Why Most Dogs Are Actually the Same: Study Reveals Surprising Biological Truth

For centuries, humans have carefully bred dogs to create distinct breeds tailored for specific roles—hunting, herding, guarding, retrieving, or simply being adorable companions.

These efforts have given us a wide range of breeds, each with its own look and personality. But what if all that visual variety didn’t actually reflect meaningful biological differences?

A new study led by Dr. Nicholas Hebdon at Chapman University has revealed a surprising truth: almost all dogs are biologically the same beneath the surface.

Despite the dizzying array of breeds, from the towering Irish Wolfhound to the compact poodle, data now shows that the physical differences between them are far more superficial than we thought.

Skulls May Vary in Size, But Not in Shape

Dr. Hebdon and his team analyzed 117 skulls from 40 different dog breeds and compared them to those of 18 wild animals, including wolves and red foxes.

Using 3D scanning and more than 40 anatomical reference points on each skull, they searched for meaningful structural differences that might explain why some dogs are better at certain jobs than others.

To their astonishment, they found virtually no variation in skull shape across the breeds studied. Aside from size differences, a Labrador, a Border Collie, a Borzoi, and a Dachshund all shared the same basic cranial structure.

That’s right—the scent-driven bloodhound and the speed-loving greyhound are, structurally speaking, working with the same skeletal design.

The only real exceptions were the brachycephalic, or flat-faced, breeds like pugs, French bulldogs, and English bulldogs.

These dogs have undergone such extreme breeding for a “squashed” facial appearance that their skulls are measurably different—and often not in a good way.

These differences are less about function and more about form, leading to respiratory issues and other health problems.

Breed Differences Aren’t Biological—They’re Emotional

This study turns long-held assumptions upside down. If dogs don’t have physical adaptations that make them better at specific tasks, how do we explain the Border Collie’s herding prowess or the spaniel’s sniffing talent?

According to Dr. Hebdon, the answer lies not in biology but in psychology. “Breeds have a specific personality that makes them really want to do those jobs,” he explains.

“It’s that increased motivation that makes them good at the job, rather than some physical or biological change that humans have encoded.”

In essence, breeders have selected for temperament and enthusiasm over anatomical differences.

A Belgian Malinois doesn’t guard because it has a special bite or brain—it guards because it wants to. A Labrador doesn’t guide because it’s shaped a certain way—it does so because it has a calm, trainable disposition.

This subtle but profound insight changes how we think about the very nature of a “working dog.”

Pitbull Myths and the Power of Perception

The study also takes aim at one of the most persistent dog myths: the idea that pit bulls have a unique skull shape or a so-called “locking jaw” that makes them inherently dangerous.

Dr. Hebdon’s team found no such structural difference. In terms of bone, a pit bull’s skull is no more specialized than that of a spaniel or setter.

This finding reinforces the idea that dog behavior is more influenced by environment and training than by innate physical traits.

It’s a powerful rebuttal to breed-based prejudice and underscores the importance of judging dogs by their actions—not their appearances.

Rethinking the Role of Breeding

For generations, we’ve assumed that selective breeding has created functional machines: sniffer dogs, herders, guards, and companions, each honed to perfection.

But this research suggests something more nuanced. In pursuing certain traits, humans have changed the outer appearance of dogs far more than their inner workings.

“Underneath those various aesthetic qualities,” Dr. Hebdon explains, “most dogs are working with the exact same biological toolkit.”

In other words, breeders didn’t necessarily design dogs for tasks—they simply reinforced behaviors that were already present, leading to emotional predispositions rather than anatomical specializations.

The Takeaway: Dogs Are More Alike Than Different

This groundbreaking study challenges the very foundation of what we think we know about dog breeds.

While it’s still true that certain breeds are more suited to specific roles, it’s not because they’re biologically engineered for them. It’s because they’re emotionally inclined, eager, and excited to do what they love.

So, the next time you see a dog excelling at a task—be it sniffing out truffles, rounding up sheep, or comforting a human—you’re not witnessing the result of some complex anatomical advantage.

You’re seeing motivation, personality, and years of human partnership at work.

And perhaps, in realizing that dogs are more similar than different, we’ll learn to appreciate them not just for what they look like, but for the hearts and minds behind those wagging tails.