Rare Human Syndrome May Explain Why Dogs are So Friendly

 Dogs and people with Williams syndrome may both owe their sociable personalities to changes in the same genes.

When it comes to sheer friendliness, few humans can match the average dog. But people with Williams syndrome may come close, their unusual genetics granting them a puppyish zeal for social interaction. Now, scientists have found that extreme friendliness in both species may share common genetic roots.

A friendly condition

Williams syndrome, also known as Williams-Beuren syndrome, occurs when people are missing of a chunk of DNA containing about 27 genes. The syndrome affects about one in 10,000 people, and it is associated with a suite of mental and physical traits, including bubbly, extroverted personalities, a broad forehead, full cheeks, heart defects, intellectual disability and an affinity for music.

The first hint of a link between dogs and Williams syndrome came in 2010, when evolutionary biologist Bridgett vonHoldt and her colleagues examined DNA from 225 wolves and 912 dogs from 85 breeds. They were looking for parts of the genome that have been shaped by selection since dogs diverged from wolves.

One gene that popped out was WBSCR17, suggesting that it or other genes near it were important in dog evolution. This region of the genome is similar in dogs and humans, and the human version of WBSCR17 is located near the sequence that is deleted in people with Williams syndrome.

Doggie DNA

In the new study, vonHoldt, now an evolutionary biologist at Princeton University in New Jersey, and her colleagues took a closer look at the region surrounding WBSCR17. First, they tested the friendliness of 18 dogs and 10 wolves, all raised with regular attention from human caretakers. They measured how much time each dog or wolf spent within a 1-meter radius of a human, as well as how hard the animal worked to solve a puzzle box.

As expected, wolves spent less time near humans, and most worked equally hard to solve their puzzle box regardless of whether a human was present. In contrast, dogs tended to look at the human instead of the puzzle box, focusing on the puzzle only when left alone.

While dogs were more sociable than wolves on average, individuals varied, with some wolves acting more friendly and some dogs acting more aloof. When the researchers analyzed DNA from 16 of the dogs and eight of the wolves, the behavioral differences turned out to be correlated with variations in three genes -- the WBSCR17 gene highlighted in the 2010 study, and two additional genes from within the canine equivalent of the Williams syndrome region.

For each of these three genes, the researchers found multiple variants that differed in structural ways, such as whether or not they contained an extra sequence of DNA. Some gene variants were found mostly in the friendly dogs and wolves, while others were found more often in unfriendly animals.

While personality traits like friendliness are probably shaped by hundreds or thousands of genes, these three genes appeared to play a surprisingly large role in controlling social behavior, said vonHoldt.

"Some of these structural variants could explain a huge shift in a behavioral profile -- that you go from being a wolf-like, aloof creature, to something that's obsessed with a human," she said.

When the researchers examined those same three genes in 201 dogs from 13 breeds, they found similar patterns of genetic variation between breeds traditionally associated with friendly behavior, and breeds generally considered to be more standoffish.

Source: InsideScience