The Human Beast

Why we do what we do

Trauma Resets Personality

Traumatic events as "deep" as personality.

Psychologists know that some aspects of personality are virtually unchangeable. These traits are described as “deep,” meaning that they are (a) biologically based and (b) difficult to change (1). You cannot turn a sociopath into a saint or crush the ego of a narcissist.

Such change is theoretically possible but it would require profound changes in brain biology. For instance, researchers shifted polygynous mountain voles to monogamy by altering brain receptors for the hormone oxytocin (2).

Deep means hard to change – not hard to acquire

A trait does not have to be genetically inherited, or even present at birth, to be deep. If you ever felt nauseated by eating porridge as a child, the chances are that you skip the oatmeal when you go out for breakfast decades later. Food aversions are deep, but they can form after a single unpleasant meal, according to experiments on rats.

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One of the curious features of personality change is that we are more profoundly altered by highly unpleasant experiences than by highly pleasurable ones, possibly because painful experiences signal imminent threats to survival.

Fear is a powerful motivator. This fact was revealed by animal behaviorists more than half a century ago in research that is ethically questioned today. In shuttle box avoidance, a dog learned that a light coming on at one side of the apparatus was a warning that the floor would be painfully electrified in 10 seconds. Subjects soon learned to jump over a low barrier to reach the safe side of the cage and received no more shocks.

Dogs easily mastered this avoidance task. Researchers now wondered how long it would take them to forget it. They continued the experiment as before but with the shock generator disconnected. To their amazement, the dogs continued to jump as they had when there was a risk of shock. After some 8,000 trials with nothing to report, the scientists reportedly got bored and packed it in.

Fear of physical harm is one important source of psychological problems. Fear of social rejection is less obvious but potentially just as important. A great deal of evidence suggests that corporal punishment, and scolding, make children turn out more aggressive and antisocial (3).

Interestingly, the effects of different kinds of unpleasant experiences on the brain are equivalent because they are mediated by the same stress hormones. Such effects involve alteration in brain anatomy and function (4,5). They include: intellectual stunting; delinquency, poor impulse control; lack of work motivation; and precocious sexuality (3).

It is as though a stressful childhood primes people to focus on immediate gains to themselves regardless of the consequences (3).

Implications for clinical psychology

Clinical psychologists are often called upon to help victims of extremely traumatic experiences move on with their lives. No one ever claimed that would be easy, and now we are beginning to understand why.

Some unpleasant experiences produce permanent changes in the brain and corresponding shifts in intelligence, emotional reactivity, happiness, sociability, and other traits that used to be thought of as set for life.

These personality shifts are generally considered pathological and that is undoubtedly true of post traumatic stress disorder, which ruins the lives of sufferers and their families. Yet, we need to recognize that many of these changes were useful to our ancestors in adjusting to risky environments.


1. Seligman, M.E. P. (1993). What you can change and what you can’t. New York: Fawcett Columbine.

2. Young, L. J., Murphy Young, A. Z., & Hammock, E. A. (2005). Anatomy and neurochemistry of the pair bond. Journal of Comparative Neurology, 493, 51-57.

3. Barber, N. (2009). From steroids to nation states: An integrated evolutionary approach to violent crime. Aggression and Violent Behavior, 14, 415-422.

4. Kalinichev, M., K. W. Easterling, P. M. Plotsky, and S. G. Holtzgman. (2002). Long-lasting changes in stress-induced corticosterone response and anxiety-like behaviors as a consequence of neonatal maternal separation in Long-Evans rats. Pharmacology Biochemistry and Behavior, 73, 131-140.

5. Teicher, M. H., Andersen, S. L., Polcari, A., Anderson, C. M., and Navalta, C. P. (2002). Developmental neurobiology of childhood stress and trauma. Psychiatric Clinics of North America, 25, 397-426.

Nigel Barber, Ph.D., is an evolutionary psychologist as well as the author of Why Parents Matter and The Science of Romance, among other books.


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