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How Humans Have Changed Dogs' Brains — and Their Behaviors

Analysis by Dr. Karen Shaw Becker

dog breeds

Story at-a-glance -

  • A recently published study proves that centuries of selective breeding have reshaped dogs’ brains and altered their behavior
  • Using MRI scans, researchers concluded that differences in behavior among dog breeds were directly related to differences in the structure of their brains
  • The lead study author observed that human brains “are changing other brains on the planet”
  • Thankfully, selective breeding for specific behaviors in dogs hasn’t so far resulted in some of the tragic outcomes seen in dogs selectively bred to “enhance” certain physical features

A fascinating new study suggests that centuries of selective breeding have reshaped dogs' brains and altered their behavior.1 Said another way, the differences in behavior we see from one dog breed to the next are related to variations in the brain network structures among the breeds.

Researchers Evaluated 62 Dogs, 33 Breeds, and 10 Behavior Specialties

A team of university scientists analyzed the MRI scans of 62 male and female purebred dogs (pets living with U.S. families) from the following 33 breeds:2

Basset Hound

English Pointer

Pit Bull

Beagle

German Shorthaired Pointer

Siberian Husky

Bichon Frise

Golden Retriever

Silky Terrier

Border Collie

Greyhound

Springer Spaniel

Boston Terrier

Jack Russell Terrier

Standard Poodle

Boxer

Keeshond

Weimaraner

Bulldog

Labrador Retriever

Welsh Corgi

Cavalier King Charles Spaniel

Lhasa Apso

West Highland White Terrier

Cocker Spaniel

Maltese

Wheaten Terrier

Dachshund

Miniature Schnauzer

Whippet

Doberman Pinscher

Old English Sheepdog

Yorkshire Terrier

The breeds were assigned to one or more of the following 10 groups according to their "behavioral specialization" per the American Kennel Club (AKC):

1. Scent hunting — Basset Hound, Beagle, Dachshund

2. Companionship — Bichon Frise, Boston Terrier, Bulldog, Cavalier King Charles Spaniel, Keeshond, Maltese, Yorkshire Terrier

3. Herding — Border Collie, Old English Sheepdog, Welsh Corgi, Wheaten Terrier

4. Vermin control — Boston Terrier, Dachshund, Jack Russell Terrier, Miniature Schnauzer, Silky Terrier, West Highland White Terrier, Wheaten Terrier, Yorkshire Terrier

5. Sport fighting — Boston Terrier, Boxer, Bulldog, Pit Bull

6. Sentinel work — Boxer, Doberman Pinscher, Keeshond, Lhasa Apso, Wheaten Terrier

7. Police work — Boxer, Doberman Pinscher

8. Bird retrieval — Cocker Spaniel, English Pointer, German Shorthaired Pointer, Golden Retriever, Labrador Retriever, Springer Spaniel, Standard Poodle

9. Sight hunting — Greyhound, Weimaraner, Whippet

10. War — Boxer, Doberman Pinscher

Study Results Show Dogs' Brain Anatomy Varies Significantly as a Result of Human-Selected Breeding for Specific Behaviors

The researchers observed that differences in behavior among breeds were directly related to differences in the structure of the dogs' brains. The MRI scans showed differences in the same, distinct brain networks among different breeds, which suggests those distinct networks correspond to differences in behavior.

Before they could draw their conclusions, however, the researchers had to identify distinct, primarily independent brain regions in order to see if they differed among breeds. They identified six brain regions:

One related to social bonding to humans

One related to conscious responses to tastes and smells

One related to moving through the environment

One related to action and interaction

One related to affected processes linked to fear, mating, and aggression

One related to processing smells and visual stimuli

The researchers concluded that:

"Neuroanatomical variation is plainly visible across breeds. This variation is distributed nonrandomly across the brain. A whole-brain, data-driven independent components analysis established that specific regional subnetworks covary significantly with each other. Variation in these networks is not simply the result of variation in total brain size, total body size, or skull shape.

Furthermore, the anatomy of these networks correlates significantly with different behavioral specialization(s) such as sight hunting, scent hunting, guarding, and companionship. Importantly, a phylogenetic analysis revealed that most change has occurred in the terminal branches of the dog phylogenetic tree, indicating strong, recent selection in individual breeds.

Together, these results establish that brain anatomy varies significantly in dogs, likely due to human-applied selection for behavior."3

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Human Brains Are 'Changing Other Brains on the Planet'

"The biggest wow moment for me was just looking at the scans," study leader Erin E. Hecht, an evolutionary neuroscientist at Harvard University, told National Geographic. "It's really cool in science where you have a result where you don't have to do any fancy statistics to be able to tell there's something going on."4

Hecht and her study co-authors also performed a statistic analysis that shows the brain variations occurred relatively recently, suggesting that the evolution of dogs' brains has happened quickly.

"It brings home how humans alter the world around them," said Hecht. "It's kind of profound that our brains are changing other brains on the planet."

Hecht makes an insightful observation here — one that should give us pause. The expression "With great power comes great responsibility" seems to apply. If we have the power to alter the brains of other species, we also have a solemn responsibility to wield that power for the benefit of those species and not for our own benefit. The same applies to our ability to alter the environment.

With one or two exceptions, I don't see any glaring problems at the moment with the ways in which dogs' brains, and therefore their behaviors, have been changed through selective breeding. Let's hope it stays that way.

Irresponsible Selective Breeding Can Have Tragic Consequences

When it comes to selective dog breeding practices to achieve certain physical characteristics, I'm not encouraged by the "improvements" that have taken place over the last 100 years or so. Breeding physically resilient, healthy dogs has been replaced with breeding for the sole purpose of attaining twisted beauty pageant awards, and breeding for esthetics has cost us the health of our most beloved breeds.

As a veterinarian, I've seen first-hand the problems created when dogs are bred exclusively to achieve specific features, without concern for their health, mobility, or quality of life. It is deeply disturbing to me, with all we know about the suffering these animals endure, that breeders persist in exaggerating their dogs' physical characteristics, even if it means sacrificing their health, and national kennel clubs condone it.

The following images on the left are from a 1915 book titled Dogs of All Nations. The pictures on the right are today's poorly bred version of the dog on the left.

Bull Terrier
By: Science and Dogs

On the left is a well-conditioned, athletic Bull Terrier. The dog on the right has an altered skull and thick abdomen. Today's Bull Terriers are prone to a long list of disorders, including extra teeth and compulsive tail-chasing.

Basset Hound
By: Science and Dogs

Look at how low to the ground today's Basset Hound is. His shorter stature is the result of changes to the rear leg structure. He also has surplus skin, and needlessly long ears. Today's Basset Hound's droopy eyes are prone to eyelid abnormalities, and he also often suffers from problems related to his vertebra.

Boxer Dog
By: Science and Dogs

See how much shorter the Boxer's face on the right is? Boxers are brachycephalic dogs, meaning they have pushed-in faces. Like many brachy breeds, the Boxer's already short muzzle has been bred even shorter over the years, and slightly upturned as well. Brachys have difficulty breathing and controlling their body temperature, which often places extreme limitations on their physical abilities.

English Bulldog
By: Science and Dogs

This unfortunate animal is the poster dog for all that is wrong with exaggerated breeding for looks. English Bulldogs suffer from an endless list of diseases, and according to one survey, their median age of death is 6.25 years. The massive size of today's English Bulldog makes normal mating and birthing out of the question. They can't reproduce without medical intervention.

Dachshund
By: Science and Dogs

Dachshunds a century ago had short but functional legs and necks in proportion to their overall size. Since then, they have been bred for longer backs and necks, jutting chests, and legs so short their bellies barely clear the floor. Doxies have the highest risk of any breed for intervertebral disc disease, which can cause paralysis. They are also prone to dwarfism-related disorders, progressive retinal atrophy (PRA), and leg problems.

German Shepherd
By: Science and Dogs

The German Shepherd Dog is another animal that has been ruined by unscrupulous breeding practices. In 1915, the GSD was a medium-sized dog averaging 55 pounds. Today's GSD is a complete distortion of the original. He's a good 30 pounds heavier, with a barrel chest, sloping back, and often a "drunken" gait. These dogs used to be magnificent athletic specimens, but no more.

Pug Dog
By: Science and Dogs

The Pug is another brachycephalic dog that has been bred to exaggerate the trait. The result? High blood pressure, heart problems, low blood oxygen levels, breathing problems, a tendency to overheat/develop heatstroke, dental issues, and skin fold dermatitis. At the other end of this poor dog is a "highly desirable" double-curl tail, which is actually a genetic defect that can result in paralysis.

Saint Bernard
By: Science and Dogs

Today's version of this once-highly skilled working dog is supersized, with a pushed-in face and excess skin. The Saint Bernard doesn't do much work these days, because he quickly overheats. Some of the diseases he's prone to include eye and eyelid abnormalities, Stockard's paralysis (a spinal cord disorder), and bleeding disorders. I agree with the Science and Dogs blogger who concludes:

"No dog breed has ever been improved by the capricious and arbitrary decision that a shorter or longer or flatter or bigger or smaller or curlier 'whatever' is better. Condemning a dog to a lifetime of suffering for the sake of looks is not an improvement; it is torture."5

We need to do better for our dogs.