Fearful Behavior—Genetics and the Environment

Fearful Dog (Fearful Behavior—Genetics and the Environment)

Two essential aspects of fear: (1) Fearful behavior has genetic and learned components, and (2) our pets may show fearful behavior because we have taught them that without being aware.

We usually distinguish between rational or appropriate and irrational or inappropriate fears. The latter are called phobias, i.e., fears that are disproportional to the dangers in question, although some phobias do have a survival value.

Fear mechanisms serve the survival of organisms by producing appropriate behavioral responses. Hence, evolution has preserved it, subject to adaptive changes throughout time and according to the posed environmental challenges. From an evolutionary perspective, the particular fear behaviors of a species may be an adaptation that was useful at some point in the past. The distinctive responses to fear stimuli may have emerged and developed during different periods. For example, fear of heights, common to most mammals, has probably developed during the Mesozoic period; and fear of snakes, usually in simians, during the Cenozoic period. Claustrophobia, agoraphobia, and aquaphobia may also have their origins in evolutionary adaptations.

Predators and prey have different strategies to deal with threats. Their behavioral strategies evolved throughout millennia under the constant struggle for survival. Predators avoid dangerous stimuli by creating distance, escape being the favored strategy. Prey animals freeze preferentially when the predator is still relatively far away, but when distance decreases to a critical value, the animal flees. Thus, flight appears to be a genuine unconditional response to the unconditional stimulus consisting of a predator at a critical distance.

Fearful responses and their intensity seem to be a consequence of predisposing traits, resulting from many gene-environment interactions during the development of the individual. The latest research has established a genetic basis for fearful behavior. Researchers conducted studies with humans as well as other animals. In humans, researchers have been able to study the effect of genetics (family lines and twins) and environment (adoption cases).


Fleeing is the first strategy when facing a threat. Horses seldom gallop in nature except when fleeing from a predator.

Flight is the primary strategy animals use in the face of a threat. This behavior is associated mainly with the sympathetic nervous system, which mobilizes the organism for the so-called fight-or-flight response originally described by Cannon. While flight is an active coping strategy when facing danger, freezing (immobilization) and hiding are passive coping strategies. Depending on species, such a strategy is the next-best option to flight. Animals freeze and hide when escape is impossible. Freezing implies an inhibitory activity in the autonomic system (hypotension, bradycardia), formerly described by Engel and Schmale as a conservation-withdrawal strategy.

Thanatosis, or tonic immobility, is an extreme form of freezing behavior. For example, white-tailed deer fawns (Odocoileus virginianus) can lower their heart rate to 38 beats per minute (from about 155) for up to two minutes.

Whether an animal has a preference for an active or a passive defense strategy is not solely a question of context. Research shows that some animals do prefer one strategy rather than the other. In exactly the same situation, two animals may respond differently. The interesting point is that these patterns, both behavioral and neuro-endocrinal, seem to be consistent. Some researchers suggest that this may explain why some individuals are more resistant to stress and stress-induced malfunctions than others. Researchers found the tendency to react one way rather than the other to run in families, suggesting a genetic component. The experiments were conducted with rats and mice, but we have no reason to suspect that studies of other species would not yield the same results.

Fear is probably experienced similarly in many species. All mammalian species show three different sites in the brain where electrical stimulation will produce a complete fear response: (1) the lateral and central regions of the amygdala, (2) the anterior and medial hypothalamus, and (3) areas of the PAG, the periaqueductal gray, which is the gray matter in the midbrain involved in the modulation of pain and defensive behavior. Researchers have also studied defensive strategies in various species and concluded that human reactions to threatening stimuli are not qualitatively different from nonhuman mammals.


The early development has a critical influence on how animals will respond to challenges, stress and fear eliciting stimuli.

The amygdala seems particularly relevant. We suspect that it may have a significant function in regulating many facets of social behavior. It also appears that threatening stimuli activate the amygdala, which in turn has a decisive influence on the cognitive mechanisms of the individual, including the perception of the environment, selective attention (relevant for learning), and memory.

Conclusion: Not surprisingly, and in line with many other behavioral traits, fearful behavior depends upon two different factors: (1) a genetic predisposition and (2) the influence of the environment. Environmental factors during the development of the young individual may be critical in its ability to cope with stress and fear-eliciting stimuli. Early experiences appear to affect the neural and biochemical systems involved in fearful behavior and in dealing with stress—as well as learning processes and the capacity to deal with threatening stimuli in adulthood. Maternal prenatal stress may also produce changes in the brain morphology of the fetus and, consequently, in its way of reacting to stress and fear-eliciting stimuli, later in life.

While some fear responses are innate, others are learned. Conditional fear provides a critical survival-related function in the face of a threat by activating a range of protective (or defensive) behaviors. Therefore, we can presume that all animals will be ready to identify and retain the memory of any stimulus or situation they have perceived as potentially dangerous or threatening. Thus, it is natural and easy for animals to develop fearful behavior.

Watson demonstrated how fear could be a conditioned response with his famous (or infamous) experiments on Little Albert in 1920, who learned to fear a white rat. Some of the fear behavior of our pets, particularly dogs and cats, are created by us. An event that in itself might pass nearly unnoticed may be blown up to a disproportionate relevance if associated with a strong reaction of the owner. Dogs (and children) often face situations with unexpected and somehow aversive results, which they would soon forget if it weren’t for the exaggerated reaction of the owners (parents). All living organisms are, in principle, prepared to deal with discomfort, aversive experiences, and failure. The problem is when these assume proportions out of context because they are additionally reinforced. For example, many dogs fear strangers because their owners fear that the dogs fear strangers, and their reactions reinforce the dogs’ disposition to be cautious about strangers. Often, and unaware of it, the owner reinforces the fearful response while attempting and believing that he/she is reassuring the dog. That is conditioned (learned) fear behavior.

We saw it clearly in the 1980s when we performed some experiments at Ethology Institute. A litter of puppies from a suspected line of dogs prone to show fearful behavior exhibited entirely distinct behaviors one year after we had placed them in six different homes. The dogs reflected, indeed in a significant degree, the attitude of their owners toward novelty and challenges. We repeated the experiment with another litter, this time from a confirmed non-fearful line, and the eight puppies showed the same tendency again when we tested them one year later. Even though there was a tendency for the dogs from the fearful line to be on average more cautious and the others to be bolder, they overlapped one another in the middle range of responses. Our tests did not include enough animals to enable us to draw a conclusive answer as to the question of genetics versus the environment in this aspect. However, they pointed out the importance of the environment, at least in what concerns the average domestic setting in which we can expect dogs to grow.


Cannon, W. B. (1915). Bodily Changes in Pain, Hunger, Fear and Rage. New York, NY: Appleton.

Engel, G. L. and Schmale, A. H. (1972). Conservation withdrawal: a primary regulatory process for organic homeostasis. In: Physiology, Emotions and Psychosomatic Illness. New York, NY: Elsevier; 1972:57–95.

Kavaliers, M. and Choleris, E. (2001). Antipredator responses and defensive behavior: ecological and ethological approaches for the neurosciences. Neurosci Biobehav Rev. 2001;25:577–586.

Koolhaas, J. M. et al. (1999). Coping styles in animals: current status in behavior and stress-physiology. Neurosci Biobehav Rev. 1999;23:925–935.

McFarland D. (1987). The Oxford Companion to Animal Behaviour. Oxford, UK: Oxford University Press.

Panksepp, J. (1998). The sources of fear and anxiety in the brain. In: Panksepp J, ed. Affective Neuroscience.New York, NY: Oxford University Press; 1998:206–222.

Parmigiani, S., Palanza, P., Rodgers J. and Ferrari, P. F. (1999). Selection, evolution of behavior and animal models in behavioral neuroscience. Neurosci Biobehav Rev. 1999;23:957–970.

Perrez, M. and Reichert, M. (1992). Stress, Coping, and Health. Seattle, Wash: Hogrefe & Huber Publishers.

Steimer, T. (2002). The biology of fear- and anxiety-related behaviors. Dialogues Clin Neurosci. Sep 2002; 4(3): 231–249.

Watson, J. B. (1970). Behaviorism. 7th ed. New York, NY: WW Norton & Company.

Weinstock, M. (2001). Alterations induced by gestational stress in brain morphology and behaviour of the offspring. Prog Neurobiol. 2001; 65:427–451.

Featured image: Dog showing fearful behavior. Paw lifting indicates a beginning of pacifying behavior (photo by Lifeonwhite).

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Aggressive Behavior—Inheritance and Environment


This dog shows self-confident (dominant) aggressive behavior. This is instrumental aggressive behavior (photo from dog-adoption-and-training-guide).


This dog shows insecurity and aggressive behavior. This may be reactive-impulsive aggressive behavior, but may also be learned behavior (photo by petexpertise.com).


This dog (to the right) shows learned aggressive behavior. It may be impulsive-reactive, but it does not need to be (photo by onegreenplanet.org).

Having dealt with the definition of aggressive behavior in an earlier article, we will now analyze the various types of aggressive behavior and their correlation to genetics. Although a strong definition of aggressive behavior is a promising step to understand it, we have not resolved all matters and still need to clarify a few other terms. Note that in the following, to make it shorter, we will use aggression and aggressive behavior interchangeably. 

When studying human aggression, it is common to subdivide it into two types: (1) instrumental aggression, which is purposeful or goal-oriented; and (2) reactive-impulsive aggression, which is elicited by loss of emotional control and often manifests itself as uncontrollable or inadequate actions.

Let us also note that, “Aggression differs from what is commonly called assertiveness, although the terms are often used interchangeably among lay people (as in phrases such as ‘an aggressive salesperson’” in Quadri and Vidhate’s words. They also state, “Predatory or defensive behavior between members of different species may not be considered aggression in the same sense.” I would go a step further and insist we do not consider these behaviors as aggressive behavior in any sense.

Aggression Types

A distinction in types of aggressive behaviors is between (1) pro-active (also controlled and instrumental) and (2) reactive-impulsive. The former is not an end in itself, only the means to achieve a goal. There are no strong emotions involved. On the contrary, its effects depend on deliberate and well-timed action. The latter has no goal in itself and is marked by intense emotions. In short, researchers of aggressive behavior in children have found it helpful to distinguish between reactive (impulsive) from proactive (instrumental) aggression.

Modern frustration-aggression theory claims that anger is a reaction to an aversive experience, including frustration. It emphasizes the importance of moral violation as justifying the expression of aggressive behavior.

The question is whether we also find these types of aggressive behavior in animals other than Homo sapiens sapiens. Being an evolutionary biologist and a good Darwinist, I am always highly suspicious of any statement claiming that a trait is exclusive to one single species. The odds of that happening are worse than winning the big lottery.


Do animals other than humans have morality, and will they fight for a cause? That is a difficult question because I cannot envisage any way of verifying it. In that sense, some would even call it a meaningless question. 

Let us analyze the evidence we have. We know that some animals show empathy and altruism, widely recognized as conditions for morality. Shermer points out that humans and other social animals share the following characteristics: “[
] attachment and bonding, cooperation and mutual aid, sympathy and empathy, direct and indirect reciprocity, altruism and reciprocal altruism, conflict resolution and peacemaking, deception and deception detection, community concern and caring about what others think about you, and awareness of and response to the social rules of the group.”

However, we can account for all these characteristics in terms of evolutionary costs and benefits and using models based on evolutionarily stable strategies. We need not introduce a new term, morality, to explain that. Therefore: if humans show moral behavior, so do other species, albeit differently. What we might need to concede is that sometimes quantitative differences amount to qualitative differences. Hence, showing these traits to such a high degree, as is the case in humans, justifies us coining a new term, morality.

Suppose that is the case (and I’m only theorizing). Then, it makes sense to label some human behavior as moral and disregard the possibility of morality in other animals (unless remarkable discoveries enlighten us differently).

Thus, if it does not make sense to analyze non-human animals’ behavior in terms of morality, then it follows that we can neglect reactive-impulsive aggression caused by violation of moral rules in those animals.

However, we cannot dismiss the same behavior caused by loss of emotional control because non-human animals can also lose control over their emotions. The tricky part here is, as always, the term emotion, which is vague and, therefore, one that biologists prefer to avoid.



Emotions and Reactive-Impulsive Aggressive Behavior

What is an emotion? According to Schacter, an emotion is “[
] a positive or negative experience that is associated with a particular pattern of physiological activity” caused by hormones, neurotransmitters, dopamine, noradrenaline, serotonin, and GABA. We find all these in some non-human animals; therefore, if we can accept the above definition of emotion, we must concede that if we can show emotional behavior, so can they.

The only way it makes sense when dog people speak of dogs being reactive (meaning they growl, snarl, attack, or bite someone) is that dogs display reactive-impulsive aggressive behavior. It is still, by all means, aggressive behavior, just one type that may or may not exist to some considerable degree in non-human animals, depending on whether I am right or wrong in my theorizing.

Recognizing and identifying reactive-impulsive aggression may be advantageous because research shows that it may be easier deterred than instrumental aggressive behavior. Reactive-impulsive aggression appears to result from a distorted perception of competition, the aggressive individual not realizing that there are evading routes, and enhanced by the inability to control the associated emotions. There is also evidence that reactive-impulsive aggression (contrary to instrumental aggression) is related to low serotonin levels in the brain. On the other hand, classifying all canine aggressive behavior as reactive-impulsive, as it seems to be the practice these days, may turn into a fatal mistake with extremely severe consequences.

A dog displaying aggressive behavior can show it self-confidently (what we, ethologists, call dominant behavior) or insecurely (showing submissive behavior—not fearful). The former is not reactive-impulsive—it is instrumental and goal-oriented. The latter might be if the dog does not realize that a clear display of submissive behavior or flight would solve the problem. This kind of aggressive behavior may be: (1) the consequence of inadequate imprinting and socialization (the dog did not learn how to solve social conflicts), (2) the result of inadvertently reinforced behavior. Dog owners reinforce their dog’s reactive-impulsive aggressive behavior attempting to do what they call ‘calming down the dog.’ The dog growls, they say, “quiet ” (or similar), the dog looks at them, and they reinforce that with a treat and a “good job.” It doesn’t take many repetitions for the dog to learn that displaying aggressive behavior provides attention and food.

The term reactive does not belong to ethology, which classifies behavior by function. I don’t know how it came into dog training, but I suspect a psychologist introduced it, and dog people liked it because it sounded better to say, “My dog is reactive” than “My dog shows aggressive behavior.” Ironically, the term places the full responsibility for unwanted behavior on the owners—reactive-impulsive aggression is either the result of poor imprinting/socialization or inadequate training.


Is Aggressiveness Inherited?

Heritability studies attempt to determine whether a trait passes from parent to offspring. Some genetic lines in many birds, dogs, fish, and mice seem to be more prone to aggression than others. Through selective breeding, we can create animals with a tendency to show more aggressive behavior.

Some aggressive behavior is evolutionarily advantageous, and some are not and might be an impediment to social cohesion. Maynard Smith states that it is not surprising for aggressiveness to have a strong genetic correlation, given the high likelihood of both potentially positive and negative selective discrimination throughout evolution.

Research has uncovered many factors that contribute to aggressive behavior. Disruption of the serotonin system is a highly significant feature in predisposing aggression. There is a correlation between testosterone levels and aggression. Extremely low levels of blood sugar (hypoglycemia) may elicit physiological changes and aggressive behavior.

Most researchers agree that we must consider the influence of genes, not in isolation, but as functioning in the whole genotype, as well as the effect of the environment. Thus, future research in the genetics of aggressive behavior may very well focus on epigenetic factors.

Doubtless, most behavior traits, except simple reflexes, contain a genetic plus an environmental component. No behavior will develop without the appropriate genetic blueprint, and no behavior (again except for a few simple patterns) will show in the absence of the correct environmental stimuli.

It is probable each organism filters and selects stimuli from a wide range in its habitat according to its genetics, thereby creating its uniqueness of experiences. As Bock and colleagues say, we make our own environment. I have no reason to suspect that the same does not happen with other animals.





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Featured image: These two dogs are both equally self-confident (showing equal dominant behavior). Any aggressive behavior deriving from this situation will not be reactive-impulsive, but instrumental (photo from dog time.com).

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