All domestic dogs belong to a single species that descended from wolves—despite vast differences in size,appearance,behavior and temperament among breeds.

While dogs first became domesticated tens of thousands of years ago, the breeds we know today are largely the result of selection for certain traits by humans over the past several hundred years.

"We have an enormous amount of diversity within the same species, and we can rarely observe such diversity in nature.

So it's a wonderful system to understand how evolution works within a short period of time."Evolutionary biologist László Garamszegi of the Institute of Ecology and Botany in Hungary.

He says that our playing with dogs is a key component of the human-canine bond.

But breeds vary in their degree of playfulness.

For example,a breed called the Vizsla is very playful.

"On the other hand,the Chihuahua doesn't like to play at all.

Of course,you can train a little bit, but the average level of playfulness will be always lower than in the Hungarian Vizsla." Garamszegi and his colleagues analyzed the playfulness of more than 89,000 purebred dogs across 132 breeds,from Pomeranians to Great Danes.

The dogs were all given a test measuring their degree of enthusiasm for a game of tug-of-war with people.