Dogs are heartwarmingly friendly. They lick us, jump on us, would probably buy us a house if they could. We love them for it – even if sometimes they're a little too overenthusiastic – but the reason behind why these animals are so hypersocially engaging has never been fully understood.
Now, a new study examining the genetic makeup and behavioural traits of dogs and wolves has found that humanity's best friend shares a chromosomal overlap with a human disorder called Williams-Beuren syndrome – and the similarity could help to explain dogs' unshakeable sociability.
"It was once thought that during domestication dogs had evolved an advanced form of social cognition that wolves lacked," explains animal scientist Monique Udell from Oregon State University.
"This new evidence would suggest that dogs instead have a genetic condition that can lead to an exaggerated motivation to seek social contact compared to wolves."
Williams-Beuren syndrome is a developmental disorder that affects people's facial features and causes a range of health problems including heart defects and abnormalities in the brain and nervous system.
But one of the hallmark psychological symptoms of the syndrome is hypersociability, characterised by a lack of social inhibition and displays of outgoing, friendly behaviour even toward strangers, combined with high empathy.
Udell and fellow researcher Bridgett vonHoldt, an evolutionary biologist from Princeton University, observed the parallels between Williams-Beuren syndrome's hypersociability and the behaviour of dogs, and wanted to know how closely the two might be linked at a genetic level.
"It was the remarkable similarity between the behavioural presentation of Williams-Beuren syndrome and the friendliness of domesticated dogs that suggested to us that there may be similarities in the genetic architecture of the two phenotypes," vonHoldt explains.
In a 2010 study, vonHoldt had previously observed a similarity between the gene variants responsible for the human syndrome – called the Williams-Beuren syndrome critical region (WBSCR) – and their apparent analogue in dog DNA.
To find out if these variants might actually be responsible for hypersocial behaviour in dogs, in the new study the researchers took 18 domesticated dogs and 10 human-socialised wolves, and ran them through a series of behaviour-based experiments involving both familiar and unfamiliar people to gauge their individual sociability.
Unsurprisingly, the dogs proved to be more sociable with humans than the wolves taking part in the exercises – but when the team sequenced the animals' genomes in the lab, they observed that variations in a region of chromosome 6 in the dogs' DNA aligned with how social the dogs were.
Specifically, the more genetic insertions (called transposons) in the WBSCR affecting a protein called GIF21 seems to be strongly associated with dogs' hypersociability – whereas if they have less of these disruptions, they're more aloof and wolf-like.
Interestingly, it's the deletion – not insertion – of genes in the human counterpart of dog chromosome 6 (human chromosome 7) that leads to Williams-Beuren syndrome in people.
The researchers don't fully understand what's going on here and acknowledge that the sample of animals used in the study was small, so we should be careful about drawing too many conclusions from the research as it stands.
But nonetheless, it's a pretty amazing step forward that tells us more about how some of the genetic underpinnings of social behaviour may operate, in both dogs and people – and which could help explain how dogs separated from wolves during evolution.
"We haven't found a 'social gene,' but rather an important [genetic] component that shapes animal personality and assisted the process of domesticating a wild wolf into a tame dog," vonHoldt explains.
Scientists have previously wondered whether dogs acquired their sociability after wolves were domesticated by humans – but the presence of at least some sociability variants in the wolves studied here seems to suggest that the capability for extreme friendliness may have lurked hidden in wild wolves all along.
Just don't let the wolves lick your face.
The findings are reported in Science Advances.