XVI.2 During evolution, some taxons have developed mechanisms for behavior control that enable the individual to react to an environmental influence that the species has never experienced before

Behavior-controlling mechanisms have appeared during evolution to enable organisms to react adaptively to the widening spectrum of stimuli coming from their surroundings. An inborn fixed pattern of behavior is the simplest mechanism. Some inborn fixed patters of behavior activate autonomously during the individual’s ontogeny and life cycle, independent of the environment. They are activated without any external stimulus and their form and starting point are programmed genetically. In many cases, the neural system is not required for their coordination. This kind of behavior often occurs in plants, where it is accompanied or mediated by growth; it most probably also controls the embryogenesis of most organisms.

Inborn reflexive behavioris a type of behavior that is one step more complex. The unconditioned reflex is a prototype of this kind of behavior, but it is necessary to bear in mind that a simple reflex can be followed by a long sequence of other elements of behavior, of  which some are fixed and some learned (see below). The organism’s reaction to a specific external starting stimulus consists in the activation of another specific pattern of behavior (e.g. the familiar patellar reflex). The specificity of the external starting stimulus ensures that the given patterns of behavior will be initiated in situations that are advantageous for the organism. This type of control lacks plasticity; it develops entirely in the process of natural selection which does not enable the organism to react to the momentary situation. From a statistical point of view and in the long-time perspective, the existence of a fixed pattern of behavior can be advantageous, but in some situations, especially under changing conditions, such a behavioral pattern can be fatal. Moths would certainly tell us something very ugly, if they could, about their current experience:  For millions of years, they have oriented themselves according to light sources when flying in the dark; i.e. according to the position of moon and stars, objects infinitely far away from the practical point of view. If they were to do this in the present-day populated landscape, they would most likely end their lives by spiraling into hot light bulbs.

 A further step in the evolution of mechanisms controlling the behavior organisms is the learned pattern of behavior, of which the conditioned reflex is a simple form. The neural systems of many kinds of animals are adapted so that, when a trigger stimulus for a specific unconditioned reflex is repeatedly accompanied or preceded by another stimulus, the organism will, after some time, also react by launching the particular behavior pattern in consequence of this other stimulus.  The famous salivating Pavlov’s dogs are a textbook example of an experimentally produced conditioned reflex.

 Formation of conditioned reflexes and other types of learning provide animals with good behavioral plasticity. They enable each individual of the given species to adapt to the particular local conditions, which can differ from the long-term conditions under which the majority of this kind lives. The individual can even adjust its behavior to stimuli it never experienced before. If an adaptation to a unique lifetime situation is to be created (e.g. the need to recognize its parents), learning may occur in the form of imprinting. If the individual encounters the appropriate stimulus at a given moment, e.g. when a freshly hatched young goose meets a colored ball or Professor Konrad Lorenz, it will imprint the particular object into its memory as its mother and for the rest of its life this stimulus will remain a trigger for particular behavioral patterns. Behavioral patterns created by imprinting are long-term or permanent and do not need strengthening to last. On the other hand, once they are created they are usually irreversible; they can not be changed when the external conditions change. In contrast, standard learned patterns can disappear more or less rapidly. To last, they need to be strengthened continuously by a repeatedly occurring combination of the stimuli that produced the patterns. In a changeable environment, this is advantageous because reflexes that are no longer useful for the organism can give way to new ones. Conversely, imprinting is useful for stimuli that will probably not change during the individual’s life, e.g. recognizing its mother or members of its own species.


Another step in the evolution of behavior-controlling mechanisms is creating useful behavioral patterns through operant conditioning based oninner motivation. The organism’s motivation should be seen as a particular physiological state of the organism, not as an abstract term describing heading towards a goal. The basis for a new behavioral pattern is not the development of one of the many existing specific behavioral patterns, whose trigger stimulus would be connected with other outer time or locally associated stimuli. It consists in strengthening of those behavioral patterns that the organism has found to be connectedto a specific pleasant inner stimulus (Lorenz et al. 1974). Specifically, this entails behavioral patterns that evoke a feeling of pleasure or inhibit an unpleasant feeling of distress. Different stimuli coming through the organism’s senses are continuously transformed into a common pleasure-distress “currency”; this simplifies and makes more effective the creation and strengthening of momentarily useful behavioral patterns necessary for the survival of the organism. Transformation of the outer stimuli into the inner common currency enables the organism to free itself from the constraints of its material world. If – from the point of view of the fitness of the individual – it  is advantageous to seek a particular objectively unpleasant stimulus, e.g. one that is usually followed by an injury, biological evolution can “program” the members of the species to a certain form of  “masochism”; the objectively unpleasant stimulus will be perceived as pleasant in the particular situation (see examples of passive cannibalism in some kinds of arthropod males during mating) (Fedorka & Mousseau 2002).

Behavioral regulation through the above-described pleasure-distress mechanism can be compared to regulation by a proportional regulator, as the intensity of the output signal (e.g. the feeling of delight) is proportional to the intensity of the input signal – stimulus coming from the surroundings. In behavior control, a similar effect can be achieved through regulation by a derivation regulator (the intensity of the output signal is proportional to the fall or rise of the intensity of the input signal) and integration regulator (the intensity of output signal is proportional to the duration (and usually the intensity too) of the input signal) (Fig.  XVI.2). Integration regulators can be used to control the


Fig. XVI.2 Types of regulators. From the perspective of cybernetics, there are three basic types of regulators. In a proportional regulator, the intensity of the outgoing signal is directly proportional to the intensity of the incoming signal, in a derivative regulator the intensity of the outgoing signal is directly proportionate to the speed of the change in the incoming signal and, in an integrating regulator, the intensity of the outgoing signal is directly proportionate to the product of the intensity and the duration of the incoming signal. Units expressing the intensities of the incoming and outgoing signals and time have been selected arbitrarily for the chart.

spontaneous activity of organisms. If there is a prolonged lack of incoming stimuli, a phenomenon we can call “charging the boredom condenser” may occur. If the unpleasant feeling of boredom is too strong, the animal will try to discharge the “boredom condenser”, for example by playing. Play is – amongst other things – a highly effective way of testing new behavioral patterns. The patterns that have been shown to be effective for an individual with a particular phenotype in its usual environment can later be included into a behavioral repertoire of the individual.

The mechanism of motivation based on the pleasure-distress balance, i.e. a mechanism of “inner motivation” enables even signals very indirectly connected with satisfying a particular need to become a trigger for complex behavioral patterns. This – in consequence – makes it possible for the individual to react, not only to certain objects in the real world, but also to symbols that stand for the objects. It makes no difference whether these symbols are pheromones (i.e. chemicals primarily meant for communication between members of the same species), piles of droppings (rats’ markings for poisoned bait) or “Beware of the dog” warning signs on yard gates. The ability to mentally recognize symbols can finally lead to the emergenceofconsciousness, including self-consciousness. Consciousness and self-consciousness enable imagining situations and connections that have not appeared yet. Mostly, we can quite well imagine what would happen if we put our hand into a mad dog’s mouth without having to practically test the advantages or disadvantages of this kind of behavior.

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more
Draft translation from: Evoluční biologie, 2. vydání (Evolutionary biology, 2nd edition), J. Flegr, Academia Prague 2009. The translation was not done by biologist, therefore any suggestion concerning proper scientific terminology and language usage are highly welcomed. You can send your comments to flegratcesnet [dot] cz. Thank you.