The science behind man’s best friend: the domestic dog

Name another species more universally beloved than the domestic dog. I’ll wait… Didn’t think so.

Across the globe, where you find us – Homo sapiens – you won’t have to look far before finding the domestic dog – Canis lupus familiaris.

From Chihuahuas to Great Danes, these paw-some pups come in a dizzying range of shapes, colours, sizes, and temperaments, but where did they come from?

Domestic dogs evolved from an ancient, and now extinct, wolf. Researchers have estimated, using genetic analysis, that dogs and wolves diverged around 27,000 to 40,000 years ago.

But exactly when, where, and how many times, dogs were domesticated by humans has been puzzling scientists for decades.

Doggy domestication

Scientists know that domestication happened in Eurasia and that that dogs are humanity’s earliest domesticated animal – predating agricultural animals like the goat and sheep, around 10,500 years ago.

The earliest undisputed fossil from a domesticated dog dates back to about 15 thousand years ago, from a site at Bonn-Oberkassel in Germany where archaeologists found a 28 week old puppy buried alongside grave goods and two humans. And while dog-like remains have been dated to more than 30,000 years ago, their status as dogs or wolves remains highly controversial.

Part of the right half of the lower jaw, fragment of the upper jaw, and teeth
Part of the right half of the lower jaw, fragment of the upper jaw, and teeth from the dog in the Bonn-Oberkassel grave. Credit: Thilo Parg/Wikimedia Commons. License: CC BY-SA 4.0

There isn’t consensus as to exactly why and how our pooches were domesticated, but there are a few hypotheses.

Some scientists suggest that cooperative hunting between wolves and humans led to domestication, with humans using wolves as tools for hunting megafauna. Another hypothesis suggests that humans may have captured and tamed wolf pups, raising them to adulthood and breeding them to eventually domesticate them.

Read more: Two ancient wolf populations which evolved into man’s best friend

But the dominant hypothesis is that wolves essentially domesticated themselves, invading human settlements to scavenge on animal remains and other edible waste. Over multiple generations they would have become gradually bolder and less fearful of humans, benefiting humans as either guards or hunting partners by living alongside them.

How did we arrive at the dog breeds of today?

Since domestication, humans have been selectively breeding dogs for desirable traits. Choosing dogs and their mates to reproduce useful traits, like decreased aggression and increased social capability, or aesthetic traits like coat colour or floppy ears, means that over time these characteristics become more prevalent in certain populations.

This year, researchers found that humans may have also been unconsciously selectively breeding dogs to have more expressive faces.

Drawings and sculptures have depicted different kinds of dogs for millennia, but it wasn’t until the Victorian era in England that dog breeds were first registered and codified. It was through the advent of competitive dog shows that new rules for controlled breeding were introduced, to produce a more uniform look for each breed, with dogs that perfectly represented the physical characteristics of their breed, rewarded in show.

Over time, that’s how we ended up with the 356 different dog breeds recognised by the International Canine Federation today.

Read more: Origin of dog breeds revealed

Dogs have a remarkable sense of smell

It’s due to several physiological factors. Some breeds such as bloodhounds, have up to 300 million scent receptors, while us humans only have around 6 million.

Their anatomy has also evolved to separate the functions of breathing and smelling when they inhale, thanks to a fold of tissue just inside their nostril. When dogs inhale, the airflow splits into two different paths: one continues down into the lungs for respiration, while the other is reserved for olfaction.

Dogs – but not humans – have an olfactory recess to house their scent receptors. When canines inhale, about 12 percent of the air travels into this special region at the back of the nasal cavity.

When they exhale, the air leaving the lungs bypasses this area entirely, leaving the scent-filled air undisturbed to allow for more time for odours to be absorbed. The exhaled air exits through the slits in the sides of their nostrils and the way the air swirls out actually help to bring in new odours to the dog’s nose, allowing them to sniff almost continuously.

They even have mobile nostrils, which allows them to determine the direction of the scent.

And incredibly, they can detect changes in human physiology, which is possible because illness and disease cause changes un the profile of gases – known as volatile organic compounds – emitted from our blood, urine, faeces, skin, and breath.

Medical-alert assistance dogs can identify changes in blood glucose levels for diabetics, and a 2021 study found that dogs can detect oncoming epileptic seizures from sweat samples.

Recent studies have even shown that dogs can accurately sniff out certain cancers, and infections like malaria and COVID-19.

This year, a small study even found that dogs could distinguish when people were stressed, accurately detect the breath and sweat samples from stressed participants 93.75% of the time.

Read more: New study suggests that dogs might be able to smell when we’re stressed

Did you know that dogs are colourblind?

When light hits a retina in the eye, it sets off chemical changes in cone cells, which respond differently to different wavelengths of light.

Humans have three types of cones, which means we have trichromatic vision and can see all wavelengths of light in the visible spectrum as distinct colours.

But a 1989 study found that dogs only have two types of cones in their eyes. Then, a 1995 analysis of canine vision determined that these two types of cones are sensitive to wavelengths that, in the visible spectrum, equate to two different hues: one in the violet and blue-violet range of light (430 to 475 nanometres wavelength), and the other in the greenish-yellow, yellow, and red wavelength range of light (500 to 620 nm).

So, from a dogs’-eye point of view the world is a mix of yellow and blue. For wavelengths between those two extremes, colours would appear less saturated, like blends of white or grey.

Read more: Dogs are colourblind

Regardless of where they came from and how long they’ve been with us, we can all agree that dogs make our lives better for being in them.

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