MISSISSIPPI STATE -- If the adorable puppy in the window of the pet store is an aggressive breed, prospective owners should think twice before taking it home.

Dr. Richard Hopper, extension leader of veterinary medicine at Mississippi State University, said genetics and environment contribute to a dog's aggressive nature.

"Some dogs have a greater tendency towards aggression than others, but aggression usually is promoted or worsened by the dog's environment and experiences," Hopper said.

Traditionally, German Shepherds, Rottweilers, Doberman Pincers and pit bulls are among the more aggressive dogs while collies and retrievers are considered among the most docile. However, cocker spaniels and poodles lead the breeds in the times they bite.

In choosing a dog, owners need to consider who the dog will live with, such as children, and where they live.

"Dogs are social animals and isolation or boredom sometimes make aggressive dogs more aggressive," Hopper said. "Penning dogs so they don't get enough exercise also seems to increase aggression."

Sudden movements, such as a child riding a bicycle past a dog, may trigger the dog's hunting instincts causing them to bite. The strong bond dogs form with owners can cause them to become overly protective. Dogs have attacked children in play if one tackles the dog's owner and the dog perceives it as a threat.

Other dogs become territorial of their yard or house. On walks, a dog may be friendly, but once at home, some become aggressive to the same people previously tolerated. Some dogs tolerate very little before they become aggressive.

"Owners have to realize that dogs have these instincts and should take preventative measures to make sure that no one is hurt and the dog is not allowed to be aggressive," Hopper said.

Hopper said some experts think dogs don't regard small children as they regard adults. To prevent trouble, dogs should be taught their position at the bottom of the family social ladder. Children should take part in the dog's training and discipline to enforce their authority over the dog.

In many cases, neutering the dog or using hormone therapy can suppress aggressive behavior. Other times, dogs can be simply kept away from situations which cause aggressiveness.

But sometimes dogs do attack and bite people. To prevent this, Hopper recommended never challenging an aggressive animal.

"It's best to stand still because if you run, the hunting instinct will typically take over and they will chase you," Hopper said. "If the dog is afraid, don't reach your hand out to them, just slowly move away.

"If you know the dog's name, call it out," Hopper said. "Sometimes trained dogs will respond to commands."

But if a dog attacks, the victim should protect their face and neck, as dogs do the most damage there.

"Kick the dog hard and run," Hopper said. "You can also try to hit the dog on the nose to deter it from further attacks."