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Canine Aggression Part 2: Nature vs Nurture

The following is an excerpt from my final thesis written for my Canine Behaviour Professional Diploma.


Nature vs Nurture


Is our dog’s personality, or temperament, set in stone or do we have the ability to impact it based on the environment in which we raise them? Are dogs who have been labelled ‘aggressive’ doomed to have aggressive puppies? If you bring home a young dog who begins to display aggressive behaviours is there any way that you can help them or is that behaviour ingrained and destined to always be at risk of appearing in when the conditions are just so? There has been debate in the past as to whether our dogs are influenced more by nature (their genetics) or nurture (their experiences), however, it is more widely accepted today that both play a role.


Dogs are certainly influenced by their genetics. Puppies inherit 50% of their genes from their mother, and 50% of their genes from their father. Genes are what dictate our behaviour and make up DNA. Our DNA makes up our body’s genome which has two parts: the genotype that cannot be changed, and the phenotype which can be influenced by the environment. The epigenome dictates which genes need to be used at which time and this is an innate decision that is based on the environment. Studies have shown it is possible to selectively breed fearful generations of mice, and that puppies born to mothers who experienced stress, fear and minimal resources during pregnancy have a higher likelihood of showing fearful behaviour as they grow. Fearful parents may pass on ancestral genes to their puppies that increase fearful behaviour if the environment dictates that that behaviour would be necessary for survival. We can also see the impact of genetics in certain breeds of dogs who, across the board, demonstrate similar characteristics and abilities that have not been taught. Border collies for example, are well-known for their ability to detect the most subtle of movements at far distances and have a natural ‘herding’ ability even if bred from a line of non-working parents.


If nurture were not a factor impacting a dog’s personality, then there really would not be any need for dog behaviourists who work to modify the behaviour of dogs who are experiencing struggles with fear, anxiety or reactivity. Dr. Jacqui Neilson writes,


“How genes exert their influence on behavior is not a simple situation, such as gene X makes a dog fearful. Instead, the genes encode for the production of enzymes and proteins that make anatomic structures and physiological processes that shape behavior. During this process different environmental things may influence their development such as temperature, experience and nutrients. Therefore, genes and experience are inextricably bound together in the development of a behavior.”


The environment in which a dog is raised, the level of enrichment they receive, life history, owner's nature and characteristics, and the methods used for training can all have a positive or negative impact on a dog’s personality. The use of aversive training methods have been shown to make dogs more reactive than they might normally be. Playing with a dog has shown to increase their trainability. Games-based concept training is based in game play with dogs and we are able to increase concepts such as optimism, confidence, tolerance of frustration and grit (amongst others) in our dog’s brain over time. We can use classical conditioning and desensitisation to help dogs with fears make positive associations and cope better with their environment. There is also evidence that shows the importance of providing young puppies with proper exposure to environmental stimuli during their first few weeks of life. Dogs learn from other dogs in the household – how to play, what to be afraid of, what not to be afraid of…my young dog learned how to pick up and throw her treat ball from my older dog. I think everyone has seen evidence in their own dogs in one way or another of how important nurture is in shaping their personality. If it were not possible for dogs to grow past the limits of what their genes initially dictate, many people would find themselves living with dogs struggling with fear, aggression, anxiety and all sorts of related behavioural issues, with no way to help them.


Every dog is an individual. We cannot think that every dog belonging to a specific breed group will have the same characteristics, nor can we ignore the fact that sometimes, as much as we may be providing a healthy, stimulating, positive environment, we will end up with a dog who has some characteristics that we just cannot change completely. Nature and nurture both play a role in determining the personality of our dogs. By educating ourselves as to how both of these come into play as our dog ages, we can learn how to best work with our dog as an individual and help develop and grow a confident, happy temperament in them.






The Importance of Early Socialisation


There are a variety of things that may contribute to reactive and aggressive behaviour developing in a dog. These can include lack of proper socialisation during critical periods in a dog’s development, traumatic events, genetics, and learned responses from other dogs or owners. If an owner does not recognize early signs, the behaviour can be reinforced unintentionally, thereby making it worse. Between the ages of 6-14 weeks old, puppies require exposure to a variety of novel experiences that are paired with positive experiences. Without this exposure, the tendency to grow up fearful when presented with new situations, people and/or objects increases. Traumatic events, such as being attacked by another dog, can result in reactive behaviour towards either all dogs, or dogs that specifically look like the ‘offender’. Puppies who come from a line of dogs who are in stressful situations (such as stray street dogs) and who themselves experience a high level of stress hormones may be genetically predisposed to reactive/fearful behaviour due to the higher level of hormones that they are exposed to while in utero. Reactive behaviour can also be learned by being exposed to other reactive dogs, or having an owner who displays tense, fearful behaviour in certain situations. A dog may pick up on these cues and therefore sense that there is reason to be afraid or defensive.


Good socialisation goes far beyond making sure that a puppy is exposed to a variety of people, objects and situations. It is important to ensure that all encounters with something novel are paired with positive experiences that will result in a positive memory. The quality of the exposure is more important than the quantity of experiences. Between the ages of 6 and 14 weeks old, a puppy is experiencing it’s critical socialisation period and it is during this time that it is crucial to make every attempt to limit negative experiences as they may end up creating a long-lasting negative impression that will impact their behaviour for the worse down the road. Dr. Tom Mitchell and Lauren Langman, in their “Optimism Rocks” e-book explain how while it is impossible to expose our dogs to everything they will ever encounter in their lives during these few short weeks, we can build up the concept of optimism and confidence by playing games that teach them that novelty in general is a good thing. All puppies will benefit from this sort of reinforcement, even at times outside of their critical socialisation period.


Positive socialisation can be hindered in many ways, some of which are due to owner behaviour and some are things that occur before a puppy even first ends up in it’s forever home. Puppies who are punished for showing fear behaviour, who are confined and not given the opportunity to have positive experiences and puppies who are neglected all may develop negative associations that can last their lifetime. If puppies are removed from their mother at too early of an age (less than 8 weeks old) there is the possibility of them having missed on learning important communication skills, developing strong enough self-confidence and problem-solving skills and showing difficulty forming new relationships. The earlier the puppy is removed from its mother the more likely it is to develop destructive behaviour, possessiveness, fear on walks, attention seeking behaviour, noise reactivity and excessive barking as a behaviour. A final thing that can hinder positive socialisation in a puppy is the way that it is treated at home during its first few days. A new puppy needs encouragement, guidance, support, and time to adjust. Being forced into too many new situations too quickly can have negative results.


There are natural stages of fear development that puppies experience and during these times they are very impressionable. It is important to be aware of when these periods are so that negative experiences can be minimized. The first fear imprint stage occurs between 8 and 11 weeks of age. Traumatic events during this time frame can have permanent effects. Fear can be generalised to include all the sense that were experienced at the time, so while it might be that a puppy was frightened by fireworks (the sound), if there was a particular smell that was present (maybe BBQ smoke) it is possible that that smell could become a trigger for a fear response independent of the firework noise. Physical trauma or psychological distress experienced during this time can result in avoidance behaviours. The second fear imprint stage occurs anywhere from 6 to 14 months (quite a large window of time!). As a puppy matures, they develop different senses and a new sense of self-awareness that can contribute to ups and downs in their behaviour. Support, guidance and encouragement are needed during this time to prevent their survival instinct from taking over resulting in them running from scary situations. Building confidence and optimism during this time is crucial.

Social Deprivation and Social Regression


Canine Social Deprivation Syndrome results from a stressful prenatal or neonatal environment, insufficient early socialization, or a particularly traumatic environmental event in a dog’s life and can be a contributing factor in the display of aggressive behaviours as a dog ages. Social Deprivation Syndrome will occur when the social needs of a dog are not met, especially in the crucial socialisation period between approximately 4 and 12 weeks of age. This is when the brain and nervous system are developing, the capacity for learning develops and positive experiences are crucial in contributing to the development of a healthy and well-balanced dog. Dogs suffering from this syndrome may be more likely to display aggression towards other dogs and people as they age if interventions and support are not put in place.


Puppies who have been removed from their mother at too early of an age, kept separate from their littermates, or who have not experienced contact with humans during these weeks all may find communicating with others more challenging. There can be serious and long-lasting consequences on the behavioural and physiological development of the dog. Social and non-social stimulation is important for normal puppy development…puppies learn how to interact with and play other dogs appropriately, they require exposure to sounds, textures, handling, and experiences that are presented in a positive way. At this early age, and for dogs of all ages really, the absence of one negative experience can far outweigh the effects of many positive ones – so ensuring that experiences with novelty are done gently and positively is important. Dogs who lack experiences, positive or negative, can be at risk of developing canine social deprivation syndrome as they get older.


A dog who is suffering from canine deprivation syndrome may show a variety of different behavioural signs. These can include aggression towards humans or others of their species and intense stress and fear reactions to other animals, people, objects and/or situations. We may see inappropriate play with other dogs and people, and some forms of barking, destructive behaviors, and house-soiling. Because the dog’s brain is developing during this early time, the psychological difficulties experienced by the dog can have a physical effect on its brain structure. Neural pathways that are formed at this time and then reinforced can be difficult to change as the dog ages. Puppies are often taught by their mother, and through play with their littermates, the ‘rules’ of good dog-dog communication and behaviour…dogs denied this learning experience may show inappropriate greeting behaviours when meeting dogs, rough play, the inability to pick up on cut-off signals from other dogs and possible fear-based behaviours such as barking, lunging, or shutting down upon seeing other dogs. Play fights between littermates can also help develop a puppy’s motor skills, so a dog who has not experienced this may show limitations in this area and appear ‘clumsy’.


These social deficits can negatively impact the life of a dog. If afraid of other dogs and people, the dog may be kept at home more often than not and so is denied chances to interact with the environment (which can lead to more fears and anxiety). Not being able to pick up on the social cues of other dogs can lead to fights and stressful encounters that could result in physical harm. Dogs living in fear of noises, of being left along, or in a home where there is conflict between themselves and another animal will experience higher levels of stress hormones in their body on a daily basis. This can lead to health issues such as digestion issues, sleep interruptions, skin irritations and further perpetuate the behavioural issues they already have. Many dogs ending up in shelters are between the ages of one and two years of age…a time when, for most people, the signs of inadequate socialisation really become apparent as a ‘problem’ that is too much to deal with. This can further add to the stress the dog is experiencing and make things even worse for them.


Ideally, no dog would experience canine social deprivation…mother dogs would be well taken care of and be in a stress-less environment, puppies would have litter mates and would learn necessary skills from them and their mother, and breeders would be well-informed as to how to provide a positive and enriching environment right up until the puppies are ready to go to their new homes. New homes would be ‘forever homes’ where owners are educated as to how to best expose their new dog to the world, and nothing negative would ever happen to the dog. However, that is not likely to happen for every dog any time soon.


Thankfully, the central nervous system remains plastic throughout life, and dogs who are suffering from canine social deprivation can be helped and new neural pathways in the brain that lead to different behavioural choices can be created with time and patience. We can help dogs work through their fears and anxieties towards people, other dogs, and situations. We can work to build their confidence when faced with novelty and help them by exposing them to new objects, experiences, and situations in a slow and positive way. By understanding social cues and how dogs communicate (both with humans and other animals), we can help them to have positive experiences with people and other well-balanced dogs.


On the flip side of things, because the central nervous system is plastic throughout life dogs who have been raised in the best way possible can experience social regression if placed in isolation as a growing or adult dog. When the ability to interact with others of its species, or with humans, is taken away a dog may lose some of its social capacity and we can see the same behaviours as seen in dogs with canine social deprivation syndrome begin to emerge.

Socialisation and exposure are not periods in a dog’s life that begin and end at set times and if done correctly will results in a balanced dog for life. Genetics, prenatal experiences, and early up-bringing are important in reducing canine social deprivation, but ensuring that a dog has continual exposure to situations, other animals and people in a positive way needs to happen in order to maintain a healthy and balanced state of mind and to make the likelihood of a dog feeling as though they need to resort to aggressive responses much less.

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