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Offensive Aggression:
This is also known as “Inter-male aggression” or “competitive aggression”. It involves animals competing for resources and opportunities to pass on their genes to the next generation. Please note that dogs do not compete for "dominance" - squabbles occur over specific resources and no mythical "pack leader" status is achieved during these conflicts. When male dogs reach adolescence their testosterone levels increase dramatically. Testosterone is the hormone of “stupidity”! It increases confidence (or foolhardiness) so that young dogs start to compete with other dogs for resources (food, shelter, access to bitches). Winning a challenge over a resource is a powerful learning experience (the emotional state afterwards is a positive one) so the more squabbles a dog wins, the more he will tend to challenge other dogs for stuff. Removing testosterone (castration) can can reduce this behaviour. However, when a young dog lacks confidence and shows aggression due to fear, he may actually benefit from keeping his testosterone! Castration is therefore not a cure-all for aggression. 

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Bitches do also engage in competitive aggression, but usually to a lesser extent than dogs when it comes to dogs that they meet outside of the home environment. Bitches that are situated between two males in utero (2M bitches) tend to have higher levels of testosterone and may be more “feisty”.

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Predatory Aggression:
Luckily most dogs only ever show predatory aggression towards small fluffy animals of other species (squirrels, rabbits and birds etc). However, some dogs that are not socialised with small dogs early on may mistake them for prey. A predatory attack on another dog is usually characterised by grabbing and shaking the small dog without much noise. The dog may even appear as if they are having fun. Attacks are often fatal. Occasionally something called “Predatory Drift” occurs where a big dog that is usually fine with small dogs grabs a small dog due to it limping or screaming suddenly (acting like prey). Very rarely small children may elicit predatory behaviour in some dogs - usually if the dog has not been socialised with children and doesn’t recognise them as human beings. Screaming and running are behaviours which tend to trigger this kind of attack.

Defensive Aggression
This type of aggression is simply the “fight” option of the survival system (other options are flight or appeasement). It arises from the dog perceiving a need to protect itself from a possible threat. This option may not be the dog’s first choice, but may be utilised when escape is not possible e.g. when the dog is on the lead - hence the large amount of dogs with on-leash aggression.

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When an animal uses any survival strategy successfully i.e. survives the encounter, the animal’s brain floods with dopamine (this is the “high” that people experience after sky-diving or bungee-jumping). This feeling is highly rewarding and creates a very powerful learning experience. As a result the animal is more likely to use that same strategy again in similar situations. This is how aggression becomes a learned behaviour and why many dogs use aggression to resolve situations (especially on-leash situations). Allowing a dog to “practise” aggressive behaviour turns it into a habit, so for this reason we must try to manage dogs as much as possible to prevent them from having the opportunity to rehearse this type of behaviour in inappropriate situations.

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In extreme cases (rarely) a dog can actually become addicted to aggression i.e. they deliberately seek out confrontation in order to obtain the survival “high” afterwards. This is more likely to occur if the dog has very little else in its life that is rewarding. (Human “adrenaline junkies” and also drug addicts are thought to have a fault in their internal reward system that prevents them deriving pleasure from ordinary activities that most of us enjoy on a daily basis.)

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Dogs usually give lots of warning signs when they are feeling threatened which gives us an opportunity to resolve the situation without it deteriorating to a point where the dog feels the need to bite. Such warning signs may be:

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1. Pulling back the ears flat against the head
2. Lowering body posture into a crouching position
3. Backing up when approached
4. Creeping around behind you
5. Teeth chattering
6. Overexposure of the whites of the eyes.
7. Staring, often from a side angle
8. Expressionless or emotionless face
9. Hackles raised
10. Freezing
11. Growling
12. Snarling

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Unfortunately many owners are encouraged to punish these warning signs with the result that the dog has no way of showing when they are unhappy. When a dog has no means to communicate their unease they are more likely to go straight into nipping or biting without warning - so called unpredictable aggression.

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Dogs also show many signals that they wish to avoid conflict. When a dog displays a lot of these behaviours it means that they are experiencing stress:

1. Licking of the lips:
2. Yawning:
3. Turning the head away/walking away:
4. Sitting/lying down:
5. Sniffing the ground:
6. Walking in an arc when passing a person or dog:
7. Separating people/dogs:
8. Lifting of one paw (instinctively and not as a result of a cue):

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How to react to signs of stress or aggression:
In contrast to what “reality TV” dog training programmes would have us believe, confronting and eliciting aggression from a dog that is in conflict and then suppressing the behaviour through force is NOT the way to handle aggression problems. Neither is “flooding” the dog with a fear-inducing stimulus until it magically “gets over it” a way to deal with stress or anxiety.

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The correct way to deal with fear and aggression is through gradual desensitization, counter conditioning (classically conditioning a positive association with the threatening stimulus) and in some cases removing whatever may be rewarding the behaviour and rewarding a more appropriate behaviour instead.

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So a general remedial programme for a dog that reacts fearfully or aggressively to a situation, dog or person would be as follows:
1. Remove the dog from the threatening situation
2. Determine at what distance or intensity the dog can handle the situation
3. Reintroduce the “threat” at this acceptable distance or intensity
4. Pair the threat with something the dog likes (favourite food or toy) i.e. dog only gets that nice thing in the presence of the “threat”.
5. Slowly increase the proximity or intensity of the threat
6. Begin teaching a more appropriate behaviour in the presence of the threat e.g. sit and face owner, rather than lunge and bark

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A programme of this nature may take days, weeks or months to carry out, depending on the dog and the level of fear or aggression. There are no quick fixes in real life!

Bibliography:
1. Jean Donaldson, Oh Behave: Dogs from Premack to Pinker, Dogwise 2008
2. Panksepp, J, Affective Neuroscience, Oxford University Press, 1998
3. Le Doux, J, The Emotional Brain, Pheonix, 1999

4. O’ Heare, J, Aggressive Behaviour in Dogs: A Comprehensive Technical Manual for Professionals, DogPsych Publishing, 2007