Nature vs. nurture

The “pit bull debate” is almost always played out as a polarized conflict between the “pit bull lovers” on one side, who claim that a dog’s behavior is all about the way it’s raised, and the “pit bull haters” on the other side, who claim that a dog’s behavior is entirely dictated by genetics.

Neither viewpoint is correct.

“To compare the relative importance of the two factors [nature and nurture] separately is analogous to asking whether hydrogen or oxygen is more important in the makeup of water.” —Steven R. Lindsay, Handbook of Applied Dog Behavior and Training, Volume One.

A dog’s behavior occurs due to a combination of both genetics and environment. This is also true of human beings, cats, horses, rats, and any other living being on the planet. It is this combination that makes each and every dog (or human, or any other living thing) a unique individual.

**My purpose on this page is to assist the bewildered with some easy-to-follow analogies and explanations.**
If you’re looking for serious scientific research, I highly recommend the following books:
Genetics and the Social Behavior of the Dog by John Paul Scott and John L. Fuller
Handbook of Applied Dog Behavior and Training (Volumes 1-3) by Steven R. Lindsay

Genetics and Temperament

All living things are born with a set of genetic blueprints. These genes control physical appearance and general temperament.

Indeed, temperament is genetically (biologically) determined—but temperament and behavior are not the same thing.

What exactly is temperament?

“Each individual—human or animal—is born with a definite tendency toward varying degrees of emotional reactivity in the direction of behavioral inhibition or excitability. . . . Clearly, genetic factors predispose dogs to exhibit certain inevitable behavioral strengths or weaknesses.” (Stephen R. Lindsay, Handbook of Applied Dog Behavior and Training, Volume 1)

The two things you should remember from this definition are:
1. Temperament is a trait possessed by an individual, not a group.
2. Temperament is a tendency or predisposition but not a definitive action.

What this means can be boiled down rather simply: Temperament sets the stage but does not write the play. Temperament is potential.

A dog’s genetics influence the possible behaviors which may be produced by the dog, much the way a dial on an oven displays the possible temperatures the oven could be set at.
Genetics limits potential behaviors. For instance, I cannot teach a dog to sing opera, because genetics makes this potential behavior impossible. In the same way, my kitchen oven’s maximum temperature is 500 degrees, whether I like it or not.
Genetics allows potential behaviors. Dogs may not be able to sing opera, but they have a wide range of barks, yelps, and whines that they can use to communicate. Genetics makes these noises possible and probable.

Temperament, a genetic component, defines the probability that a particular behavior will be displayed in a particular circumstance.

Theoretically speaking, each dog breed should have a certain temperament. To that end, responsible breeders try to “breed for temperament.” But it’s not as simple as it sounds! Unlike coat and eye colors, temperament isn’t dictated by one, two, or even a handful of genes. There’s no “shy” gene. There’s no “hyper” gene. Temperaments can vary significantly even between litter mates.

In the end, the idea that breeds have specific temperaments is wishful thinking. Even with a breed that is supposed to have a specific trait (e.g., all Labs are fond of water), there are still many individual dogs who do not meet the ideal temperament (e.g., some Labs do not like water). Temperaments that are described in breed standards are ideals, and the overwhelming majority of dogs fall short of the ideal.

“Biology and genetics define the limits of how and what an animal learns, whereas experience dictates the moment-to-moment direction of these behavioral changes.”—Steven R. Lindsay

Environment and Behavior

Temperament is not a guarantee of behavior. You could say that a person is “quick-tempered,” but if they existed in a vacuum, would they still be so? If nothing exists, what could cause a quick-tempered person to be angry? Similarly, a dog may have a friendly temperament, but that dog is friendly because it has people and dogs to act friendly towards; if it was the only living creature on the planet, would it still be friendly?

For behavior to occur, environment must come into play. A dog barks at the mailman, a person cries at a movie, and a horse gallops away. These behaviors (barking, crying, galloping) are all prompted by things that occur in the environment. If the mailman hadn’t walked by, the dog would be silent. If the movie was a comedy, the person might laugh instead of cry. The horse gallops because it has space to run. All living creatures’ voluntary actions are prompted by the environment—the surroundings and conditions in which they live.

A creature’s past environmental experiences may also influence current behavior. This is the fundamental basis by which canine trainers and behaviorists find their success. Because dogs, humans, and many other living creatures learn and adapt to their environment, behavior may change over time. A dog with a friendly temperament may still bite if it is abused enough. With proper training and treatment, a dog with a fearful temperament can learn not to cower at the sight of a broomstick. The temperament doesn’t change, but behavior can.

Example. My dog Felanie was born with a fearful temperament. She startled more easily than other puppies. She tended to be more fearful of new situations. In her early life, Fel’s fearful temperament was exacerbated by the abusive environment she lived in. Her environment prompted her to exhibit fear-based behaviors like slinking, darting, growling, and warning barks.

Felanie’s temperament would never change, but her environment and her behavior did change when her abusive owner left and she joined our family. Felanie received new, positive experiences in a loving household. She developed a new set of behaviors that were friendly and social. Her fear-based behaviors faded away.

However, until the day she passed away, Fel remained a generally shy and quiet dog. She would hang back, hesitate, and proceed more slowly, where other dogs might race forward. Part of this was due to the early abuse, but part of it was her temperament, her predisposition to be a bit more cautious. I was always mindful that Felanie needed special attention when something potentially scary was about to happen in her environment, like a noisy party or a thunderstorm. By managing her environment, I was able to control Felanie’s behavior as well.

All dogs have similar quirks related to their temperament, from the dog with separation anxiety to the social butterfly who can’t resist running across the street to play with the neighbor’s kids.

And all responsible dog owners adopt a variety of management techniques to alter their dog’s behavior and cope with their dog’s temperament, whether they realize it or not.

Aggression: Today’s battleground

“Used precisely, ‘aggression’ refers to fighting and means the act of initiating an attack.”—John Paul Scott, Aggression

The “pit bull problem” seems to center around whether aggression is inherent or learned. Aggression is a behavior; a complex behavior with many different possible causes, but a behavior nevertheless. We know that behavior is influenced by environment and experience.

John Paul Scott was a renowned scientific researcher who was interested in the interplay between genetics and behavior. He did experiments with mice to determine whether highly aggressive mice could be created through breeding. He came to this conclusion:

“The experiments with mice show us that aggression has to be learned. Defensive fighting can be stimulated by the pain of an attack, but aggression, in the strict sense of an unprovoked attack, can only be produced by training. . . . Heredity can enter into the picture only in such ways as lowering or raising the threshold of stimulation, or modifying the physical equipment for fighting. . . . In considering hereditary effects, we must always remember that the environmental situation is also important.”—John Paul Scott, Aggression

In other words, according to Scott, aggression is a learned behavior.

Further along these lines, some dogs have temperaments that are conducive to aggressive behavior. That is, certain temperaments increase the liklihood that a dog will exhibit aggression. A dog with a fearful temperament, for example, may progress along the line from mere growling to an outright bite more quickly than a less fearful dog in a similar situation. Scott understands the influence of genetics in this regard; this is why he writes that “heredity can enter into the picture only in such ways as lowering or raising the threshold of stimulation.” Temperament is the thing which raises or lowers that threshold and makes a dog more or less likely to react aggressively in a given situation.

We have all heard stories about dogs who were not trained to be aggressive, yet still attacked someone. Remember, however, that learning occurs all the time, not just when a dog is formally trained by its owner. Dogs learn life lessons from a variety of sources, including, but not limited to, the owner. For example, a dog’s play, in which two dogs pounce, growl, and tussle in a playful manner, is actually ritualized aggression. When dogs play, they are learning and practicing a kind of aggression.

Here’s a typical scenario to illustrate how an “untrained” dog can nevertheless learn to be aggressive.

Example. Fluffy has a somewhat fearful temperament. He’s timid and submissive around other dogs and people. Fluffy’s owner takes him back to the dog park several times a week. Although she thinks Fluffy is getting socialization, in truth Fluffy is totally overwhelmed by all the other dogs, and he spends a lot of time trying to avoid them.

One day at the dog park, another young dog decides to challenge Fluffy. Terrified, Fluffy defends himself. Fluffy’s owner lets the two dogs “work it out.” Perhaps she chuckles because it’s so “cute” to watch the two dogs “act so tough.” Perhaps she thinks that Fluffy will gain confidence by “sticking up for himself.” Most likely, she simply isn’t paying attention. Whatever the case, Fluffy’s owner doesn’t intervene. Finally, Fluffy desperately asserts himself and manages to get the other dog to back off. In Fluffy’s mind, defensive aggression was successful because it brought about the desired result.

One day, a much bigger dog starts playing with Fluffy, but he’s too rough and Fluffy starts getting scared. He doesn’t want to play anymore, but the big dog won’t leave him alone. Fluffy decides to use defensive aggression; he snarls, barks, and snaps at the big dog. The big dog is surprised and runs off to find a nicer playmate. Once again, Fluffy’s aggressive display was successful.

Now Fluffy knows how to get other dogs to go away. He just has to growl, maybe snap his teeth, and they leave. It usually works. But one day a puppy comes over to play with him, and the puppy doesn’t understand Fluffy’s growl. The puppy keeps pouncing on him, biting his ears and tail, and making him nervous. Fluffy gets more and more anxious. His growls and snaps don’t seem to be working.

Finally, Fluffy decides to take it to the next level. He bites down on the puppy’s face—hard. The puppy shrieks and struggles. People start shouting, and Fluffy’s owner runs over. She is screaming and she starts hitting Fluffy. Fluffy becomes even more terrified at the sudden quantity of noise. He drops the puppy and cowers in fear. Fluffy’s owner interprets his frightened cowering as a sign that “he knew he did something wrong.” But to Fluffy, the hard bite worked. The beastly little puppy went away, and in a few minutes Fluffy was safe and sound in his owner’s car.

Fluffy’s owner doesn’t take him back to the dog park for several weeks—much to his relief! After a while, though, Fluffy’s owner decides that the bite incident was a fluke. She makes up excuses for Fluffy: “the puppy provoked him” and “he knew he was bad, he won’t do it again.”

Unfortunately, fearful Fluffy has learned that an actual bite is much more effective than mere growling. If he bites, the other dogs will avoid him, and his owner will take him home! From the front seat of the car, Fluffy sees the other dogs at the park and his heart beats faster. He is nervous and anxious. He whines. His owner says, “Okay, okay, go play” and she opens the door.

Fluffy runs straight to the nearest dog and launches a preemptive strike. Don’t mess with me! Chomp! Much to Fluffy’s surprise, the strange dog doesn’t back down from this sudden attack. It bites back, and now Fluffy is really scared. His adrenaline starts flowing. Fluffy and the strange dog get into an all-out fight!

Fluffy’s owner and the strange dog’s owner both start shouting. Fluffy’s owner pulls back on Fluffy’s collar. Fluffy misinterprets her screams. To Fluffy, it seems like his owner is also scared of the other dog. Her hand on his collar makes it seem like she’s supporting him. Fluffy’s fears are confirmed, and he fights even more fiercely against his terrifying canine opponent.

“But I didn’t teach him to fight!” protests Fluffy’s owner as the vet stitches her dog up. And that’s true.

But Fluffy has learned to fight. Fluffy’s environment, including his learning experiences at the dog park and his naive owner’s actions (or inaction),  and his fearful disposition worked together to foster his aggressive behavior. To make matters worse, Fluffy’s owner hasn’t done anything to stop Fluffy from learning and practicing aggression.

Until Fluffy’s owner learns to manage her dog’s fears and control her dog’s environment, Fluffy will continue to attack other dogs.

Fluffy’s story demonstrates that aggressive behavior does not require training or abuse. Aggressive behavior is learned, but learning does not require formal training.

Aggressive behavior typically progresses along a line. It starts with very minor signs, such as growling and raised fur. If the dog is given more opportunities to rehearse aggression, the dog will learn, practice, and improve, even without direct training.

Owners, especially those who rarely interact with their dogs, may not even notice that the aggressive behavior is progressing until an animal or a person gets seriously injured. Dog attack researcher Karen Delise notes: “Many owners [of dogs that committed fatal attacks] expressed shock at the ‘sudden’ and deadly aggressiveness of a pet they believed they knew. But, in reality, most owners did not really know their dogs. The fact that 25% of these dogs lived their lives at the end of a chain, 17% were running loose and 3% were kenneled indicates that many of these dogs were not spending a lot of quality time with their owners.” (Fatal Dog Attacks: The Stories Behind the Statistics)

The remedies for aggressive behavior are beyond the scope of this page; I merely wish to clarify that aggression is not entirely dependent on either genetics or environment.

Regardless of whether or not a dog is temperamentally inclined toward undesirable behaviors like aggression, it is the owner that ultimately determines whether the dog actually has the opportunity to react aggressively and rehearse aggressive behavior.

Owners who are responsible and involved do not give their dog the opportunity to practice or escalate aggression! If an owner observes that their dog growls or lunges at other dogs, a responsible owner might employ a trainer or behavior counselor, who might recommend desensitization, controlled socialization, confidence-building, or other types of learning experiences. Or, the owner might decide to manage the behavior by restricting their dog’s access to other dogs. Remember, it takes two for aggression to occur: one to aggress and the other to receive the aggression. A dog cannot attack a victim that doesn’t exist.

By working to inhibit, reduce, or prevent aggressive behavior at the first signs of a problem, the responsible owner breaks the cycle of escalating aggression and significantly reduces the liklihood that their dog will ever have the opportunity to behave aggressively.

Dog owners cannot change a dog’s genetics or temperament, but they can strongly influence behavior by manipulating the dog’s environment and experiences. Dog owners are completely in control of the environment in which their dog lives. They decide where the dog spends its time and whether the dog interacts with other people or animals. They expose (or fail to expose) the dog to social situations and learning experiences. They teach (or fail to teach) the dog how to behave. When a dog attacks, the blame rests squarely on the owner’s shoulders for failing to manage the dog’s environment and behavior appropriately.


  • Genetics (nature) sets a dog’s physical appearance and temperament. Temperament influences the likelihood that a particular behavior will occur in a particular situation.
  • Each and every dog has an individual temperament.
  • Environment (nurture) includes the conditions in which a dog lives and the experiences the dog has.
  • Behavior occurs only after the interaction of genetics and environment.
  • Aggressive behavior requires environmental stimulation; there is no internal drive to aggress.
  • Dog owners cannot change genetics, but they have total control over the dog’s environment and learning experiences. Dog owners therefore have significant control over their dog’s behavior.

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