XL Bullies, Pitbulls, and German Shepherds are all infamous for their formidable bites, but new research has poured cold water on the idea that these fierce breeds actually bite any harder than other dogs.
Despite these breeds’ ferocious reputations, a new study shows that there is no functional difference in their skulls.
Likewise, the researchers found that the XL Bully’s ability to ‘lock’ its jaw is nothing more than a myth.
Researchers from Chapman University analysed 117 skulls from 40 domestic dog breeds and 18 wild relatives like wolves and foxes.
The researchers expected to find some differences in their skull shape.
However, their analysis revealed that there was ‘near full overlap’ between the skulls of Kennel Club-recognised breeds.
Co-author Dr Lindsay Waldrop says: ‘Dogs bred to bite things aren’t structurally different than dogs that have been bred to do other things.’
However, just because XL Bullies don’t have physiologically enhanced bite strength does not mean they aren’t more dangerous than other dog breeds.
Despite their fierce reputation, scientists say there is no evidence that dogs specifically bred for biting like XL Bullies (pictured) actually bite any harder than other dogs their size (file photo)
Dogs like German Shepherds have been selectively bred to have traits that make them good guard dogs. Scientists would expect these specifications to be reflected in their structural characteristics, known as their morphology (file photo)
From the time that dogs were first domesticated some 30,000 years ago, humans have selectively bred man’s best friend for a wide range of roles.
Since the creation of institutes like the Kennel Club, those roles have been formalised into the breed categories most of us would be familiar with.
Dr Waldrop says: ‘In the past 200 years, humans have created hundreds of dog breeds that look really different and are pretty specialized at some tasks like herding, protecting, and detecting odors.’
In nature, when an animal specialises for a task like sniffing out food or hunting at night, scientists would expect to see the adaptations for that task in its physical characteristics, known as its morphology.
For example, a deer’s great sense of smell is made possible by a long snout which is clearly visible in the shape of its skull.
Likewise, when it comes to dog breeds, you might think that specialisations like biting or hunting should also be reflected in their morphology.
However, Dr Waldrop and her co-authors suggest that this is not the case.
Dr Waldrop says: ‘We have assumed that these dogs look different because they are structurally specialized at these tasks, but our study shows that, at least for their skulls, they are not specialized for tasks that involve the skull, such as biting tasks and scent work.’
The researchers looked at 117 skulls from 40 domestic dog breeds and 18 wild relatives like wolves and foxes. They founnd that skulls from dogs bred to bite like a German Shepherd (right) were no different from the skulls of other dogs
When the researchers looked at skulls from American Bulldogs, German Shepherds, and Boxers they didn’t find any features that would give them extra bite force or allow them to ‘lock’ their jaws.
By analysing the mechanics of the skull’s shape, the researchers also calculated the ‘bite force quotient’, a measure of how strong an animal’s bite is relative to its body weight.
This revealed that dogs considered to have strong bites aren’t any better at biting than any other breed of their size.
In reality, the skulls of dogs bred for biting are almost exactly the same as dogs bred for other tasks like herding, pest control, and companionship.
Dr Waldrop says: ‘There are many news stories about dogs attacking people badly and often there are specific breeds that are targets of this reporting, such as pit bulls.
‘Some people claim that these dogs will bite harder than other dogs of the same size, or they have special features like “locking jaws” that make them especially dangerous to people. Our study shows that this is simply not true.’
Similarly, the skulls of dogs bred for scent work didn’t have any physical features that would help with this task.
The only group of dogs that do have distinct skull shapes are the so-called ‘brachycephalic breeds’ which include French bulldogs.
This graph shows how similar the skulls of different dog breeds actually are. Most dogs, uncluding working dogs known for their bite strength share very similar physical characteristics
These dogs have been bred to have exceptionally short noses and flat faces for purely aesthetic reasons and so deviate strongly from both domestic dogs and their wild ancestors.
However, all domestic dogs are quite distinct from wild canids like wolves and foxes.
The researchers suggest this is because their wild counterparts have skulls that better fit their biological needs rather than human preferences.
This therefore suggests that working dogs have been chosen more for their physical appearance and personality than any real physiological characteristics.
The researchers point out that this could have big implications for areas like law enforcement as it implies behavioural traits and individual personality could be more important than finding a specific breed when choosing working dogs.
However, just because XL Bullies don’t physically bite any harder, that does not mean they aren’t more dangerous than other dog breeds.
Dog behaviourist Stan Rawlinson previously told MailOnline that the XL Bully was ‘very, very reactive’.
Mr Rawlinson added: ‘I wouldn’t go near one. I’ve been around all sorts of dogs, even the most dangerous. But these XL Bully dogs are very reactive. They’re like the old Roman dogs of war that attacked Britain and helped forge an empire across the continent.’
None of the skulls studied had any features which would make them particularly dangerous or give them extra bite strength. This shows that the idea that XL Bullies can ‘lock’ their jaws is a myth
XL Bullies are among the five breeds deemed dangerous enough to ban in the UK; alongside the Pit bull terrier, Japanese Tosa, Dogo Argentino, and Fila Braziliero.
The previous conservative Government, which introduced the ban in 2023, said that XL Bullies had been ‘disproportionately involved’ in deadly attacks since 2021.
There have been a number of cases in which XL Bullies have killed their owners including several fatal attacks on children.
Two in four deadly dog attacks in the UK in 2021 involved the XL Bully breed – rising to six in ten in 2022, including high-profile maulings of children Jack Lis, ten, and Bella-Rae Birch, who was just 17 months.
Despite the prohibition of the Pit bull terrier, Japanese Tosa, Dogo Argentino, Fila Braziliero, and the XL Bully, dog bites have increased by 154 per cent in the past 20 years.
What’s more, between 1989 and 2017, 48 people – including 20 children – died in dog-related incidents.
However, of the 62 dogs involved, the overwhelming majority (53) were dog breeds not on the prohibited list.
