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Behaviour, Development and Evolution

Patrick Bateson

5. Early Experience and Later Behaviour1

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  • 1 This chapter is drawn in part, with permission of Springer, from Bateson, P. (1983), The interpreta (...)
  • 2 Clarke, A.M. & Clarke, A.D.B. (1976), Early Experience: Myth and Evidence. London: Open Books.

1The conviction that experience can exert a greater influence at some times of life than at others is deeply rooted in conventional thinking about humans and other animals. The disturbing picture of a child missing the developmental bus by not being treated in a particular way at specific times has been strongly challenged.2 In many instances, it is possible to resolve the apparent contradiction between the view that the young are especially susceptible to particular experiences at particular times and the view that adults can also be affected by experience. This is because the effect of early experience involving influence or instruction from the environment can arise not so much through an incapacity to learn as through a reluctance to do so outside the period of sensitivity. When such reluctance can be overcome, it is possible for the older individual to learn about new things once again. It is important therefore to deal with the evidence for the effects of early experience separately from the mechanisms that control the timing of sensitive periods in development.

2Many people who study the development of behaviour in humans feel uncomfortable, or even hostile, when evidence from animals is mentioned. It is as though the evidence is tainted with rigid determinism and with the worst excesses of biologists intent on taking over the social sciences. It is a great pity that such attitudes are so prevalent because the phenomena encompassed by the evidence can provide highly promising gateways to an understanding of developing mental processes. A ‘sensitive period’, or one of its synonyms, ought merely to refer descriptively to the evidence that an individual’s characteristics may be most strongly influenced by a given event at a certain stage of development. It is not an explanatory concept. It should not suggest that other events exert their maximum influence at the same stage. Nor should it carry implications about what might have given rise to the particular sensitive period that has been described.

3In terms of an analogy with a moving train, the window of a particular compartment in the developmental train opens at a particular stage in the journey and then stays open. As a result of what an occupant learns about the outside world, it subsequently averts its gaze from anything strange. Because it can learn nothing until the window does open, the timing of the ending of the sensitive period is also dependent on the internal processes responsible for opening the window in the first place. If this analogy can be pressed a little further, it looks as though the occupant can, under certain circumstances, be persuaded to study strange things outside the train later in the journey, and when it does so it is influenced by what it sees.

4It is possible to reconcile the view that early experience is important with the view that nothing is irreversible. The general point is that it may be possible for the distinctive features of behaviour to be formed in a particular stage in development and yet for the processes generating those features to be reactivated at much later stages in the life-cycle. An understanding of the mechanisms can explain why, under certain circumstances, the evidence for sensitive periods seems to evaporate.

  • 3 Freud, S. (1905), Drei Abhandlungen zur Sexualtheorie. Leipzig: Franz Deuticke.

5Sigmund Freud’s psychoanalytical theory, which was unusual at the time, reflected his belief that seemingly irreversible influences from childhood could be overcome in adults.3 This view was central to Freud’s method of therapy for those whose lives had been adversely affected by their early experience. Nowadays the idea is widely accepted and is implicit in the vast self-help industry, which is built on the supposition that people can change themselves. Indeed, the pendulum has swung so far that it often seems as though people should be able to change their behaviour and personality as readily as they change their clothes.

6The older, and perhaps excessive, emphasis on early experience may have been rejected because of its implied pessimism that once someone had missed the developmental train, nothing could be done to help them thereafter. The grounds for optimism are in fact considerable, and evidence for sensitive periods early in development may be readily reconciled with evidence for subsequent changes in behaviour. This is most clearly seen when the experience that could cause the change is not normally encountered in later life. An unwillingness to eat novel food means that people will not encounter the flavours and textures that might change their preferences. But it is not just a matter of preference. The mechanisms in the brain that protect behaviour from change can be stripped away so that plasticity is once again possible.

Sigmund Freud. Photo by Max Halberstadt (1922), Wikimedia,​wiki/​File:Sigmund_Freud_LIFE.jpg, Public Domain.

7The behaviour patterns that are typical of gender, such as the style of play in boys and girls, may be amplified or minimised as the result of social influences from peers, teachers and parents. In the same way that a boy can become less ‘boyish’ in social circumstances that reduce gender differences, some shy children become less shy as they develop. Equally, some outgoing children become more withdrawn. The evidence that birth order has a significant effect on personality points once again to the subtle role of experience in development. Other factors, such as sudden changes in a family’s economic circumstances, can also have big effects on what happens to a child.

Washing the brain

8Academics are sometimes caricatured (not entirely unfairly) as accumulating more and more detailed knowledge about a subject on which their focus becomes ever narrower. In the image of Waddington’s epigenetic landscape (see Chapter 3), they have descended into an intellectual valley from which escape becomes increasingly difficult. They are stuck in their own silos of knowledge. Even so, some scholars manifestly do break out of these narrow confines. Indeed, a much admired feature of the wisest academics is their ability to make connections between different bodies of knowledge. Is such willingness to branch out equally true for their more deeply seated beliefs and attitudes, such as their political persuasion or their sociability? Most people would say ‘no’. Values are established in early life and, it is supposed, remain firmly fixed thereafter.

9American public opinion which had been comfortable in this belief took a jolt in the Korean War. About a third of the 7,000 American prisoners of war collaborated with their Chinese and North Korean captors, and 21 refused to return to the USA when the war was over. These ‘conversions’ generated consternation in the USA and stimulated an intense examination of the techniques used by the captors of the prisoners of war. Many of the apparent conversions turned out to have been little more than the effects of prolonged deprivation of sleep or, in some cases, self-preserving attempts to secure better living conditions. The so-called brainwashing methods were neither subtle nor sophisticated. Even so, some of the prisoners who had been subjected to terror, physical hardship and intensive indoctrination did seem to have changed their values and political allegiances in a more fundamental way.

10The origins of brainwashing lie much further back than the Korean War. Echoes can be found, for instance, in the Christian revivalist conversions in eighteenth-century America. During a religious crusade in Massachusetts in the 1730s, the theologian Jonathan Edwards discovered that he could make his ‘sinners’ break down and submit completely to his will. He achieved this by threatening them with hell and thereby inducing acute fear, apprehension and guilt. Edwards, like many other preachers before and after him, whipped up the emotions of his congregation to a fever-pitch of anger, fear, excitement and nervous tension, before exposing them to the new ideas and beliefs he wanted them to absorb. To this day, live rattlesnakes are passed around some congregations in the southern parts of the USA; the fear they induce can impair judgement and make the candidates for conversion more suggestible. Once this state of mental plasticity has been created, the preacher starts to replace their existing patterns of thought. And constant fear is, of course, a hallmark of totalitarian regimes where dissenting individuals live under the unremitting threat of detention, torture or execution.

  • 4 Sargant, W. (1957), Battle for the Mind: A Physiology of Conversion and Brainwashing. London: Heine (...)

11The British psychiatrist William Sargant, working in the middle of the twentieth century, was deeply interested in the mind-moulding techniques, and noticed the importance of high emotion in the process of religious conversion.4 He drew on a wide range of human experience, including that of military brainwashing. He extended his inquiry to the beneficial uses of stress in psychotherapy. In the Second World War Sargant tried to help soldiers suffering from battle fatigue. As part of the therapy, he and his colleagues would deliberately arouse strong emotions in their patients, about events that had no direct connection with the trauma they had experienced.

  • 5 References to flooding in psychiatry are given in (...)

12Sargant argued for the importance of the emotional reaction in therapy, whereby patients are made anxious, guilty and even angry by their therapist and, in consequence, become able to change their previous patterns of behaviour. Sargant’s method has something in common with the psychological therapeutic technique of ‘flooding’, in which someone suffering from a phobia is deliberately frightened in the presence of the object or situation towards which they are phobic — for instance, by placing a large spider onto the chest of the patient who is terrified of spiders.5 Contrary to what intuition might suggest, the patient’s phobia may sometimes be reduced.

13It is common practice around the world for army recruits to be treated brutally in the early stages of their training. The individual is broken down through physical and mental pressure before being rebuilt in the form required by the military. The recruits are verbally abused, made to perform pointless menial tasks, and forced onto long marches carrying heavy equipment. By degrees their platoon becomes their family. Away from armies, other methods for inducing psychological plasticity include social isolation, fasting, lowering blood glucose with insulin, physical discomfort, chronic fatigue and the use of disturbing lighting and sound effects.

14The so-called Stockholm syndrome, also known as ‘terror bonding’ or ‘trauma bonding’, may be yet another instance of psychological plasticity induced by emotional trauma. The term takes its name from an incident in Stockholm in the 1970s, in which a woman who was taken hostage in a Stockholm bank following an unsuccessful robbery formed a strong and long-lasting emotional bond with her captor. She even remained faithful to him during his subsequent imprisonment. Her strange reaction was not unique. Many other victims of violent hostage-taking have ended up siding with their captors against the authorities who were trying to rescue them. Being taken hostage is obviously a traumatic experience, and the hostage-takers may be equally frightened because their lives are on the line as well. In such circumstances, where hostage and captor are exposed to each other while both are emotionally highly aroused, a strong emotional bond may form, bizarrely uniting them against the world outside. As with the various military, political, religious and therapeutic techniques for changing the way adults think and behave, the crucial element is the combination of psychological stress and suggestion.

15Comparable cases in which trauma has induced behavioural plasticity have been observed in other species as well. Adult wild horses are commonly ‘broken’ by traumatising them whilst exposing them to humans. A traditional but brutal method involves near-strangulation with a rope; even the wildest of wild horses can be reduced to gentle submissiveness in as little as 15 minutes using this technique. Unsocialised adult dogs can similarly be induced to form strong attachments to humans by means of traumatic discipline. (The fact that these practices work does not make them desirable.) An anecdotal but nonetheless illuminating case concerned a remarkable change in an adult female Soay sheep, which was part of a small flock living in the grounds of the University Sub-Department of Animal Behaviour at Madingley, near Cambridge. The Soay sheep were wild, avoiding human beings, and the female in question was no exception. Then, one spring, she had a particularly difficult time giving birth. It was eventually necessary for Sub-Department’s staff to assist, by catching the mother and pulling her lamb out. This was undoubtedly a traumatic experience for her. Ever afterwards, until she died, this sheep remained strongly attached to humans and would follow people around as they moved about the grounds of the laboratory. The trauma of the birth, combined with simultaneous exposure to people, brought about a profound and long-lasting change in this animal’s behaviour.


16The concept of extreme fear or emotional arousal inducing plasticity helps make sense of many diverse examples of behavioural change. What might be the neurobiological mechanisms underlying this effect? How does trauma make someone susceptible to fundamental changes in their thoughts and values? What might be the biological link between psychological stress and the processes of plasticity and change in the nervous system?

17High levels of psychological stress are associated, amongst other things, with the rapid synthesis and turnover of the neurotransmitter substance noradrenaline. This chemical messenger of the nervous system has been implicated as an enabling factor in making the adult brain become plastic again. Noradrenaline (known in the USA as norepinephrine) is released in the mammalian brain, at the endings of neurons throughout the body, and from the adrenal glands just above the kidneys. It is released, amongst other things, in response to psychological stress; in humans, a mildly stressful situation such as giving a public speech will typically elicit a 50% rise in the amount of noradrenaline circulating in the bloodstream.

  • 6 Pettigrew, J.D. & Kasamutsu, T. (1978), Local perfusion of nor adrenaline maintains visual cortical (...)
  • 7 Baroncelli, L. et al. (2016), Experience affects critical period plasticity in the visual cortex th (...)

18An experiment on the visual system of cats gave some valuable insights into the connection between noradrenaline and plasticity.6 The mammalian visual system is normally changeable only during an early stage in the individual’s life. The capacity of an eye to stimulate neurons in the visual cortex of the cat’s brain depends on whether that eye received visual input between about one month and three months after birth. If one eye is deprived of visual stimuli during this period it virtually loses its capacity to excite cortical neurons thereafter, no matter how much visual stimulation it receives. The eye consequently becomes functionally blind, even though it remains physically unimpaired. Once the dominance of the other eye is established, it is exceedingly difficult to change the relationship with the unused eye. Similarly, binocular vision cannot easily be disrupted in normally reared individuals once it has become established. Infusing noradrenaline into one hemisphere of the visual cortex of older cats can re-establish plasticity and enable further change to occur in response to visual experience. If normally-reared animals are deprived of the use of one eye during the period of noradrenaline infusion, binocular control of the neurons is lost in the visual cortex of the hemisphere that was infused. No such change occurs in the visual cortex of the other hemisphere. In other words noradrenaline can reverse in adulthood what would otherwise be unchangeable.7

If one eye is occluded in early life by, say, infection, the other eye becomes dominant for the rest of the cat’s life. Photo by Patrick Bateson, CC BY 4.0.

Continuity and change

19The variety and complexity of behaviour and its underlying psychological systems inevitably means that any sweeping statement about the possibility of change must eventually come unstuck. The self-help industries that promise relief from shyness, depression, sloth, obesity, or addiction to nicotine deliver results only some of the time. Once developed, some patterns of behaviour are strongly buffered against subsequent change. Preference for certain types of food and for particular places tend not to change. They may be stable for good reasons, since change can be disruptive and costly. On the other hand, not to change may, in certain circumstances, carry an even bigger cost, which perhaps explains why behavioural characteristics tend to become plastic under conditions of stress.

20When one aspect of behaviour changes it does not imply that everything else must change as well. But whatever the complexities of development and the inadequacies of current understanding, it is clear that adults really are capable of changing — more so, perhaps, than many suppose.

  • 8 This conclusion is supported by the work on Cognitive Behavioural Therapy which is used to treat a (...)

21The psychiatric evidence for rehabilitation leaves untouched the question of which forms of behaviour, once developed, are most strongly buffered against subsequent change. It seems likely that in adults cognitive processes are more easily changed than those underlying their emotions.8 Adaptations that protect certain well-developed preferences and habits from alteration are to be expected. Fear of novelty, though general in its effects, would serve precisely this function.


22A positive point that emerges is that evidence for sensitive periods in development can be readily reconciled with evidence for subsequent changes in behaviour. This is most clearly the case when the form of treatment involves experiences that would not normally be encountered in later life. Once the mechanisms protecting behaviour from change are stripped away by suitable treatment, change resulting from renewed plasticity is once again possible. Any changes in sensitivity that are found imply no particular mechanism. The search for what might generate a sensitive period in development is a separate enterprise. Even so, the stability of some aspects of behaviour, once formed, can be changed under certain conditions such as chronic stress. The flexibility make good sense in biological terms since it enables the individual to cope in a changed environment. The capacity has the appearance of good design.


1 This chapter is drawn in part, with permission of Springer, from Bateson, P. (1983), The interpretation of sensitive periods. In: A. Oliverio & M. Zappella (eds.), The Behavior of Human Infants. New York: Plenum Press, pp. 57–70, Much of this chapter is devoted to change and resistance to change in humans.

2 Clarke, A.M. & Clarke, A.D.B. (1976), Early Experience: Myth and Evidence. London: Open Books.

3 Freud, S. (1905), Drei Abhandlungen zur Sexualtheorie. Leipzig: Franz Deuticke.

4 Sargant, W. (1957), Battle for the Mind: A Physiology of Conversion and Brainwashing. London: Heinemann.

5 References to flooding in psychiatry are given in

6 Pettigrew, J.D. & Kasamutsu, T. (1978), Local perfusion of nor adrenaline maintains visual cortical plasticity. Nature 271: 761–763,

7 Baroncelli, L. et al. (2016), Experience affects critical period plasticity in the visual cortex through an epigenetic regulation of histone post-translational modifications. J. Neurosci.

8 This conclusion is supported by the work on Cognitive Behavioural Therapy which is used to treat a number of psychiatric disorders (e.g. McKay D. et al. (2015), Efficacy of cognitive-behavioral therapy for obsessive-compulsive disorder. Psychiatry Research 225.3, 236–246,

Table des illustrations

Légende Sigmund Freud. Photo by Max Halberstadt (1922), Wikimedia,​wiki/​File:Sigmund_Freud_LIFE.jpg, Public Domain.
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Légende If one eye is occluded in early life by, say, infection, the other eye becomes dominant for the rest of the cat’s life. Photo by Patrick Bateson, CC BY 4.0.
Fichier image/jpeg, 17k


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