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Show caption The findings suggested that how aggressive a dog is may have little to do with genetics. Photograph: David Joel/Getty Images

Animal behaviour

Research shows high degree of variability between individual animals – with implications for owners

From sociable labradors to aggressive pitbulls, when it comes to canine behaviour there are no end of stereotypes. But research suggests such traits may have less to do with breed than previously thought.

Modern dog breeds began to emerge in the Victorian era and are often physically distinct – for example, great danes are huge and chihuahuas tiny. But it has often been thought breed can predict behaviour, too.

Now researchers say there’s little sign that’s the case.

Dr Elinor Karlsson of the University of Massachusetts Umass Chan medical school, a co-author of the study, said research revealed a huge diversity of behaviours within each breed.

“Even if the average is different, you’ve still got a really good chance of getting a dog that doesn’t match what people say that breed is supposed to be,” she said.

Writing in the journal Science, the US researchers report how they analysed survey responses relating to the physical traits and behaviour of 18,385 pet dogs, almost half of which were purebred, with genetic data analysed for 2,155 of them.

Analysis of the survey results for purebred dogs suggested about 9% of behavioural variation was explained by breed.

“For the most part, we didn’t see strong differences in breeds, but there are some [behaviours] that are connected to breed more than others,” said Karlsson.

While no behaviour was exclusive to one breed, howling was more common among beagles, while pitbulls and retrievers were more “human sociable”, or comfortable with strangers.

There were also some differences based on dogs’ ancestral functions. For example, herding breeds were, among other traits, more biddable.

But there was a high degree of variability between individuals, meaning it is difficult to predict a dog’s behaviour based on its breed.

To explore whether genetics explained the associations, the team analysed the behaviour of mutts that had different levels of ancestry from particular breeds. The results reveal some traits have a stronger genetic component than others.

Labrador retriever ancestry was associated with mutts who had few qualms about getting wet, yet such ancestry appeared to have no link to human sociability.

“We’d expect that if Labrador retrievers are genetically more human social, we should see that mutts with more Labrador retriever ancestry to be more human social,” said Karlsson.

While the team’s other analyses found human sociability is highly heritable, Karlsson noted the mutt results suggest the genetic variants involved do not appear to be more common in particular breeds. Instead, differences between breeds for this trait may be down to environmental influences, or even owners’ perceptions.

But not all behaviours were found to be heritable, including how easily a dog is provoked by a frightening trigger – a finding that suggests that how aggressive a dog is may have little to do with genetics.

The team says the study has implications for owners.

“They should pay much less attention to all the stories about what their dog’s breed ancestry says about their behaviour and personality, and pay attention to the dog sitting in front of them,” said Karlsson.

Daniel Mills, professor of veterinary behavioural medicine at the University of Lincoln, who was not involved in the work, said genetics can give insights into populations but often reveal far less about individuals.

Mills added that it was not surprising genetics played little role in canine aggression, and criticised breed-specific legislation.

“Potentially risky behaviours … are unlikely to be controlled by simple genetic mechanisms since animals have to make judgment calls based on the much wider environment and their developmental history,” he said.

The findings came as another study, published in Scientific Reports, revealed that different breeds have strikingly different life expectancies.

The analysis of 30,563 records of dog deaths in the UK, collected between 2016 and 2020, showed that while jack russell terriers have a life expectancy of 12.72 years at birth, flat-faced breeds tended to have shorter lives, with French bulldogs having a life expectancy at birth of just 4.53 years.

Such brachycephalic dogs are known to be prone to myriad health problems as a result of their extreme physical traits.

Justine Shotton, president of the British Veterinary Association, said the findings of lower life expectancy for flat-faced breeds was concerning: “While the study doesn’t prove a direct link between these breeds’ potential welfare issues and shorter length of life, the findings serve as a fresh reminder for prospective dog owners to choose a breed based on health, not looks.”

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