Dog science: Why do dogs have such a good sense of smell? And other canine questions answered

Dogs evolved around 15,000 years ago in China and are descended from the Asian wolf. DNA studies have shown that 95 per cent of the dogs in the world are descended from the same three females. This is probably because those ancestral dogs showed a special trait that made them much more useful to humans. Dogs are better than any other animal at correctly recognising and interpreting human social cues; better even than our closest relative the chimpanzee, and far better than a wolf. This is true even with puppies as young as nine weeks, which shows this is an innate ability, rather than something they learn from close association with us.

Originally dogs were kept exclusively for their hunting and defensive value but about 12,000 years ago, a mutation emerged that resulted in miniature dog breeds. Later, breeders began selecting for ‘cute’ features to create dogs that keep puppy characteristics into adulthood, such as floppy ears and rounder faces. At the same time, much of the pack instinct of many dog breeds was lost. Dogs became pets, rather than just weapons.

Dogs show more physical variation between breeds than any other domesticated animal. Genetically, the Tibetan Lhasa Apso and the Chinese Shih Tzu are closest to the ancestral dog but the earliest dogs would have been sight hounds, like the wolf. These are dogs that track their prey visually and rely on short bursts of speed to bring them down. They have long thin heads and long legs. Later, scent hounds emerged with shorter faces and short legs to keep their nose close to the ground. These dogs hunt game over much larger distances by following a scent trail and they use their superior endurance to exhaust an animal.


The anatomy of a dog
The anatomy of a dog

How intelligent are dogs?

The average domestic dog can exhibit social intelligence that’s seldom found in the animal world, even in our closest relative the chimp. Dogs can learn, and therefore be trained, in a number of ways by reinforcement (punishment and reward) and by observation. For instance, puppies will learn behaviour more quickly if they follow the examples set by older dogs and will even learn from watching humans perform tasks.

Dogs can demonstrate a sophisticated social cognition by associating behavioural cues with an abstract meaning, in tests dogs have successfully located a treat hidden under one of two buckets from a wide range of signals including taps, nods and even looks. In fact they out-performed chimpanzees, wolves and human infants at the task.

Why can dogs hear better than humans?

The biology of a dog’s ear compared to a human’s ear is quite different. Dogs also have a far wider hearing range than humans, allowing them to detect sounds far above a human’s auditory limit.

One of the major differences in biology is the size and shape of the outer ear. This is the part of the sensory organ responsible for catching sound. Dogs have far bigger outer ears, which are also mobile, and dogs use 18 muscles located in and around the outer ear to rotate, raise or lower the ear to aid hearing. They can identify a sound and its location much quicker than humans, and can hear sounds four times as far away as humans.

A dog's ear compared to a human's ear
A dog’s ear compared to a human’s ear

Facts about the dog hearing

Dogs hear at high frequencies

The average human hearing range is between 20Hz and 20,000Hz whereas a dog’s range is much higher from 40Hz to 60,000H.

Erect ears hear better

Dogs who have erect, pointy ears are noted to be able to hear slightly better than dogs with large, hairy ‘floppy’ ears.

Hearing is a dog’s secondary sense

Smell is thought to be the most important sense to a dog, but hearing comes in second over sight, taste and touch.

Dogs have impressive selective hearing 

Dogs can hear far more than a human, but have an ability to separate out sounds and focus on ones they want while ignoring others.

Dolphins have better hearing than dogs

Dolphins are actually thought to have the best hearing in the animal kingdom, with sound reception likely to take place in the lower jaw.

Why do dogs have such a good sense of smell?

A human nose might be able to detect more than one trillion smells, but it’s no match for a dog’s. Canines can sniff out explosives, drugs and even follow trails that are more than a week old.

They are able to do this due to the unique way their noses are set up. Humans have a single hole that takes in both air and smells, dogs have a flap of tissue that sends smells one way and air the other, allowing them to process the smells much more efficiently. They even have a system for the other direction, so while humans breathe out through their single nose hole and blow out any smells, dogs can exhale through a couple of small slits in their noses, meaning that any smell stays in their noses for a long time, allowing them to track scents for up to 210 kilometres (130 miles).

Canines’ advantage over humans extends right down to cellular level as well. They have about 230 million olfactory cells, the ones used for smelling, in their nose. By way of comparison, humans have to make do with anything between five and 40 million. No wonder they are always around as soon as you’re opening the dog-food tin!

However, dogs don’t just have this sense in order to sniff out their next meal. Their noses are pretty much equivalent to our eyes in terms of reading the world around them. When dogs inhale, they aren’t just picking up on scents. Their vomeronasal organ is at the bottom of their nasal passage and enables them to detect pheromones – chemicals that can reveal stacks of information about the other animals that have been in that area before them.

Dog science: Why do dogs have such a good sense of smell? And other canine questions answered
Their excellent noses make dogs some of nature’s best trackers

Can dogs smell cancer?

Dogs’ keen sense of smell has been put to work in the military, law enforcement and medical fields, but the latter has seen exciting new developments. Researchers at Pine Street Foundation in California trained five pooches to smell breast and lung cancer on a patient’s breath, and the results were 88 to 99 per cent accurate.

Other tests have shown that dogs can detect prostate and bladder cancer in urine. It’s thought that, after being trained to recognise the smell of hormones and pheromones in the urine of cancer patients, they are then able to sniff it out with great accuracy. They won’t replace medical tests any time soon, but can certainly play a part.

What causes that wet dog smell?

The smell of wet dog is pretty unpleasant. This distinct aroma actually comes from the excrement of small microorganisms, such as yeast and bacteria, which live within the animal’s fur. When these organisms come into direct contact with water, it breaks their chemical bonds, which in turn releases musky molecules into the air.

Leaving a wet dog to air dry can make the odour considerably more pungent. This is because when water evaporates off a surface it creates a relative humidity around it. As humid air can hold more molecules, this means you will get a much stronger whiff of wet dog.

Wet dog
Microorganisms that live in a dog’s fur are responsible for the wet dog stench

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