Domestic Mammals

Wolf Herre & Manfred Rohrs

(The following is an excerpt from the long essay "Animals in Captivity" published in the outstanding 5 volume Grzimek's Encyclopedia of Mammals. It is an illuminating description of the mental and behavioral deterioration caused by domestication. The below chart shows decrease in brain size for domesticated species).


Wild Form

Decrease in
Brain Weight

Wild Form

Decrease in
Cortex Volume











Guinea Pig








































There is a close correlation between brain changes and behavioral changes in domestic animals. It has been primarily gregarious wild species that have been domesticated.  In captivity, social behavior patterns changed.  Many social structures that have the effect of preserving the species in the wild lose their purpose in captivity.  Indeed, in view of high-density living conditions, social structures are disadvantageous for contact of domestic animals among themselves and with humans. This can be demonstrated in wolves and domestic dogs. Wolves form packs and the behavior patterns of individual members vary widely. There are powerful, successful fighters whose alertness and powers of observation are quite poor.  In other members, these capabilities are well-developed, but "fighting spirit," power, and agility are lacking.  The cooperation of the differently skilled animals is important for successful predation by the pack.  In domestic dogs, animals with minimal aggressiveness and alertness predominate.

In the wolf pack, a hierarchy is in effect and is repeatedly contested. Wolves assume their positions in a hierarchy only for a certain period.  In a group of poodles, the hierarchy is remarkably stable for a very long period.  Once a hierarchy is established, poodles and other domestic dogs submit to it over the long term. This makes them that much more suitable for domestic life and for human contact.

Wolves (that is, the wild species) are characterized by powerful, well-coordinated movements. Their actions appear to be very finely tuned, and they are much more mobile than domestic dogs.  Poodles, on the other hand, have lost the fluid movements of the wolves in their forms of locomotion, particularly when trotting and galloping. They also do not show the very tense orientation posture of the wolves.  In addition, they lack the "observation jump," for which considerable physical control is required. Furthermore, certain positions of individual body parts that serve the purpose of social communication in wolves have been lost or reduced in dogs. Poodles show less than half the expressive social behavior of wolves, and what they have retained is performed in weaker form.

The same is true of play behavior. The very expressive running games of wolves are present in poodles only to a small extent. In the play of wolves, components of the hunting drive mature separately and are not coordinated until later. The triggering mechanisms of some of these behavior patterns mature very early. Such behavior patterns are observed to begin just as early in poodles, but many of them which occur first in isolation do not become further differentiated later. Adult poodles behave essentially like young wolves. The power and strength of attacks are much greater in wolves than in poodles.  While a poodle attacks strange dogs only in its own territory, the dislike for strangers to the pack is much stronger in wolves, particularly during the rut.  An increase in aggressive behavior has not been observed in poodles during specific seasons or when females are in heat. In this respect as well, their behavior resembles that of young wolves who have not yet reached sexual maturity.

Striking differences are also found in feeding habits.  Wolves are decidedly social at the feeding site; juveniles and nursing mothers with high food requirements have priority.  Males take part in raising the young by feeding them.  This is not the case with male poodles.  They are quite aggressive at the feeding place. If there are juveniles in a group, wolves show a protective guarding behavior, while poodles in such a situation show no change in behavior patterns.

Differences are also found between the wild ancestor and the domestic form in intraspecific communication.  Both genetic factors and learning processes play a role here. Wolves, as well as other ancestor species, have a highly differentiated communication repertoire consisting of a variety of gestures and sounds.  Different combinations of the individual elements have different meanings. In close interaction, expressive gestures and soft, high notes are significant; in communicating over distances, body postures, a variety of howls, and sometimes barking are used.  In communication among domestic dogs, the gestures are less variable and less differentiated. Barking dominates the vocalization repertoire, even at close range.  Barking is usually just an expression of emotion.  Barking can be exaggerated, particularly in contact with humans, but it arouses one's attention.  Domestic dogs only rarely howl.  It is clear that wolves and domestic dogs are capable of the same vocalizations, but these capabilities are used differently.  Nervous control mechanisms and not differences in vocal organs are responsible for the preferred vocalizations.  Animals resulting from interbreeding of poodles and wolves produced peculiar mixed sounds and also showed different reactions to sounds and gestures.

Observation of differences between wild species and domestic forms is of interest in considerations of intraspecific communication systems in mammals, including humans.  It shows that, for the extent and meaning of communication within species of higher vertebrates, the production of sounds must be in harmony with the processing of messages transmitted and received by the central nervous system.  This is also true of gestures.  Hereditary factors that control the individual elements are independent of one another.  Species-specific units have been developed in the course of evolution.  Mammals are capable of memory and planned actions, and it is entirely justified to describe the intraspecific communication systems of mammals as species-specific "languages."  In captivity, intraspecific communication is reduced.  The individuals of a species of domestic animal no longer have much information to communicate. The relationship to humans has become the highest priority.  Behavior patterns, too, show how rapidly adaptation and selection can bring about far-reaching changes in populations. This state of affairs can be demonstrated with many other domestication-related behavioral characteristics.

Pigs are a further example of behavioral changes. Remarkable differences in behavior also exist between domestic pigs and wild boar.  In domestic pigs, the typical group structure of the wild ancestors is dissolved, the mobility drive is reduced, the flight behavior is less pronounced, and the flight distance is much smaller.  Wild boars are very aggressive and attack opponents even in groups; subduing this aggressive drive was an important prerequisite for domestication. Similarly, many elements in the search for food are no longer present in domestic pigs; predation, in particular, is very rarely observed. Wild boars hunt insect larvae, frogs, reptiles, rodents, hares, and even fawns. Fights among rival boars are not as fierce as in the wild.  Female domestic pigs lack the varied behavior patterns of nest building shown by female wild boars.

We will now attempt to bring the behavioral changes in domestic animals into some sort of order.  First, we shall describe some behavior patterns that have been reduced or completely lost in domestic animals.  Even in laboratory rats, one finds a strong decrease in overall activity, warning behavior, flight, and defensive actions, as compared to Norway rats. While Norway rats utter a characteristic cry when danger is near, this cry has been lost in laboratory rats. In the wild, male guanacos warn their family groups of danger with a high-pitched whinny, whereupon the group takes flight and the male follows, often attempting to divert the enemy.  Such behavior has never been observed in the llamas or alpacas which are kept under very free conditions in South America.  In general, it can probably be said that flight distances are considerably reduced in domestic animals and that flight activity has decreased greatly. In some domestic animals, flight behavior has been almost completely eliminated through artificial selection.

Aggressiveness can also be greatly subdued in many domestic animals.  Caged Norway rats kill mice put into their cages with high regularity; in laboratory rats, this is the exception.  If one puts two wild rats in a cage and administers electroshock, the animals fight unusually fiercely.  Laboratory rats under the same conditions, on the other hand, attempt to flee.  Humans have obviously valued subdued aggression from the beginning, since large, aggressive domestic animals are difficult to handle.

Behavior patterns dealing with acquisition of food can also be subdued or disappear in domestic animals.  The ferret, dog, and cat are domestic predators that normally display hunting behavior less frequently than their wild forms.  This may be related to the simple fact that these animals are fed by people.  Some domestic dogs and cats never catch, kill, or eat prey, even when it is offered to them.  In other cases, some of the hunting actions are absent.  For example, there are domestic cats that still catch and kill prey but do not eat it; others no longer catch and kill prey, but will eat dead prey.  In some domestic dogs, the last vestiges of predation behavior are gone; the chain of action stops at the pointing or setting stage.

The ability to catch prey need not always be lost in domestic pigs, by the way.  There are exceptions that show us that certain behavior patterns can develop separately from one another. For example, hunting pigs were raised from the eleventh to the fifteenth century in Hampshire, England.  One of these animals named achieved great fame. This hunting pig was far superior to many hunting dogs: it could track, set, and retrieve all game.

In domestic animals that subsist exclusively on grass and other plants, the search for feeding and grazing sites and the defense of these sites is absent in captivity.  However, recent research shows that, in these animals as well, behavioral changes in food selection are remarkable.  While many wild forms require certain food plants and can carefully select them from a rich food supply, domestic animals no longer have these food selection skills, even when they are given the freedom to choose.

On the other hand, exaggeration of behavior patterns may also occur in domestic animals. For example, the feeding drive is frequently considerably intensified.  Individual aspects of the hunting behavior of predatory animals may increase significantly.  Some domestic cats, for example, catch the same mouse repeatedly without killing it.  Others regularly carry killed prey into their nest or house.  Dogs can also be pronounced "rat biters." In some domestic dogs, the aggressive drive is not reduced, but is in fact elevated; they attack animals that a wolf would never attack.

There are exaggerations above all in the reproductive behavior of domestic animals.  Domestic animals generally reach sexual maturity earlier than wild animals; the number of litters and number of offspring are increased.  Sexual activity is greatly increased.  Exaggerations of behavior patterns may even lead to changed postures in domestic animals. In intimidation displays, the wolf moves its tail from its usual hanging position to a slightly curled, erect position over its back.  In some dogs, this intimidation posture of the tail has become a permanent feature.  A very inhibited wolf carries its tail between its legs, which can also be a permanent posture in domestic dogs.  These permanent postures can in no way be interpreted as an expression of permanent intimidation or permanent inhibition, however.

According to Konrad Lorenz, behavior patterns that originally coexisted in the wild can become separated in captivity.  When domestic dogs interrupt the hunting behavior after pointing, this is a disintegration of behavior patterns that belong together. The process of pair formation and monogamy described in wolves is not observed in domestic dogs.  Another group of behavioral changes in domestic animals, according to Lorenz, are changes in the area of triggering mechanisms, in which key stimuli release innate behavior patterns.  In domestic animals, the threshold for the innate triggering mechanisms may be raised or lowered, and certain actions can be triggered by substitute stimuli.  In other words, many domestic animals perform actions on completely wrong objects.  Substitute objects, such as balls of wool, stones, and sticks, are used by juvenile cats and dogs in play, but also by adults carrying out hunting behavior.  Sexual actions are also triggered by in domestic animals by very approximate key stimuli.  It is therefore possible to trigger domestic boars and bulls to engage in mating behavior using very simple dummies--a procedure used in artificial insemination.