© J. Dehasse*¹, M Braem², S Schroll³

Introduction

There are many different classifications of aggressive behaviours in dogs that do not seem to agree with each other. Our intention is to review and analyze these classifications and to propose a clinically operative classification based on the integration of several existing ones.

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1.Methods

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2.Heuristics

What is the actual situation on paradigms, definitions and classifications on the different aggressive behaviours in dogs?

2.1.Paradigms of aggression

Definitions and classifications are shaped by history. Even before aggressive behaviors were described and classified, there was some arguing. Already since the early 1920s and 1930s, the instigators of aggression as an innate drive, an ‘appetite’ as Lorenz (1939, in Archer 1988) put it, and the followers of the aggression as a reaction to remove the animal from a particular set of aversive conditions (Craig, 1928, in Archer, 1988) have been discussing. If the motivation for aggression is a drive, it should appear with an increasing spontaneity in the absence of the performance of aggressive acts. Everyone who observes dogs has noticed this, but it is not frequent enough to establish it as a rule. The studies on the inheritance of aggression and clinical evidence show that there is a genetic basis for  the transmission of aggressive personality traits. On the other hand, psychoanalysis has put weight on the theory of frustration: any interference with an [expected] rewarding (pleasure-inducing) activity would produce a state of frustration, which then would lead to anger and aggression (Archer, 1988).

This philosophical foundation of ethology has influenced the process of classification. Moyer (1968) tried to put an end to the disagreements between Lorenz-Freud’s drive model, Dollard’s frustration-aggression model and Bandura-Walters’s learning theory model, “indicating that that the earlier classifications were not complete or not detailed enough” (Heymer, 1977). Moyer proposed “8 classes of aggression distinguished by a complex of contextual elements of which the eliciting stimulus is most important” (Greenberg). Numerous authors are using Moyer’s classification, but we think it just complicated matters. We will come back to Moyer’s classification later on.

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2.2.Defining and classifying behavior

There are two basic ways of defining behavior in ethology: definition by operation (or description, also called descriptive definition) and definition by consequences (or functional definition) (Morgan).

The preferred way is the descriptive definition. The functional definition adds the observer’s interpretation of the function of the animal’s so-called intent and is shaped by sociobiology models. The question underlying the sociobiology model of aggression is: How does the behavior contribute to the animal’s survival and fitness (reproductive success)? These models are often mainly focused on the individual and forget about the survival and fitness of the species. Socioecology (correlation between ethology and habitat) has produced a few theories that did influence the definitions. One of these hypotheses is the economic dependability, and another is the “game theory” in which the animal chooses the best strategy available under the current circumstances (Archer, 1988). For the behavior to be effective the animal needs to have several strategies to choose from or else it does not have any … choice!

The functional classification postulates the hypothesis of biological function, i.e. of adaptive fitness. The question now arises if the mechanism to achieve results good enough to fulfill the biological function may operate on principles logically unrelated to this function? (Archer 1988). For example does pursuit aggression have anything to do with predatory aggression, prey catching and prey eating? If it is unrelated to the aim and function, then the functional classification has no sense. It is to be hoped that many forms of behavior contain representations of a desired end-point (Archer, 1988). If this is true, then we have to seriously consider cognition in animals.

Social ethology, having extrapolated the analysis of dominance of the pecking order in chicken to more social animals, has produced the notion of dominance-aggression and extended it a bit hazardously to hierarchies. Controversies still exist about the definition of the dominant as the winner of the majority of fights and the dominant as the one who has gained access to most privileges. It is even actually shaping the world into different ideologies. As is still shown in the world of politics of ultra-liberalism: fighting may be of use for the society as a whole even if it destroys an individual. Is that biological wisdom or … nonsense?

We have to add the operational definition to these descriptive and functional definitions, i.e., “a definition that is restricted to a worker’s observation, measurement or manipulation procedures, or a combination of these procedures” [Immelmann and Beer 1989, in Barrows 2001]. Operational definitions are individual to each author, they cannot be standardized and, hence, will not be of interest to us here. One has to be aware of the fact that many authors bend/manipulate the existing definitions to their needs and then transform them into operational definitions, useless for the scientific community. 

Even if these methods of defining aggression are agreed on in Ethology, we will find other types of definitions when looking at the classifications of aggression. “Aversion-induced aggression”, for example, is a definition by cause (etiology) or trigger factor. As there is frequently more than one trigger factor, the observer may select the most apparent one in his hypothesis. Other classifications are contextual, for example “weaning aggression” (mild aggression toward offspring at weaning time).

And, up to now, we have only considered ethology. If we analyze other fields, such as behavioral medicine and psychology, we will find other classifications such as the genetically-determined “hard-wired” neural circuitry classification of David Adams (1979). Since his work is based on the rat’s and cat’s brain, extrapolating and applying it to dogs seems unsafe.

To make things more complicated, authors may use the same words to express totally different things, for example ‘parental aggression’ may mean aggression towards offspring (Wittenberger, 1981) or aggression to defend offspring (Archer, 1988) or may use different words to say the same thing.

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2.3.Models of classification

The way to define items has influenced the classification model. We found several classifications, for example by description, by function, by context, by (probable) cause.

We will try to group the designations of aggression found in the literature into these customary classifications. There will be problems. Several authors are using combined classifications, such as a descriptive-contextual-causal classification or a functional-causal-neural classification, etc. These complex classifications based on description, causality, context and neural circuitry – diagnoses - create an appeasing picture for the reader’s mind. It does not mean that they are pictures of reality or that they are validated, but they are theorized and modeled and often functioning. But, as Askew (1996) put it, “the concepts used to label the various problems are (…) scientifically speaking, an indefensible mixture of different levels or classes of concepts”. Askew thus proposed a new classification of aggression problems based on two basic categories: interspecific vs. intraspecific aggression, the last one being divided in intragroup vs. intergroup aggression. Each of these categories has several, sometimes common, definitions.

Moyer’s 8 items classification seems apparently simple. It is divided in predatory, intermale, fear-induced, irritable, territorial, maternal, instrumental and sex-related aggressions (1968). Moyer’s scheme, “based largely on laboratory studies” (Archer, 1988) can be criticized, one of the critics being that “the criteria for classifying the types of aggression were inconsistent” (Archer 1988). It mixes motivation, context, description, neural circuitry, etc. Pageat’s and Overall’s classifications are based on Moyer’s scheme.

Brain (1981, in Moyer 1988) is proposing a functional grouping in 5 categories: predation, infanticide, social conflict, parental defense and self-defensive aggression (in rodents). Archer (1988) adopts the same functional groupings. 

We have overviewed the following customary classifications of definitions of aggression:

• Descriptive (by operation) classification

• Functional (by consequences) classification

• Causal-motivational classification

• Affective class

• Cognitive class

• Sensorial class

• Space control class

• Social class

• Somatic class

• Contextual classification

• Neural classification

• Learning classification

• Complex and/or Diagnosis classification

• Therapeutic classification

3.The different classifications: overview

3.1.Descriptive classification

This classification is based on the description of the behavioral unit (sequence of acts).

Direct aggression (Wilson 1975, in Barrows 2000): “aggression in which animals confront one another with physical interaction.”

Fear-induced aggression (Heymer 1977): “aggression occurring only in cases where escape has been attempted but is not possible.” The ‘critical reaction’ (Hediger, 1950) where a cornered animal attacks a predator or conspecific falls into this category as well.

Intergroup aggression (Heymer, 1977): “fighting between various groups, populations or clans within the same species.”

Interfemale aggression (Heymer, 1977): “aggression elicited by a strange female of the same species and inhibited (in many cases) by the particular submissive behavior of that female.”

Intermale aggression (Heymer, 1977): “aggression elicited by a strange male of the same species and inhibited (in many cases) by the particular submissive behavior of that male.”

Intersexual aggression: aggression directed at unlike/different-sexed conspecifics

Interspecific aggression (Immelmann and Beer 1989, in Barrows 2000): “aggression that is frequently physically injurious between, or among, members of different species.”

Intragroup aggression (Heymer, 1977): “Aggression between individuals of the same group.”

Intrasexual aggression (Wittenberger 1981, in Barrows 2000): “aggression directed at like-sexed conspecifics of the same age class or reproductive class.”

Intraspecific aggression (Immelmann and Beer 1989, in Barrows 2000): “aggression that is often ritualized fighting between, or among, members of the same species.”

Mobile aggression (Beaver, 1994) : “mobile aggression is a reactive anomaly shown toward a perceived threat, as in dogs where the animal moves aggressively toward an approaching individual. (…)”  The author includes fear-aggression, maternal aggression and intrasexual aggression in this category. 

Pack response aggression (Beaver, 1994): “This is an aggressive behavior seen in some dog colonies and in multi-dog households in which the dogs that have been together a long time suddenly turn on one individual in their pack and kill it.”

Parent-offspring aggression (Greenberg): “disciplinary action against young.”

Parental aggression (Wittenberger 1981, in Barrows 2000): “aggression directed at progeny by a parent.”

Predatory aggression (Wilson 1975, in Barrows 2000): “a predator’s aggression towards its prey.”

Redirected aggression (Dewsbury 1978, Immelmann and Beer 1989, in Barrows 2000): “an animal’s action that it deflects from an object that arouses it toward a neutral (or substitute) object, e.g., a lower-ranking conspecific, a stone, or a clump of grass which it might pull.”

Sexual aggression (Greenberg): “elicited by stimuli that are related to sexual responses; directed against prospective mates.”

Weaning aggression (Wilson 1975, in Barrows 2000): “in some mammal species: aggression of parents that involves threatening and even gently attacking their own offspring at weaning time, when the young continue to beg for food beyond that age when it is necessary to do so.”

Xenophobic aggression (Southwick et al 1974, in Greenberg): “induced by strangers.”

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3.2.Functional classification

The classification uses the interpretation of the observer as to the function of the behavioral unit (sequence of acts). As there is frequently more than one function to a behavior unit, it may be the most apparent one or the most logical in the hypothesis (or beliefs) of the observer that will be selected. This is a modeled categorization.

Antipredatory aggression (Wilson, 1975, in Barrows, 2000): “aggression that is purely defensive behavior that can be escalated into a full-fledged attack on a predator (e.g. mobbing).”

Behavioral aggression (Southwick 1970, in Barrows 2000): “aggression that enables animals “to survive in competitive situations”.”

Competitive aggression towards human beings (Askew 1996): "Dominance aggression involves growling at and biting human family members in situations which either have a directly competitive element (...) or where the owner shows one of several kinds of behaviors or gestures towards the dog like touching it, or punishing it which are thought to provoke aggression because they resemble dominant dog behavior towards a subordinate dog."

Competitive Intraspecific aggression (Askew 1996): "Aggression between dogs in the same home": threatening behavior between two family dogs trying "to establish and maintain a dominant position in relation to the other". He counts "intermale" and "interfemale aggression" between two dogs in the same home as forms of competitive or dominance-related aggression. There are two possibilities for two dogs fighting over  the possession of some object...1) a form of dominance-related aggression...or 2) competitive, but not dominance-related aggression.

Defense of young (Askew 1996): It is not defined as "maternal aggression", because "males can show this kind of defensive reaction when a person or another animal in the family approaches puppies or a nest area."

Defensive aggression (Wittenberger 1981, in Barrows 2000): “an individual’s using aggression, often as a last resort, to defend itself or its offspring from predators.”

Distancing aggression (Dehasse 2002): “essentially proactive aggression against conspecifics or other animals (and humans) (particularly unknown or from other groups) having the apparent function to keep them out of the security distance of the aggressor dog.”

Dominance aggression (Wilson 1975, in Barrows 2000): “aggression involving displays and attacks mounted by dominant animals against fellow group members used primarily to prevent subordinates from performing actions for which the dominant animal claims priority.”

Ecological aggression (Southwick 1970, in Barrows 2000): “aggression that enables animals to invade and colonize new areas and exploit new habitats.”

Extragroup aggression (Askew 1996): "Extragroup aggression involves aggression either towards strange dogs or humans or towards humans or dogs outside of the family with whom the dog has had contact before and therefore recognizes as individuals". "The biological function of extragroup aggression is to safeguard and protect oneself, other group members , or critical resources needed for the group's survival against member of other groups of conspecifics - which may include both dogs and human beings...". It encompasses: group-defensive aggression, self-protective aggression, competitive aggression.

Group-defensive aggression (Askew 1996): This terminology “is used as a descriptive label for this category of aggression problem for two reasons": ...1) the behavior of the animal indicates that "the function of the behavior is to defend not only the individual itself but the group and its members as well" which distinguishes this type of aggression from "self-protective aggression…" 2) "such bold threatening and attacking behavior may often form the basis of cooperative, coordinated group defensive behavior..."

Material Protective aggression (Beaver, 1994): “the protection o guarding of objects such as food, toys, or facial tissue… [It] is often a part of competitive aggression and hormonal imbalance aggression, particularly in pseudopregnancy.”

Owner Protective aggression (Beaver, 1994): “form of affective aggression in which the animal protects its owner in a situation that the pet perceives as dangerous.”

Pain-elicited aggression (Askew 1996): "the dog is reacting to defend itself from what it may perceive as an immediate threat to its physical well-being".

Parental aggression (Archer 1988): “aggression whose function is to protect the offspring… [It] has often been referred to as ‘maternal aggression’ since it has only been studied experimentally in mammalian species where it is shown by pregnant and lactating females.”

Parental disciplinary aggression (Wilson 1975, in Barrows 2000): “In some mammal species: aggression used by parents; e.g., to keep offspring close at hand, urge them into motion, to break up fighting, and to terminate unwelcome suckling.”

Predatory aggression (Overall 1997): “Quiet aggression or behaviors congruent with subsequent predatory behavior (…), consistently exhibited in circumstances associated with predation (…).”

Protective aggression (Beaver, 1994): “[It] may be subdivided into territorial (protective) aggression, material (protective) aggression, and owner (protective) aggression. These involve guarding an area, a possession, or an owner from intrusion or attack.”

Puerperal aggression (Beaver, 1994):  “[It] is that shown by a female shortly after parturition. It has a sudden onset, is very aggressive, and is temporary.”

Self-protective aggression (Askew 1996): "The dog defends itself in a direct and obvious way". Aggression shown by dogs that "prefer to quietly avoid [strange dogs or humans] and only become aggressive "in self-defence", when approached too closely or threatened or attacked by a stranger". He considers the possibility of group-defensive aggression problems being a form of "fear aggression in the sense that they too involve the keeping away or driving away of what is basically a feared individual or at least a type of individual which is perceived by the dog as being threatening or potentially dangerous for some reason"...

Sex-related aggression (Beaver, 1994): “[It] is generally regarded as a normal behavior under hormonal and neurologic control. The nape bite is shown primarily by dogs […] when mounting. This grip is considered an inhibited bite, since its apparent purpose is not to leave a wound. In other forms of sex-related aggression, anoestrous females may react aggressively toward attempts to mount […]. An occasional complaint may indicate that an individual male is too rough [...].”

Sexual aggression (Wilson 1975, in Barrows 2000): “a male’s aggression involving threats and attacks directed toward a female that forces her into a more prolonged sexual alliance with him.”

Territorial aggression (Wilson 1975, in Barrows 2000): “an animal’s aggression used in defending its territory, often involving dramatic signaling behavior to repulse the intruders and with escalated fighting used as a last resort.”

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3.3.Causal- motivational classification

This classification sorts the aggressive behaviors by their hypothesized trigger (or eliciting)  factor, motivation or cause. This is a modeled categorization.

3.3.1        Affective-emotional class

Fear aggression (Overall 1997): see afterward. 

Frustration-induced aggression (Immelmann and Beer 1989, in Barrows 2000): “aggression due to frustration” (e.g. a switch from constant to partial reinforcement). 

Irritable aggression (Heymer, 1977): “aggression elicited by a wide range of stimuli and increased by frustration, deprivation, and pain.”

Irritation aggression (Pageat 1995): see afterward. 

3.3.2        Cognitive class

Pain aggression (Overall 1997): see afterward. [Anticipation of pain is a cognitive function]

Possessive aggression (Overall 1997): see afterward.  [Possession is a cognitive notion]

3.3.3        Psychological class

Psychological disturbance-related aggression (Overall, 1997): “aggressive behaviors that do not meet the criteria for specific aggressions.” [Causal, but very imprecise]

3.3.4        Sensorial class

Aversion-induced aggression (Immelmann & Beer 1989 in Barrows 2002): “an animal’s attack due to an aversive stimulus (e.g., pain), which may be directed at any bystander or inanimate object that is within reach.”

Irritation aggression (Pageat 1995): see afterward. 

Pain aggression (Overall 1997): see afterward. 

3.3.5        Space control class

Maternal aggression (Pageat 1995): see afterward. 

Territorial aggression (Pageat 1995): see afterward. 

Distancing aggression (Dehasse 2002): “essentially proactive aggression against conspecifics or other animals (and humans) (particularly unknown or from other groups) having the apparent function to keep them away from the security distance of the aggressor dog.”

3.3.6        Social class

Dominance aggression (Wilson 1975, in Barrows 2000): “aggression involving displays and attacks mounted by dominant animals against fellow group members used primarily to prevent subordinates from performing actions for which the dominant animal claims priority.”

Hierarchical aggression (Pageat 1995): see afterward. 

3.3.7        Somatic class

Atypical aggression (no author): unspecific aggressive behavioral sequence not classified elsewhere, and due to a somatic disorder, such as a metabolic (hypoglycemia, porto-systemic shunt), an endocrine, an inflammatory/infectious, a degenerative, a tumoral disorder, painful disorder, etc.

Hormonal imbalance aggression (Beaver, 1994): aggression that is “related to the imbalance of hormones within an animal… Estrous females have been known to increase the amount of their aggression toward females of the same species… Bitches in false pregnancy may guard objects. Even years after an ovario-hysterectomy, a bitch may continue to show cyclic tendencies toward aggression to other females at the same regularity as had occurred before the surgery.”

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3.4.Contextual classification

This category groups aggressive behaviors correlated to a specific repetitive context. It does not analyze the aggression in detail, but only the circumstances surrounding it. This approach is very imprecise because the protagonists may show different emotions that can trigger different kinds of affective aggressive behaviors. For example, a context of food competition between dogs may result in different aggressive sequences depending on if one or both dogs are starved or well-fed, this may be a survival fight for one dog or a hierarchical performance for the other dog.

Competitive aggression (Beaver, 1994): “a variation of dominance aggression where two animals compete for a favored food or location. When animals do not share equally, a solution to possession usually is decided by the dominant animal getting the prize of the competition”.

Food-related aggression (Overall 1997): see afterward. 

Hierarchical aggression (Pageat 1995): see afterward. 

Pain aggression (Overall 1997): see afterward. 

Play aggression (Overall 1997): see afterward. 

Playful aggression (Askew1996): "aggressive play of young dogs…"

Possessive aggression (Overall 1997): see afterward. 

Protective aggression (Overall 1997): see afterward. 

Territorial aggression (Overall 1997): see afterward. 

Weaning aggression (Wilson 1975, in Barrows 2000): “in some mammal species: aggression of parents that involves threatening and even gently attacking their own offspring at weaning time, when the young continue to beg for food beyond that age when it is necessary to do so.”

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3.5.Neural classification

This categorization is based on the experimental discoveries of genetically determined “hard-wired” neural circuitry organizations. Moyer (1968, in Heymer 1977) proposed different neural foci and circuitry in his classification and this was modified and broadened by Adams. This is a modeled categorization.

Defense aggression (Adams): “behavior under the control of defense motivational systems.” This subsumes the following behaviors: fear-induced aggression (Moyer), pain-induced irritable aggression (Moyer), part of maternal aggression (Moyer), and antipredatory aggression (Wilson).

Fear aggression (Pageat 1995): behavior under the control of the anterior hypothalamus and ventro-median nucleus.

Irritation aggression (Pageat 1995): behavior under the control of the ventro-medial hypothalamus, amygdaloidal nucleus and septum caudal nucleus. 

Offense aggression (Adams): “behavior under the control of an offense motivational system, activated by olfactory stimuli that characterize male conspecifics (in males), stimuli that characterize the opponent as unfamiliar, stimuli associated with competition for food or water when the animal is food- or water- deprived.” This subsumes the following behaviors: intermale aggression (Moyer 1968), territorial defense (Moyer) and aggression (Wilson 1975), irritable aggression in competitive interactions (Moyer), part of maternal aggression (Moyer), offensive threat (Flynn 1976), dominance aggression (Wilson 1975).

Predatory aggression (Pageat 1995): behavior under the control of the stimulation of the lateral hypothalamus.

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3.6.Learning classification

Learning affects most kinds of aggressive behaviors. Pain-induced aggression, for example, may be conditioned (classical conditioning) to the person who treats a painful disorder in a dog or to the place where the painful disorder is treated (or to any stimulus linked by classical conditioning to the painful episode).

Self-reinforcement and training can improve the competence in predatory aggression, or increase the operant level of any aggression. Nevertheless, these aggressive behaviors are not classified in this categorization.

Instrumental aggression (Heymer, 1977): “aggression based on any classification and consisting of an increase in the tendency for an organism to engage in aggressive behavior when that behavior has been reinforced in the past.”

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3.7.Complex and/or Diagnosis classification

Diagnoses of problem behaviors are not descriptions of behavioral events, but are hypotheses of useful units based on several signs. They do not imply an underlying mechanistic phenomenon (Overall, 1997, p.3-4). The diagnose classification pretends to be functional. In fact, it is essentially a contextual, non-causal, classification.

Moyer’s like complex classifications such as the descriptive-contextual-functional classification of Moyer has the same proposed useful objective.

We will put between brackets the probable customary classification.  

Dominance aggression (Overall 1997): “abnormal, inappropriate, out-of-context aggression consistently exhibited by dogs toward people under any circumstance involving passive or active control of the dog’s behavior or the dog’s access to the behavior.” [Contextual]

Fear aggression (Pageat 1995): same definition as Heymer’s Fear-induced aggression, with typical sequence without an intimidation phase or bite control. [Descriptive, contextual, causal-affective]

Fear aggression (Overall 1997): “aggression that consistently occurs concomitant with

behavioral and physiological signs of fear (…)”. [Contextual, causal-affective]

Food-related aggression (Overall 1997): aggression that consistently occurs in correlation with competition for food or access to food, even at long approach distances” (p. 105). [Contextual, causal]

Hierarchical aggression (Pageat 1995): “aggression shown between males or between females in the case of hierarchical competition; the sequence is divided into three typical phases: intimidation (threat), attack and appeasement.” This subsumes Moyer’s intermale and Interfemale aggressions. [Descriptive, contextual, functional]

Idiopathic aggression (Overall 1997): “aggression that occurs in an unpredictable, toggle-switch manner in contexts not associated with stimuli noted for any behavioral aggressive diagnosis and in the absence of any underlying causal physical or physiological condition”. [Descriptive, contextual]

Interdog aggression (Overall 1997): “consistent, volitional, proactive aggression that is not contextual given the social signals, threat circumstances, or responses received”. [Contextual]

Irritation aggression (Pageat 1995): “aggression having a typical sequence depending on the status of the dog in the hierarchy (dominant vs. submitted), and caused by pain, deprivation, frustration, persistence of body contact, etc.” [Descriptive, contextual, causal-sensorial]

Maternal aggression (Pageat 1995): “behavior triggered by the intrusion in the individual isolation field or group (pack) territory in the presence of puppies or affective analogue (in pseudocyesis), with a typical sequence of short intimidation, quick attack and return to the nest when the intruder has gone away”. [Descriptive, contextual, causal]

Maternal aggression (Overall 1997): “consistent aggression (…) directed toward puppies in the absence of pain, challenges, or threats to the mother by them.” [Contextual]

Mental lapse aggression syndrome (Beaver 1994) : « this is a type of aggression in which a dog that has been a good family pet turns aggressively on family members and friends. The behavior change is dramatic and usually consistent. … On EEG of anesthetized animals, this syndrome shows up as a low voltage-fast activity pattern…”.

Pain aggression (Overall 1997): “consistent aggressive behavior, in excess of that required to indicate concern and to effect restraint, demonstrated only in a context known or potentially associated with pain, but that may not be painful, itself.” [Contextual, causal-sensorial, causal-cognitive]

Play aggression (Overall 1997): “consistent aggression that occurs in contexts in which play behaviors (…) would normally occur.” [Contextual]

Possessive aggression (Overall 1997): “aggression that is consistently directed toward another individual who approaches or attempts to obtain a nonfood object or toy that the aggressor possesses or to which the aggressor control access”. [Contextual, causal-cognitive]

Predatory aggression (Pageat 1995): “description of two kinds of sequences depending on the size of prey” (small prey and large prey). [Descriptive, contextual]

Predatory aggression (Overall 1997): “Quiet aggression or behaviors congruent with subsequent predatory behavior (…), consistently exhibited in circumstances associated with predation (…).” [Contextual]

Protective aggression (Overall 1997): “aggression that is consistently demonstrated when an individual or class of individuals is approached by a third party in the absence of an actual, contextual threat from that third party.” [Contextual]

Psychological disturbance-related aggression (Overall, 1997): “aggressive behaviors that do not meet the criteria for specific aggressions.” [Causal-psychological]

Rage syndrome (Beaver 1994) : “general term … applied to unpredictable [and severe] aggression in certain breeds of dogs. (…) Histories of affected dogs suggest that genetic factors are involved, … Physiological changes often indicate a high degree of arousal. These can include disorientation, trembling, urination, and/or defecation. (…) In a few cases (…) dogs that fit the parameters of rage syndrome showed EEG changes characteristic of mental lapse aggression.”

Redirected aggression (Overall 1997): “aggression that is consistently directed toward a third party when the patient is thwarted or interrupted from exhibiting aggressive behaviors to the primary target.” [Descriptive]

Territorial aggression (Pageat 1995): “behavior triggered by the intrusion into the individual isolation field or group (pack) territory with specific sequences including intimidation, attack and possible contact if the intruder shows appeasing or submitting behaviors.” [Descriptive, contextual, causal-spatial]

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3.8.Therapeutic classification

One simple way to classify aggressive behaviors is to determine if they are sensitive (reduced or increased) to several medications or therapeutic approaches. We may even establish a scale from –10 to +10, “minus” being for an aggravation of the behavior, “positive” being for the reduction (or improvement) of the behavior. Such a scale has never been published and, most important, the experimental data are yet nowhere to be found. Such a study may start when scientists and veterinary behaviorists will agree on definitions and on a classification.

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4.Discussion on the overview

Ethologists have already been confusing descriptive and functional classifications ever since the beginning. Additionally, every author is bringing up new ways of classifying aggressive behaviors. A descriptive categorization is valuable and informative but may change from one species to another because the behavioral sequence may not be the same. A contextual categorization may be more valuable but may not be able to be generalized for different species either. A causal-motivational classification may be applied to different species even if the sequence of acts is different, but it is based on the author’s hypotheses and models and  it includes a kind of anthropomorphism.

Moyer’s (1968) classification seems to be of broad use. In veterinary behavioral medicine, both Pageat (1995) and Overall (1997) base their classifications on his. Overall says hers is a functional classification. It is functional in the sense of usefulness or practicality, but not in the sense of the function (or consequences for fitness or adaptation) of the behaviors. Moyer correlated his classification with neural zones and causal factors, sometimes with descriptions of the behavioral sequence (but nowhere can we find validation of this). Pageat restricts this classification by combining both intermale and interfemale aggression into a new class he names “hierarchical aggression”. Overall broadens the classification, importing or creating new classes such as “play aggression”, for example.

Adams also bases his work partly on Moyer’s classification, but with the aim to use the neural hypothesis to broaden his research on this subject with experimentations on rodents and cats. This might interesting intellectually, but, is there any sense in using this simplified classification (offense, defense, predatory aggressions) for clinical use? We do not think so.

Several appellations have changed meaning since they were put in use. Dominance aggression is one of these. Can we, in veterinary behavioral medicine, still use it with its original descriptive and functional meaning or should we use it with the much modified diagnose classification? We think it is better to drop it totally and invent new terminologies in clinical practice.  

“One of the most important insights the study of aggression leads to is the need for precise definition of causal, contextual variables and a valid way of associating these with the consequences of behavior. Aggression cannot be regarded as a unitary drive; precise definition shows that varying forms are discriminable and each must be then further investigated for possible specific variations in its neural and hormonal determinants. Further, each form of aggression may reflect ensembles of more or less open or closed genetic programs” (Greenberg).

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5.Proposal of a descriptive-contextual classification

5.1.Which classification?

How should one classify aggressive behavior? It will depend on the objectives. To depict the ethogram of dog aggressive behavior, one should use a descriptive classification. To treat aggressive behavior, one should use a disorder classification, in which aggressive behaviors are mere symptoms, or a symptomatic classification correlated with effective treatments. This ideal clinical classification does yet not exist.

The best classification should be a global one, using descriptive, contextual, functional, and causative details and particulars, including if possible neural circuitry and genetic analysis. We are far from this ideal situation. We may ask ourselves the question: does it exist? Even if there are totally different functions to aggression related to resource competition and reactions to danger, the authors seem to agree: “the mechanisms which underlie them have come to overlap (Archer, 1988).  The diversity of the phenotype may well be due to the combination of the action of only a few neural centers and mechanisms.

As the global description of a behavior should include a depiction of the sequence of acts, the analysis of context, postures, triggers (or eliciting factors) and multiple consequences, we think the descriptive-contextual method is better suited to the task at hand. The functional description could be derived (extrapolated) from the immediate and late consequences of the behavior and should establish if the behavior increases the fitness of the dog. But as many domestic dogs are neutered and live in artificial environments, part of the fitness evaluation (at least the reproductive fitness) of the behavior cannot be asserted anymore.

Next, we face a significant problem. The dog is socialized to - and cohabits with - more than just its species. That is at least a good reason not to compare it with a wolf. Is the aggressive behavior shown by the dog to people the very same as the one it shows to conspecifics? We have to hypothesize that it is based on the same behaviors but may be adapted and modified by learning processes and social interactions with people. Are there any study on the correlations between dog-dog behaviors and dog-people behaviors? We cannot find them; it seems everything is still in the domain of hypotheses.

A global descriptive-contextual classification does not imply that the behavior is normal, abnormal, physiological, pathological, or just problematic. It is just describing. This is a first step.

A second step may be to correlate descriptions and gather the correlated aggressive behaviors in clusters of aggressive behaviors, for example all space-managing aggression together if they are correlated.

The third step would be to find behavior therapies and/or medications that can influence these individual - or clusters of - aggressive behaviors. And so on until we can group different behaviors as symptoms in disorder descriptions.

We have to start somewhere and this proposal of classification is a start.

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5.2.Proactive and reactive modalities

As clinicians, we are interested to know if the aggressive behavior is dangerous to the environment or if it is manageable. An important criterion is the relative threatening motion of the dog and the target to each other (Dehasse, 2001). Is the dog moving toward the target or the target moving toward the dog and reaching it? In lots of situations the target makes a movement in the general direction of the dog crossing one of the security circles around him. This is not the important part in our definition. What matters is that the dog may be attacking a target that is not obviously threatening it. This is what we call proactive or pre-empting aggression. When the dog reacts to an obvious menace, makes no movement when threatening the approaching target, and then attacks when the target is at close quarters, we call it reactive aggression. No need to say that proactive aggressions are aggressions less easy to manage clinically. These are two modalities of sequences observed in each context, and they will modulate the sequence of the aggressive behavior.

This is only a description of part of the sequence of acts, it does by no mean signify that the proactive dog is not responding to an emotion or cognition of defense. In fact, the dog may always be defending something, its body, its space, its privileges, even a belief,… but we are not each time able to objectify it, even if we can model or theorize it.

There are biological reasons for the development of proactive aggression. There should be advantages for an animal to respond to potential danger before physical contact, i.e. when there is an intrusion in a spatial area (around the body or independent from the body), and to respond to stimuli, which predict noxious events (Archer, 1988). Proactive aggression should then be paired with a higher integrative cognition, perception and regulatory system: the animal should be able to recognize a potential threat, to compare it with previous experience, and to act quickly on this recognition but also to stop or modify its actions if new information on the target proved it was false.

Just saying that there exists a proactive aggression or proactive trait means also that there may exist some kind of determinism behind the scene. This is an inkling coming from clinical observation, more than from inheritance analysis, that several dogs in families may inherit a personality trait that makes them use more often impulsive and proactive than reactive behavioral strategies, and proactive aggression more often than flight, inhibition or appeasing strategies. 

In all categories, we may fond both proactive and reactive modalities, and sometimes a mix or a mosaic of them. Aggression has to be included in the ensemble of agonistic behaviors and analyzed relatively to other ways of coping with a threat such as flying, freezing or communicating (with the whole range of appeasing rituals). 

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5.3.Modulating factors

There are many modulating factors, which will modify the aggressive sequence. The proactive/reactive personality type is just one of them. A number of (psychopathological) factors can intervene alone or more often in combination to modify the behavioral sequence. We can classify these factors this way:

• Exogenous

• Psychological : attachment, detachment, deprivation, sensitization, generalization, ritualization, etc.

• biological: parasites, viruses and bacteria

• chemical:  medications and toxics

• Endogenous

•  psychological : mood, emotions, cognition, perceptions

• somatic disorders: dysendocriny, neurological disorders, painful disorders, etc.

• heredity

 One may build a table or diagram showing a few requisite characteristics (and their contrary) in a scale (for example from –10 to +10).

We put on the left a few criteria, which will reduce the danger of the aggressive behavior and to the right several criteria, which will increase the danger.  

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5.4.From mild to lethal aggressions

5.4.1.The typical sequence of aggressive behavior

The typical aggressive behavioral sequence observed in competition between conspecifics of the same group is divided in 4 phases: threat, attack, end, refractory. The attack may be prevented by appeasing rituals from the agonist/target and the attack ends with diverse submissive rituals of the agonist/target and is followed by a cessation of aggression (refractory phase) and temporary resolution of conflict.

5.4.2.Intra- or inter-group aggressions

Inside a group, cooperation and familiarity should reduce the risk of wound, hence one is expecting more control and ritualizing in the fights. Out of the group, in presence of conspecifics or individuals (humans) of other species the dog has been correctly socialized to, the same rules do not apply and fight may be more fierce and may result in invalidating wounds.

There are exceptions to the controlled ritualized intragroup aggression. We observe that there happens to be intragroup uncontrolled aggressions in case of individual endogenous parameters such as psychological/behavioral disorders for example overactivity, dyssocialisation, operant conditioning and mood changes.

5.4.3.Proximity and recognition of the agonist/target

The intensity of the aggressive reaction may depend on the proximity and the recognition of the target and cognition of the dog, basically it is increasing from known (member of the group) to unknown (not member of the group) to potentially … edible or on the contrary dangerous (predator).

The intensity of the aggressive reaction may depend on the proximity of the intruder/target (coming from the security distance to the critical distance) and on the recognition of the target and cognition of the dog, basically it is increasing from known (member of the group) to unknown (not member of the group) to potentially dangerous (as attested by (lack of) socialization) to really dangerous (as attested by past experience). The emotion and cognition of the dog is also important since reactive /protective aggression increase with the level of fear.

5.4.4.The modification of the typical sequence of aggressive behavior

The typical 4 phases aggressive sequence may be modified this way:

• The threat becomes less structured et includes more signs of impulsiveness or of fear ;

• The attack phase loses control et becomes more violent, resulting in bites unstopped by appeasing or submissive behavior of the agonist/target;

• The ending phase that should exist if the target is a member of the group or if the intruder is at large (further than the security distance), may be reduced by operant conditioning, may disappear if the target is unknown or edible, or may be replaced by flight (escape) 

•  The refractory phase may disappear by operant conditioning, impulsiveness and when the dog tries to ensure its survival; then the dog may use repeated attacks.

5.4.5.Overlapping

All the aggressive behavioral sequences are overlapping and seem, then, to be in continuity from mild to severe (lethal).

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6.The descriptive-contextual classification

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© Dr Joel Dehasse - Behaviorist veterinarian - 2004-01-25