Jim Gillies CAB | CDBC( Certified Dog Behaviour Consultant )

Jim Gillies CAB, CDBC is a Clinical Animal Behaviourist based in Glasgow with over a decade of experience across a wide range of canine behaviour issues. He is an APBC Full Member, ABTC Registered, and IAABC Certified Dog Behaviour Consultant — and works across clinical consultations, veterinary collaboration, and expert witness instruction. His practice is welfare-led and evidence-based throughout. Jim runs CBT Dog Behaviour & Training and shares behaviour insights through his blog and podcast.

Aggression in dogs is neither purely genetic nor purely learned — it emerges from the interaction between inherited predispositions and life experience. Genetics set the template for sensitivity, arousal threshold, and behavioural tendencies. Learning, environment, and individual experience shape how those predispositions express in real-world behaviour. Effective behaviour work has to address both. This guide explains what the science currently tells us about the heritability of aggression, what role early experience plays, and what this means in practice for owners and behaviour professionals.

Last updated: April 2026

Why This Question Matters

The “is it genetic or is it learned” question is rarely just academic for the people asking it. Owners want to know whether their dog’s behaviour is something they caused, something they inherited, or something they can change. Behaviour professionals need to know which factors are realistically modifiable and which are not. Breeders, vets, and rescue staff need accurate information to make ethical decisions.

The honest answer — that it is always both — sounds like a hedge but is not. Behaviour science has moved well beyond the binary. The useful question is not which one but how much of each, and where can intervention realistically work?

What Genetics Actually Does

Genetics shapes the baseline equipment a dog is born with. Twin studies in humans, behavioural genetics work in laboratory species, and an expanding body of canine behavioural genetics research all point to a meaningful heritable component for several behavioural traits.

What is heritable in dogs:

• Sensitivity to stimuli — how readily a dog notices and reacts to environmental change
• Arousal threshold — how easily a dog moves into a heightened state
• Tendency toward fear or boldness — baseline confidence in novel situations
• Predatory motor patterns — eye-stalk-chase-grab-bite-kill-dissect-consume sequences seen in many working breeds
• General activity level and exercise need
• Sociability tendencies with people and other dogs

What is not heritable in any direct way is “aggression” as a discrete trait. There is no aggression gene. What is heritable is the combination of underlying tendencies that, in certain environments and with certain learning histories, can express as aggressive behaviour.

Some breeds do have higher reported rates of aggressive behaviour in research surveys (Duffy et al., 2008). This reflects the historical selection pressures shaping each breed’s typical behavioural profile, but it does not mean every individual of that breed will be aggressive. Within-breed variation is large. A nervous Labrador and a sociable Belgian Malinois are both common. Breed gives a probability, not a destiny.

What Learning and Environment Do

If genetics provides the template, learning and environment write onto it. The same genetically sensitive puppy raised in two different households can grow into two very different adult dogs.

Key environmental and experiential influences include:

The early sensitive period. Roughly weeks 3 to 12 — sometimes extended to 16 weeks — is when puppies are most receptive to forming positive or negative associations with the people, animals, environments, and handling they will encounter in adult life. Limited or poorly matched socialisation in this window has lasting effects on adult behaviour.

Learning history. Every interaction the dog has with a particular trigger contributes to how they respond next time. Aggression that worked — that made the trigger move away, or stopped a stranger reaching for them — gets reinforced. Learning is not separate from genetics; it interacts with it. A genetically sensitive dog forms strong fear associations more quickly than a genetically robust one.

Pain and health. An often overlooked environmental factor. Dogs in chronic discomfort show lowered tolerance for environmental triggers and increased rates of aggressive behaviour (Mills et al., 2020). Pain does not “cause” aggression in a genetic sense, but it is one of the most modifiable factors clinical behaviourists encounter.

Adolescence. A second window of behavioural sensitivity, typically between six and eighteen months. Fear responses can re-emerge or strengthen during this period, even in dogs who appeared confident as puppies. Adolescent reactivity is not always a “training problem” — it is often developmentally normal, and how it is handled shapes what stays.

Daily environment and stress load. Chronic over-arousal, insufficient rest, unpredictable routines, and high environmental stress all lower a dog’s threshold for reactive behaviour. None of this is genetic, all of it is modifiable.

The Interaction: Where Genes and Experience Meet

The most useful framing in modern behaviour practice is that genes set probabilities and experience determines whether those probabilities express. A dog can be genetically predisposed to be sensitive without ever showing aggression, given the right environment. Another with the same predisposition, raised differently, may present with significant behaviour problems by adolescence.

This is where the LEGS framework — developed by applied ethologist Kim Brophey in Meet Your Dog (2018) — becomes useful. LEGS prompts us to consider four influences on every behaviour: Learning history, Environment, Genetics, and Self (the dog’s internal state, including health and pain). The genetic-or-learned question is fundamentally a question about LEGS: behaviour is shaped by all four, and isolating any single factor as the cause is rarely accurate.

Epigenetics adds another layer. Environmental factors — chronic stress in a pregnant dam, early maternal care, prolonged stress in a young dog — can alter how genes are expressed without changing the underlying DNA. This is one of the mechanisms by which “nurture” influences “nature” at a biological level.

In Clinical Practice: A Multi-Factorial View

In my own clinical work, the cases that progress fastest are the ones where the owner is helped to see all the factors at play, not just the most visible one. Aggressive behaviour very rarely has a single cause, and treating it as if it does — whether that cause is “the breed” or “bad training” — leads to incomplete plans and disappointing outcomes.

One case I worked through recently illustrates this well. A high-drive working-line crossbreed presented with rest-related defensive behaviour — snapping when disturbed while resting after activity. On the surface, this could have been labelled “aggression” and addressed with generic training. A proper functional analysis revealed something more complex: genetic factors (high-drive breed combination requiring significant rest as well as exercise), environmental factors (insufficient structured rest in daily routine), learning history (snapping had successfully ended disturbance in the past), and a self factor (a previous undiagnosed hormonal modulator influencing baseline reactivity).

Removing one factor — the hormonal one, through veterinary intervention — improved the baseline. But the learned defensive pattern persisted until the environmental and learning factors were also addressed. That is what the LEGS framework is for, and it is why “genetic or learned” is rarely a useful diagnostic question on its own.

What This Means for Owners

Three practical points follow from the genetics-meets-experience picture.

1. You are not entirely responsible for your dog’s aggression — and you are not powerless. Genetic factors exist, and they place real limits on what behaviour modification can achieve. But the modifiable factors — environment, learning, pain, stress load, the way reactions are handled — are where intervention realistically works. Owner action matters, even when it is not the original cause.

2. Breed is informative, not predictive. Knowing your dog’s breed history tells you what they were selected for and what tendencies might be in play. It does not tell you what your specific dog will do. Treat breed as a useful guide for understanding, not a verdict.

3. Early intervention is more effective than late intervention. Once aggressive behaviour has been rehearsed repeatedly, learning history makes it harder to change. This is not a counsel of despair for older dogs — significant change is still possible — but it is an argument for involving qualified help early rather than waiting.

When to Seek Professional Help

If your dog is showing aggressive behaviour that is escalating, biting, or significantly affecting daily life, the appropriate route is via a veterinary referral to a qualified Clinical Animal Behaviourist registered with one of the recognised UK or international bodies (ABTC, APBC, or IAABC). A formal Functional Behavioural Assessment will identify the contributing factors specific to your dog and inform a tailored, welfare-led plan.

Veterinary involvement matters because pain and underlying health conditions are commonly contributing factors that need ruling in or out before behaviour modification begins. Read more about what an FBA involves.

Frequently Asked Questions

Further Reading

• Functional Behavioural Assessment: A Clinical Behaviourist’s Guide
• Rage Syndrome in Dogs
• Understanding Fear Aggression in Dogs
• Trigger Stacking in Dogs
• Kim Brophey: Family Dog Mediation
• Association of Pet Behaviour Counsellors (APBC)

References

• Brophey, K. (2018). Meet Your Dog: The Game-Changing Guide to Understanding Your Dog’s Behavior. Chronicle Books.
• Duffy, D. L., Hsu, Y., & Serpell, J. A. (2008). Breed differences in canine aggression. Applied Animal Behaviour Science, 114(3–4), 441–460.
• MacLean, E. L., et al. (2019). Highly heritable and functionally relevant breed differences in dog behaviour. Proceedings of the Royal Society B, 286(1912).
• Mills, D. S., et al. (2020). Pain and Problem Behavior in Cats and Dogs. Animals, 10(2), 318.
• Robinson, G. E., Fernald, R. D., & Clayton, D. F. (2008). Genes and Social Behavior. Science, 322(5903), 896–900.