁰

Researchers were investigating “gifted” canines – dogs who can quickly memorise and recall the names of many different toys. In a series of experimentsthey asked the dogs (who were all border collies) to find and locate a specific toyand compared their success with that of normal dogs. Interestinglythe study showed that not only were the gifted dogs much better at recalling the names of different toysbut they also tilted their heads much more frequently. In factthe scientists found that when asked to retrieve a toythe "gifted" dogs cocked their heads 43% of the time, while the "normal" dogs did so just 2% of the timeleading the researchers to believe the behaviour could signify high attentiveness or concentration.

Feature image © Gregg Lippert | Unsplash

Fun fact image © Gursimrat Ganda | Unsplash

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