Picking a breed of dog is usually about more than just looks. If you want a smart and playful pup, some would say a collie is your best choice. Whereas if you're looking for an outgoing friend for the whole family, a labrador might top your list.

Dog breeds have long been defined by certain behaviors and temperaments, but strangely enough, a new genetic study suggests breed alone is a poor predictor of canine behavior.

Searching the genomes of 2,155 dogs – encompassing 78 purebred breeds, along with mutts of mixed ancestry – researchers found very few genetic variants that could explain common dog behaviors.

These behavioral traits were identified from more than 18,000 survey responses from purebred dog owners.

In the end, the authors identified 11 spots in the dog genome that are strongly associated with behavioral traits, like how well a dog follows directions or how much they howl. Yet none of these were specific to the dog's breed.

In fact, breed could explain only 9 percent of the behavioral variation identified between individual dogs, and no behavioral trait was exclusive to just one dog breed.

The age and sex of a dog were actually stronger predictors of their behavior.

"The majority of behaviors that we think of as characteristics of specific modern dog breeds have most likely come about from thousands of years of evolution from wolf to wild canine to domesticated dog, and finally to modern breeds," says Elinor Karlsson, who studies comparative genomics at the University of Massachusetts.

"These heritable traits predate our concept of modern dog breeds by thousands of years."

Most breeds of dog you'll run into today have only been recognized as pedigrees within the past century or two, selected for aesthetic or physical ideals. Before that, pups were picked based on predictions of how well they'd hunt, guard, or herd.

Complex traits like behavior, which arise from many small genes interacting with one another and the environment, can certainly be inherited from one dog generation to the next, but modern pet owners might not have had enough time to really make an impact on the breeds we know today. At least, not in comparison to the contributions of our ancestors.

Karlsson and her colleagues were only able to find subtle genetic differences in dog behavior from breed to breed.

When you consider that more than half of all 'purebred' dogs in the United States have ancestries from more than one breed, the differences only grow subtler.

In the current genomic study, having a border collie ancestry did seem to have a genetic effect on a mutt's reported biddability, or their ability to follow human direction.

Yet there was no significant effect observed between Labrador retriever ancestry and human sociability.

In other words, labrador ancestry in a mutt didn't seem to make it any more sociable with humans, despite owners of purebred labradors reporting this as a key trait of the breed.

If the authors are right, and our assumptions about breed behavior are overstated, then national policies that ban certain 'aggressive' dog breeds might be unfounded. The same goes for insurance policies that refuse to cover breeds like pit bulls.

Karlsson's research is some of the first to examine the genetics behind breed-based behavior in dogs, but past studies have also found that variations in dog behavior within a breed are almost equivalent to that between breeds.

More work is needed to tease apart the genetics behind dog behavior, but the new findings suggest modern breeders haven't had quite the impact on our pooches that we thought.

When a dog obeys your command or cuddles up with you on the couch, it might have more to do with your ancient ancestors than the work of modern breeders.

The study was published in Science.