Natural Selection and Genes

When particular expressions of a characteristic are naturally selected and those expressions are associated with particular gene variants, those gene variants will be more likely than others to be passed on to future generations. For example, let’s say that there exists a gene with two variants, T and t, and that these variants are associated with difference in the average height of plants from a particular (fictional) species, Pirasus arizonensis. From a baseline height of five inches, T increases the average height by 1/2 inch, whereas t decreases the average height by 1/2 inch.

If P. arizonensis seeds are transported by birds into an environment in which the fully grown plant is surrounded by plants from another (fictional) species, Torensi mojavensis, that has an average height of six inches, the taller species will limit the smaller species’ access to sunlight. This, of course, would be detrimental to the survival and reproductive success of P. arizonensis. Thus, any P. arizonensis plant that grows taller than the average height of five inches will tend to survive longer and reproduce more.

Let’s say that the following 300 P. arizonensis plants have grown in this new environment:

100 TT plants, which will have an average height of 6 inches;
100 Tt plants, which will have an average height of five inches;
100 tt plants, which will have an average height of four inches.

The plants that are smaller than the surrounding plants will be much more likely to die before reproducing. And of course, other environmental factors also will affect plant survival, but in a more random fashion. Let’s say that 80 of the tt plants die before producing seeds, 50 of the Tt plants die before producing seeds, and 10 TT plants die before producing seeds. The result: 72% of the seeds in the next generation will contain T but only 28% will include t. Thus, if 300 plants grow in the next generation, their numbers will be as follows:

156 TT plants;
120 Tt plants;
24 tt plants.

As you can see, there are 276 plants with at least one copy of the T variant, which is much larger than the number of plants with at least one t variant (144 plants).

The third requirement of evolution by natural selection — the increased reproductive success of individuals with particular expressions of a characteristic —must remain stable over generations. This means that the “selective pressure” on P. arizonensis plants with respect to their heights must not change. The six-inch tall (on average) T. mojavensis plants must continue to limit the amount of sunlight obtained by smaller P. arizonensis plants. In this case, the following change in the frequencies of the T and t gene variants in this species should occur:

Figure 1. Changes in the Frequencies of T and t Over Five Generations.

As you can see, the frequency of T becomes almost 100% within five generations, which means that the population in this new environment now consists almost entirely of plants that are about six inches tall. Thus, over a very short period of time, natural selection can lead to a large change in the average expression of a characteristic in a population when individual differences in that characteristic are strongly associated with genetic differences.

Now, let’s return to the example from the previous post: the founding population of fruit flies on a tiny and isolated island buffeted by strong winds. Differences in the size of fruit-fly wings are strongly linked to differences in genes (Robertson & Reeve, 1952), to a degree similar to that described above for height differences in the fictional plant species. Thus, if the windy environment naturally select flies with smaller wings, gene variants correlated with smaller wings will increase in frequency over generations. This means that the population will evolve a smaller average wing size. This is shown in Figure 2 (the black bars represent the founding population and the white bars represent the population after a number of generations of natural selection for smaller wing sizes).

Figure 2. Evolution of a Population of Fruit Flies Undergoing Natural Selection for Smaller Wing Size

Although these two examples are fictional ones, there are many examples of natural selection and artificial selection (selection in which humans breed organisms that express particular characteristics). For introductions to and histories of the concepts of evolution and natural selection, see Colby (1996-1997), Endler (1986), and Zimmer (2001).

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Colby, C (1996-1997). Introduction to evolutionary biology (Version 2). Retrieved November 14, 2012, from

Endler, J. A. (1986). Natural selection in the wild. Princeton, NJ: Princeton University Press.

Robertson, F. W., & Reeve, E. C. R. (1952). Studies in quantitative inheritance. I. The effects of selection for wing and thorax length in Drosophila melanogaster. Journal of Genetics, 50, 416-448.

Zimmer, C. (2001). Evolution: The triumph of an idea. New York: HarperCollins.


The Evolutionary Approach in Psychology

In its most general sense, biological evolution refers to changes over generations in a population—changes in features of the body, mind, or behavior.

The evolutionary approach attempts to explain mind and behavior in terms of biological structures and processes that have evolved over hundreds to thousands of generations. This approach assumes that species have evolved ways of responding (cognitively, emotionally, and behaviorally) to environmental events because these responses led to greater survival and reproductive success in ancestral populations.

To take one example, the human spinal cord develops in such a way that it can rapidly process sensory information related to the temperature of objects. When we touch an object that is very hot, the spinal cord immediately activates a reflexive response that rapidly pulls the finger away from the object. Because this response occurs automatically, we can’t explain it as the result of conscious choice. In fact, the hand typically is jerked away before the information reaches the cerebral cortex (activity in the cortex is necessary for the conscious perception of pain). The existence of this spinal-cord reflex may be explained as the product of evolution: individuals that quickly pulled a body part away from painful stimuli were more likely to survive and, hence, reproduce because this proto-reflex prevented severe bodily damage. This explanation asserts that evolutionary changes in spinal-cord reflexes were caused by natural selection.

Evolution By Natural Selection

Evolution refers specifically to changes in the frequencies of variants of a characteristic (biological, psychological, or behavioral) over generations. A characteristic is a feature of an individual, such as eye color, that can be distinguished from other features, such as hair color. Characteristics often have variants that involve observable individual differences. For example, eye color has many variants, such as shades of brown, green, gray, and blue. Hair color also has many variants, such as shades of black, brown, red, and blonde. We will refer to such variants as expressions of the characteristic. Evolution, therefore, is a change over generations in the frequencies of expressions of a characteristic within a population of organisms. An analogous way of saying this is evolution is a change over generations in the average expression of a characteristic within a population of organisms. For example, a population consisting of 99% brown-eyed individuals and 1% blue-eyed individuals may evolve over generations into a population consisting of 1% brown-eyed individuals and 99% blue-eyed individuals. The average expression of eye color in this population evolved from brown to blue.

What causes evolution to occur in populations? For two decades beginning in 1836, Charles Darwin developed a credible naturalistic theory able to explain evolutionary changes — a theory that he began to develop when trying to interpret observations he had made during his five-year voyage on the H.M.S. Beagle (Darwin, 1839), as well as in research that he and others performed during the 23 years after Darwin returned from that voyage. This was the theory of evolution by natural selection. He published a detailed description of the theory in the first edition of the book, On the Origin of Species (Darwin, 1859; the sixth edition generally is considered to represent Darwin’s mature views on evolution and its causes.) No one before Darwin had so masterfully marshaled such an enormous amount of supporting evidence for the evolution of organisms. In addition, no one before Darwin had outlined such a compelling explanation of evolution: natural selection. Natural selection may be defined as the increased reproductive success of individuals with particular expressions of physical, mental, and/or behavioral characteristics. To put it most simply, Darwin argued that natural selection occurs when a subset of individuals in a population produce a greater number of offspring, on average, than others because they express a physical, mental, or behavioral variant that allows them to adapt better to their environments.

Let’s consider, for example, a fictional species of fruit fly that has just arrived on a windy and tiny island hundreds of miles from any other land. And let’s say that, in this founding population, there exists a a broad range of individual differences in wing size, as shown in the following graph.

Figure 1. The Percentage of Individuals in a Founding Population of Fruit Flies With Wings of Various Lengths

As can be seen in the graph, some individuals have large wings, which are advantageous for flying speed and for the ability to stay airborne, whereas others have small wings, which result in slower flying speeds and greater difficulties with staying airborne. On this small and windy island, larger-winged flies probably would be more likely to get blown out to sea, whereas the smaller-winged flies would be less likely to suffer that fate. Thus, smaller-winged flies would be more likely to survive long enough to reproduce than larger-winged flies.

This fictional example illustrates well the simple idea behind natural selection: individuals differ in their reproductive success because they have variants of characteristics associated with the ability to adapt to local environmental conditions. Because individuals with particular variants adapt better relative to individuals with other variants, the former survive longer, on average, and, hence, have more opportunities to reproduce. In other words, the local environmental conditions consist of factors that impose biological, psychological, and behavioral demands on organisms. These factors “naturally select” those organisms best able to deal with the environmental demands: they survive longer and reproduce more than others in their local population.

Given the obvious fact that natural selection occurs, how does it produce evolutionary changes in populations of organisms? There are three requirements that must be met in order for evolution in the average expression of a characteristic to occur through natural selection:

  1. There must be individual differences in the expression of the characteristic.
  2. These individual differences must be associated with genetic differences.
  3. The increased reproductive success of individuals with particular expressions of the characteristic must remain stable over generations.

The first requirement has already been discussed (see Figure 1). The second requirement involves the existence of genetic variants that affect the development of characteristics. A gene is the basic unit of biological heredity. Genes consist of sequences of chemical units (sections of DNA molecules) that are contained in chromosomes carried by the sperm of males and the ova (eggs) of females. In human reproductive cells (sperm and ova), there are 23 chromosomes, which together contain about 22,000 genes (Pertea & Salzberg, 2010). This means that, on average, each human chromosome contains about 1000 genes.

What Do Genes Do?

Genes influence the production of proteins and their use in developing and maintaining the body (for a history of the concept of the gene, see Rheinberger & Müller-Wille, 2010). For example, there are probably at least 16 genes that affect the development of eye color in humans (White & Rabago-Smith, 2011). But it seems that only two or three have major effects on individual differences in eye color. So, for purposes of explanation, let’s assume that there are only three genes that influence the development of eye color, which, for the sake of simplicity, we’ll refer to as Gene A, Gene B, and Gene C. As can be seen in the following table, babies receive one copy of each gene from their biological fathers (labelled as 1) and one copy of each gene from their mothers (labelled as 2):

Gene A has two variants: a brown variant and a nonbrown variant. If at least one brown variant is inherited from either parent, then, regardless of what is inherited at Gene B and Gene C, the person will develop brown eyes:

If, on the other hand, the nonbrown variant is inherited from each parent, then eye color is determined by what is inherited at Gene B and Gene C. Gene B has two variants: a brown variant and a blue variant. If at least one brown variant of Gene B is inherited from either parent, the person will develop brown eyes, regardless of what is inherited at Gene C:

If, on the other hand, the blue variant is inherited from each parent, the person will develop blue eyes depending on what is inherited at Gene C (which we will ignore for the moment):

Gene C has two variants: a green variant and a blue variant. If the blue variant of Gene B is inherited from each parent, then, if at least one green variant of Gene C is inherited from either parent, the person will develop green eyes:

If, on the other hand, the blue variant of Gene C is inherited from each parent, the person will develop blue eyes:

Thus, in our simplified example, eye color is determined by interactions among variants of three genes. The actual situation is much more complex: there are other genes as well as environmental factors that produce the many shades of eye color we see in real life.

Our example shows that gene variants, and interactions among them, contribute to the development of the physical characteristics of the body. In fact, you see evidence for this claim all around you: biological relatives often bear a strong resemblance to each other, as do conspecifics (members of the same species). Members of two closely related species typically don’t mate, and if they do, the mating typically doesn’t produce offspring. When interspecific matings are successful, however, the offspring generally express physical characteristics intermediate between the two species. For example, matings between male donkeys and females horses produce mules; and matings between male horses and female donkeys produce hinnies. Mules and hinnies have physical and behavioral characteristics that are intermediate between those of horses and donkeys. We’ll come back to this when we talk about matings between dogs and species that are closely related to them

The next post will look more closely at natural selection at the level of genes.

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Darwin, C. (1839). The voyage of the Beagle. Retrieved November 12, 2012, from

Darwin, C. (1859). On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life (6th ed.). Retrieved November 12, 2012, from

Pertea, M. & Salzberg, S. L. (2010). Between a chicken and a grape: Estimating the number of human genes. Genome Biology, 11, 206. doi:10.1186/gb-2010-11-5-206

Rheinberger, H-J, & Müller-Wille, S. (2010). Gene. The Stanford Encyclopedia of Philosophy. E. N. Zalta (Ed.). Retrieved November 12, 2010, from

White, D., & Rabago-Smith, M. (2011). Genotype–phenotype associations and human eye color. Journal of Human Genetics, 56, 5-7. doi:10.1038/jhg.2010.126
White & Rabago-Smith, 2011

Credulous Personality Disorder

Yesterday, I posted a piece in which I argued that scientific researchers must be inveterate skeptics and empiricists in their day-to-day work. In this post, I propose a new mental disorder for inclusion in the 5th edition of the Diagnostic and Statistical Manual. People lacking these essential scientific attitudes (i.e., skepticism and empiricism) may be suffering from this disorder. In fact, if the following ads from long ago make you wonder if such products now may be possible given advances in science and technology, you probably will meet the criteria for Credulous Personality Disorder.

The criteria for Credulous Personality Disorder were written several years ago, so this piece may need some updating; but the message is the same.


301.99 Credulous Personality Disorder

(formerly Pseudoneurotic Gullibility)

Proposal Submitted By Jeffry Ricker, Ph.D.
to the DSM-V Working Group

Diagnostic Features

The essential feature of Credulous Personality Disorder is a pattern of pervasive and excessive gullibility that causes the individual to accept without question claims unsupported by any credible evidence (including but not limited to claims involving health and health-related products, unconscious motivations, advertised products and services, extraterrestrial beings, get-rich-quick schemes, psychotherapeutic interventions, and/or the supernatural). This pattern begins by early adulthood and is present in a variety of contexts.

Individuals with Credulous Personality Disorder have a marked tendency to be easily convinced by evidence of poor quality, or even by no evidence at all, as long as the knowledge claim fits easily into the individual’s irrational worldview and is made by a person of authority (e.g., a guest on an all-night radio call-in show; a self-confident telemarketer with a British accent; a celebrity interviewee on The Tonight Show or a reporter for an entertainment magazine; a “therapist” appearing on a daytime talk show; an actor playing a doctor in a television commercial; an author of a book promoted by Oprah Winfrey; a “being” who claims to be from another planet or another dimension who channels through their next-door neighbor; anyone claiming to speak with the dead, nonverbal animals, or omniscient entities from another plane of existence).

The credulity of individuals with Credulous Personality Disorder seems to be driven most commonly by their desire for personal transformation, future well-being, or continued existence after death. In fact, people with this disorder typically dismiss claims supported by evidence of high quality whenever these claims contradict their hopes or cherished beliefs. This often causes them to spend large sums of money acquiring the latest product or service that seems to offer them hope and solace. Furthermore, much of their day is consumed with learning about and/or acquiring such products and services. In severe cases, the loss of jobs and close relationships or the experiencing of serious injury and even death result from the consequences of their rejection of well-supported claims (e.g., a person with malignant melanoma avoids the established medical treatment for this disorder and subjects him- or herself to a practitioner of Reiki).

Individuals with Credulous Personality Disorder tend to be trusting, friendly, and caring unless one of their core beliefs is subjected to critical analysis, at which point they often become defensive, indignant, and angry, although they may feign extreme concern for the happiness and well-being of the person questioning the belief (e.g., they may offer to pray for the skeptic). They often can be found in the self-help sections of bookstores discussing the latest works of Deepak Chopra or Andrew Weil. They typically express a compulsive stream of optimistic statements and aphorisms (e.g., frequently stating that they “cannot afford a negative thought”) and constantly discuss the newest miracle cure, diet fad, financial scheme, etc., that they believe will bring them life-long happiness and/or eternal bliss. These individuals often accumulate large amounts of debt because of their compulsive buying of items that offer the promise of health, financial success, self-transformation, etc.

Individuals with Credulous Personality Disorder often promote “alternative ways of knowing” that involve speculation, visialization, intuition, and shamanic journeys. They are easily convinced by subjective observations consistent with their beliefs and are highly suspicious of quantifiable measurements unless the latter seem to support their beliefs, at which point the evidence will be used in debates with skeptics long after it has been shown to be unreplicable and/or fraudulently obtained. Individuals suffering from this disorder may become psychologically distressed or physically ill when hearing the name of a prominent skeptic (e.g., someone who believes that he has been abducted by alien beings and anally probed passes out whenever Carl Sagan is mentioned; or a practitioner of therapeutic touch develops catalepsy and catatonic stupor whenever someone brings up the study by Emily Rosa and colleagues).

People with Credulous Personality Disorder may become so preoccupied with their credulous belief system that they seem unable to hear or remember the arguments of those with an opposing view. In fact, they often attribute statements to the skeptic that bear no relation to what he or she actually said. It is as if their minds become temporarily inactive whenever an opposing set of beliefs is described. Even when sufferers make an attempt to listen carefully to the views of skeptic, they may dissociate at critical points in the discussion (dissociative amnesia is a common comorbid disorder, although there is some evidence that this disorder itself is the product of extreme credulousness on the part of clinicians and clients).

Associated Features and Disorders

Individuals with Credulous Personality Disorder often experience extreme dysphoria because of their desperate and constant attempts to achieve total happiness, health, and self-fulfillment — attempts that always result in eventual disappointment. The dysphoria lifts temporarily when they find a new scheme for achieving these same goals. People with Credulous Personality Disorder often are diagnosed with comorbid Anxiety Disorders, Dissociative Disorders, Somatization Disorder, Major Depression, Dysthymic Disorder, Substance-Related Disorders, Disorders of Impulse Control, as well as other Personality Disorders, especially Dependent Personality Disorder, Avoidant Personality Disorder, Histrionic Personality Disorder, Borderline Personality Disorder, Narcissistic Personality Disorder, and several other personality disorders still under development (see future editions of this manual).

The likelihood of developing Credulous Personality Disorder is increased if the individual, during childhood, ever celebrated a major holiday in which mythical figures were said to deliver presents or candy to good girls and boys, heard an “urban myth” while sitting around a campfire on a cold and moonless night, attended a religious service, was tempted by advertisements for X-ray glasses, had close relatives who voted for Richard Nixon, watched professional wrestling, bought “sea monkeys,” attended a public school focused on raising students’ self-esteem, bought tickets to a concert performed by a “teen idol,” had a parent who subscribed to Reader’s Digest or TV Guide, thought that the “Fonz” was cool, cried for days after watching Old Yeller, bought cereal in order to obtain the prize inside, watched television more than five minutes per day, or ever ordered anything advertised in the back of a comic book.

Specific Culture, Age, and Gender Features

The prevalence of Credulous Personality Disorder does not seem to be associated with any specific cultural, age-related, or gender-related factors.

Nevertheless, the specific symptoms exhibited do seem to be influenced to some extent by these factors. With respect to culture, the symptoms of Credulous Personality Disorder reflect the beliefs common in the culture in which the person was raised (e.g., Americans are more likely to believe that they will become rich if they cash in their life savings and buy thousands of Powerball tickets). In addition, the specific symptoms change with age. For example, children are more likely to believe that, if they step on a crack, they will break their mother’s back whereas adults are more likely to believe that, if they take megadoses of Vitamin C, they will never again suffer from a cold. Lastly, there seem to be some gender differences in symptomatology, especially when the beliefs involve sexual behaviors. For example, men are more likely to believe that, if they honk their horn and hoot loudly from their car window at an attractive female, she will probably sleep with them. Women are more likely to believe that, if they sleep with a man, he probably will marry them.


The lifetime prevalence of Credulous Personality Disorder has been reported to be between 0.1% and 99.9% in the general population, but it is not known whether such reports can be trusted since there is evidence to suggest that a large number of these studies were performed by researchers suffering from the disorder. At present, it seems safe to say that the disorder is very common in the general population (perhaps approaching 100%). The severity of the symptoms, however, differ dramatically across individuals. It seems that the disorder is very common in both in-patient psychiatric settings and out-patient mental-health clinics, but it rarely represents the presenting disorder. Many clinicians also suffer from Credulous Personality Disorder, which makes diagnosis and treatment of the disorder very difficult. These clinicians not only tend to believe the overly credulous pronouncements of their clients, they also are much more likely to believe that untested or falsified treatment modalities actually work (such as eye-movement-desensitization-and-reprocessing therapy, or any therapy in which repressed motivations or dissociated memories induced by trauma are used as explanations of problematic behavior).


In almost all cases, Credulous Personality Disorder has a chronic course. Few remissions of symptoms have been observed in people who are fully or partially conscious. In the few cases of recovery that have been reported, there is reason to suspect that the reporting clinicians were suffering from the disorder and, thus, the accuracy of their reports can be questioned. The symptoms tend to become more severe when the individual is experiencing mild to severe stressors, and even when no stressors are being experienced at all. The symptoms also tend to become more severe after the individual has had experiences designed to encourage a lack of skepticism (e.g., after watching television infomercials, after listening to an audiotape of any lecture by Anthony Robbins, or while attending a talk at a local Unitarian church, especially if that talk is related to Jungian psychotherapy). The symptoms remit completely only during coma or upon death.

Familial Pattern

There is some evidence for an increased prevalence of Credulous Personality Disorder in the first-, second-, third-, fourth-, and nth-degree relatives of probands with the disorder.

Differential Diagnosis

Credulous Personality Disorder is not easily distinguished from Schizophrenia, Schizophreniform Disorder, Schizoaffective Disorder, or any other psychotic disorder in which delusional thinking is prominent. In fact, in many cases, people with Credulous Personality Disorder report hallucinatory experiences consistent with their beliefs (e.g., seeing the faces of supernatural entities in taco shells or stained toilet-seat covers). Their speech often suggests the existence of formal thought disorder, especially when trying to justify their beliefs to skeptics. At this time, there is no general consensus regarding the distinguishing characteristics of Credulous Personality Disorder with respect to Psychotic Disorders. Most clinicians agree that there is a great deal of overlap between the symptoms of Credulous Personality Disorder and Delusional Disorder. In fact, some believe that the two disorders exist on a continuum of severity, but are not certain which disorder is the more severe.

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Skepticism and Empiricism

One of the major goals of this website is to help people learn about scientific research in psychology and how it can help all of us to better understand why we do what we do in our everyday lives. This goal requires that we learn about some of the attitudes and assumptions indispensable to doing good research in the behavioral sciences. In this post, I will argue that two essential attitudes for scientific researchers are skepticism and empiricism. In fact, these attitudes form the foundation of the scientific approach to understanding ourselves and the world around us.

Evaluating Claims About Mind and Behavior

Angel Therapy works on the belief that everyone has guardian angels, and these angels perform God’s will of peace for us all. When we open ourselves to hear our angels’ messages, every aspect of our lives become more peaceful…. You can connect with your angels and guides. According to the therapy, everyone has at least 2 guardian angels, and a variety of spirit guides, souls who have agreed to work with you throughout your life. These angels and guides are loving entities, and are here to help you in every aspect of your life. They are believed to be the source of intuition and inspiration, and there to support you during times of need. (Quoted from The Body Guide website)

Three main claims are made in this passage. (1) We all have at least two guardian angels as well as countless other angels and spirit guides that we can “connect with.” (2) These supernatural beings want to help us in every aspect of our lives. (3) This help can be therapeutic: it can reduce or eliminate psychological problems and even provide “intuition and inspiration.”

But what is the evidence that these supernatural beings actually exist and that, if they do, that they want to help us? Susan Stevenson, a therapist, has claimed that the evidence is all around us, but that we need to pay close attention to see it:

My life seems to be teeming with angelic connections, and the momentum is building. Have you noticed this in your own life? Angelic reminders that they are with us- ‘whispers’ in our ear, ‘taps’ on the shoulder, brushes of air across your skin or changes in air pressure, ‘flutters’ from deep inside, glints of light and color- all these gentle hints to pay closer attention to their presence. Think back- have you been paying attention, listening, responding? (Carroll, 2012)

When one makes a claim, one is stating that something is a fact. In other words, a claim is a statement that is thought by at least one person to be true; but of course, it may turn out to be false. Claims often involve interpretations of experiences. For example, you may interpret a “brush of air” across your skin as an angel who has just passed by, or you may interpret it as a breeze that has wafted through the room from an open window. A glint of light may be the sign that an angel is nearby, or it may be the sign that sunlight just reflected off a passing car. In other words, two people may interpret the same experience in different ways. In deciding which interpretation is more likely to reflect reality, we need to evaluate the different interpretations. We do this by examining relevant evidence.

In your everyday life, you probably often have heard claims made about psychological problems and psychological therapies; and you probably think that you already know quite a bit about psychology. In order to get a sense of what you might know, please take the following brief quiz.

Which of the following claims are true?

  • dream images are known to have particular meanings that involve unconscious desires and conflicts
  • eating sugar causes children with attention-deficit hyperactivity disorder to become even more hyperactive
  • a person who commits suicide must have been clinically depressed
  • a 40-year-old man who has sex with a 15-year-old girl would be diagnosed with pedophilia
  • there are more admissions to mental hospitals during full moons than at other times
  • unconscious memories of traumatic events can be remembered in detail with hypnosis
  • a person who exhibits two or more personalities is diagnosed with schizophrenia
  • low self-esteem is known to cause most self-destructive behaviors
  • most mental disorders can be cured by remembering and mentally reliving distressing past experiences

You may be surprised to learn that none of these claims is known to be true. In fact, all but a few are known to be false, and the remaining ones are controversial at best. In order to avoid basing important decisions on false claims, clinicians (professionals who study and treat psychological problems), or those who aspire to be clinicians (perhaps you), need to learn to think critically about claims made about psychological problems and their treatments. Of fundamental importance to this goal is the development of skeptical and empirical attitudes regarding claims.


In some religions, a shaman is said to be a mediator between the visible natural world and an invisible supernatural world. The shaman claims to be able to journey to the supernatural world in order to help heal the ill, foretell the future, and control natural events. Some mental-health workers use shamanic journeying to help those suffering from psychological problems. Sharon Van Raalte (1998) gave an example of her shamanic work with a client:

Through image and symbol, the shamanic journeys revealed levels of knowing that were often beyond what could be perceived or expressed by the clients or the psychiatrist. For example, Luke was dying from a brain tumor. An early journey suggested that I teach his wife, Suzanne, to work with him. Learning to journey to find her power animal proved to be helpful when it came time for her husband to die. At another point, I was journeying on a question for myself, when the focus abruptly changed. I found myself sitting with [Luke and Suzanne] in a boat that began moving to a farther shore. On the other side, Luke got out of the boat and went toward a group of people waiting to greet him. I had the sensation that the pain they had caused him in his life was washed away as they surrounded him with love. The classic shamanic experience (known as conducting the souls of the dead) had come unbidden. (p. 164)

In other words, Van Raalte claimed that she and Suzanne had accompanied Luke to the “other side” as he was dying, and then saw him being reunited with others who had died before him. An apparent confirmation of this interpretation came later:

Only after I had reported this journey to the psychiatrist did I learn what had literally happened. In his delirium as he was dying, Luke had called out the name of his dead sister, with whom he had had a painful relationship. Drawing from the experience of her single [shamanic] journey, Suzanne knew what he was seeing and urged him to run to his sister. (p. 164)

In these passages, Van Raalte is making a number of claims: (1) She is able to journey to a spirit world. (2) She saw Luke being reunited with his dead sister. (c) Shamanic journeying is an effective treatment for at least some psychological problems. When hearing claims such as these, scientific psychologists are trained to be skeptical–to doubt the claim unless it is supported by adequate evidence. These particular claims may be true, but we need to see good supporting evidence before we accept them. As an ideal, we should be skeptical of any claim that may have an important impact in our lives, even a claim that seems on its surface to be convincing. It probably is impossible to reach this ideal, but we should strive to develop our skepticism as much as we can in order to improve our decision-making and problem-solving abilities. And it should be incumbent upon people who work in mental-health fields, especially those offering therapeutic services, to develop their skepticism as fully as they can since their beliefs and actions have important consequences for those with psychological problems.

When confronted with a claim, a skeptical thinker needs to do two things. First, because a claim is based on a particular interpretation of an experience, a skeptical thinker always needs to consider other possible interpretations of that experience. For example, a shamanic therapist who claims to be journeying to a supernatural realm may actually be doing so. On the other hand, she may only be vividly imagining that she is doing so, or she may be experiencing hallucinations. By considering other interpretations, a skeptical thinker is less likely to automatically accept the claimant’s interpretation and more likely to examine carefully the various alternatives.

Second, a skeptical thinker needs to determine if there is any evidence that contradicts the claim. For example, Van Raalte stated that she saw Luke being greeted by a “group of people,” all of whom had caused him pain during his life. However, the psychiatrist with whom Van Raalte worked stated that, at the time of his death, Luke mentioned only his sister’s name and was urged to run to his sister. This evidence seems to contradict the claim made by Van Raalte that she had seen Luke with a group of people at the time of his death. Without further clarification and more evidence, it is difficult to know whether to accept or reject her claim.


Evidence consists of observations that allow us to evaluate whether a claim is likely to be true or false. Let’s consider a very simple claim that probably everyone believes is true: “The sun will rise tomorrow morning.” For me, this claim is based on the following evidence:

  • As far back as I can remember, I have seen the sun rise each and every morning of my life.
  • No mention has ever been made in any historical document that the sun has ever failed to rise. It seems likely that something as significant as the sun not rising would have been recorded and reported.
  • Scientists and other experts tell us that the sun rises each morning because the Earth rotates on its axis, and that it should continue to do so for billions of years.

From all this evidence, it seems reasonable to infer that the sun will rise tomorrow morning. If someone claimed that he knew that the sun was not going to rise tomorrow morning, you would immediately ask him why he believed this claim (this is equivalent to asking him for his evidence). If he stated that he dreamed that this would happen and that his dreams often come true, most of us would be skeptical: the supporting evidence (his dream) does not seem adequate to accept his claim.

What is the best kind of evidence for supporting a claim? Should we rely upon what an expert tells us? Should we accept a person’s intuition? Are the statements of a channeled spirit guide acceptable evidence for a claim? Regarding the nature of evidence, scientific psychologists are trained to be empirical–to make direct observations of events in the natural world that are relevant to evaluating the claim. Empiricists do not consider statements made by authorities, armchair speculations, dream interpretations, or messages supposedly obtained from supernatural beings, to be adequate evidence for a claim. Instead, empiricists must see for themselves whether a claim is likely to be true or false. For example, in testing the claim that shamanic journeying is an effective treatment for at least some psychological problems, an empiricist would want to measure directly the severity of clients’ symptoms both before and after being told what was discovered about them during a shamanic journey. If their symptoms improved relative to those of a second group of clients who were told things about themselves that were not discovered during a shamanic journey, then this would be evidence that shamanic journeying (for whatever reason) is an effective therapeutic technique.

You may contact me at


Carroll, R. T. (2012). Angel Therapy. The Skeptic’s Dictionary. Retrieved November 9, 2012, from

The Body Guide. (2012). What is Angel Therapy? November 9, 2012, from

Van Raalte, S. (1998). Direct knowing. In W. Braud & R. Anderson (Eds.), Transpersonal research methods for the social sciences (pp. 163-166). Thousand Oaks, CA: Sage Publications.

Co-Self-Dependent No More: Ending the Nightmare of Self-Enmeshment

I’ve been giving it a lot of thought lately, and I’m starting to think that maybe I’m not the best person for me. I’m beginning to realize that I don’t bring out the best in myself, and that probably I stay with myself mostly out of habit. No, that’s not it. It’s like an addiction: you know that it’s really going to be bad for you over the long-term but that, just for this moment in time, you’re going to give in to the cravings; knowing deep down that it won’t be just for this moment–that it won’t stop until you’re dry-heaving in the back of an old station wagon with faux wood paneling, hating yourself for allowing yourself into your life and letting it happen all over again.


So then you go cold-turkey for a while, promising yourself that it’s never going to happen ever again: that you’re never going to be you again. But the cravings are there–those God-damned cravings–and they build and build until it gets so bad that you eventually end up right back where you started: getting together with yourself, “just for tonight,” and starting that roller-coaster ride all over again. Doing it again and again until you can’t stand the sight of yourself in the mirror anymore. And the crazy thing is that you know … YOU KNOW! … just before you open that door and invite yourself back into your own life, how it’s all going to end: the same way it’s ended a 1000 times before. But you open that damned door anyway!

My relationship with myself has always been a wild, up-and-down roller-coaster ride. Sometimes it’s really great: I’m a lot of fun to be with, I’m feelin’ really close to myself–the bond is there and it’s really strong. It’s no effort at all to be with myself, to get along, and just to feel comfortable being me with myself–no judgments and no expectations. Hell, at those times, I feel such a strong connection with myself that I even find myself finishing my own sentences; and just, you know, really, really understanding where I’m coming from. At those times, I feel as if I’ve known myself my whole life–like I’ve grown up with myself, sleeping in the same crib, playing with the same friends, going to the same schools, even lusting after the same people … you know, experiencing everything, and I mean EVERYTHING, together. It’s such a high to feel this way–to be understood so well by yourself. Nothing’s hard, nothing’s difficult. And, at those times, I just couldn’t imagine ever being without myself.

But then it starts. I do something a little stupid and get annoyed with myself. It’s just a minor thing, a little irritation; but I feel hurt and betrayed anyway, and just so very upset that I could treat myself that way, after all I’ve been through with myself! I know that I’m over-reacting at those times but I can’t help it! After the great times, it’s such a shock to see myself treating myself this way. So, I start to distance myself, more and more, until eventually It turns into a big fight, and I refuse to even think to myself for a few days.


But of course, that doesn’t continue for long. Eventually I start to think again. And, over all the years I’ve been together with myself, my life has become so intertwined with my life that it seems impossible to even imagine living apart from myself. When I think those thoughts, it seems just too damned difficult to take that final step and break it off for good! You know, I really hate to admit it but, at those times, I feel like I’m nothing without myself and that I’ll never be anything unless I’m always in my life. (God, it was so hard to write that sentence, and it’s even harder to reread it now. Give me a minute, will you?)

It’s my own fault that I think this way, I know. I’ve let myself believe what I tell myself is true. When I believe that something is true, I can’t bring myself to disagree with myself, or at least to question whether or not it’s possibly, just possibly, not true. It’s like I have this mysterious power over myself–a power that I can’t describe but that I’ve never been able to resist. I know that none of what I’m thinking–you know, that “I can’t survive unless I’m in my life,” that “I’ll die if I leave myself,” all that crap that I’ve been telling myself for years–I know that none of it is true! But, just when I’m at a place where I can begin to question it, all of a sudden I’m there, and all my rational thinking flies out the window. I tell myself that I’m crazy, that it IS true that I can’t live without myself, and I’m stuck again!

Hell, it makes me disgusted with myself just to admit it, but I find that I can’t even go to the bathroom without myself!! Now how sick of a relationship is that??? So, I pretend like none of the bad stuff ever happened, that I’m really a great guy, that everything is going to turn out all right, that I never really meant to hurt myself that way. In short, I forgive myself despite the years of betrayals and all the hurt I’ve caused myself.

You know what’s nuts? Underneath it all, when all is said and done, I KNOW that I’m just using myself, that all I’m doing is using myself to get my own needs met. But I let it happen anyway. Why? Well, because … because it’s just so easy to say “yes” to myself. I’m completely, utterly, under my own control, it seems. I have absolutely no boundaries with myself! I just come waltzing right back into my life as though nothing’s happened! I hate myself for loving myself so much, because I know that it’s not a real love–a healthy love!! It’s a toxic, sick, disgusting “love”–a love where I let myself use myself to satisfy my own needs.

And when I let myself back into my life, I know that it’s all going to start and end just like it has so many times before; and that it will do so again, and again, and …. well you know. You’ve been there, too.

But I think that I’m finally through with it! Today, no matter what I did in the past, I’m going to take charge of my own life and never let me back into my life again! EVER!! I know that I’m bad for myself, that I keep myself down, that I’ll never grow as a person as long as I keep letting myself back into my own life. So, I’ve decided that, starting from this point on, I’m making this unbreakable commitment to myself. I’m telling everyone I know so that I will never go back on it.

I will never, ever again allow myself to be me!!

Classical Conditioning of Drug Tolerance

In the case of psychoactive drugs, drug tolerance is a condition in which repeated use of a drug leads to reductions in its psychological effects, thereby requiring progressively larger doses in order for similar effects to occur. Many factors affect the development of drug tolerance, and learning is one of them. A classic study by Siegel, Hinson, Krank, and McCully (1982) was one of the first to demonstrate this. The researchers found that rats can be classically conditioned to develop tolerance to heroin.

Siegel, et al. (1982) wanted to understand why some addicts died after taking a dose of the drug that they had taken many times before. The official cause of death in these cases usually was said to be a “drug overdose” because the dose was high enough to kill most people not addicted to the drug. These addicts, however, had developed a high level of tolerance to the lethal effects of the drug, so ascribing their deaths to an overdose couldn’t be correct.

The researchers hypothesized that the addicts’ tolerance was due, in part, to classical conditioning. That is, the situation is which they typically took the drug had become a conditioned stimulus (CS) that elicited a conditioned response (CR) involving a change in biological processes that prepared their bodies to counteract the lethal effects of the drug. This explanation may be easier to understand by looking at a case study described in Siegel (2001). The study was of a man suffering from severe pain because of pancreatic cancer. In order to reduce the pain, he received four injections of morphine per day. Over time, the dosage had been increased to a high level because of the tolerance he had developed to morphine’s pain-reducing effects.

The patient stayed in his bedroom (which was dimly lit and contained apparatus necessary for his care), and received injections in this environment. For some reason, after staying in this bedroom for about a month, the patient left his bed and went to the living room (which was brightly lit and different in many ways from the bedroom/sickroom). He was in considerable pain in the living room, and, as it was time for his next scheduled morphine administration, he was administered his usual dose of the drug. The patient quickly displayed signs of opiate overdose (constricted pupils, shallow breathing), and died a few hours later. (p. 510).

The explanation given by Siegel and his colleagues involved the classical conditioning of tolerance to the lethal effects of morphine. The explanation is outlined in Figure 1:

Figure 1. Classical conditioning of tolerance to morphine

As shown in Figure 1, the stimuli in the bedroom comprise a CS that produces a CR consisting of physiological changes that counteract the effects of morphine (i.e., are opposite to the physiological changes caused by morphine). This CR is part of the change in biological processes that causes tolerance to drugs, thereby requiring people to use higher doses in order to experience the same psychological and physical effects of drugs. The CR develops because the CS is followed by the drug, which can be thought of as a UCS — in this case, the injection of morphine. The UCS causes a UCR consisting of physiological changes associated with the drug. By counteracting the physiological effects of the drug, the CR reduces its lethality (i.e., the probability that the drug will result in death).

When an addict takes a high dose of a drug in a different environment — in the case of the man taking morphine, the different environment was his living room — the CR does not occur and, therefore, the drug now has its full effect on the body, which makes it more likely that the person will die.

Siegel, et al. (1982) designed an experimental study to test the classical-conditioning theory of drug tolerance. They gave rats injections of heroin every other day for 30 days (a total of 15 injections). They increased the dose gradually over time so that the rats eventually could tolerate relatively high doses. On the days the rats didn’t get heroin,they were injected with a sugar solution (see Table 1 below).

Siegel, et al. (1982) tested two heroin-injected groups:

  1. Group 1. These rats received their heroin injections in Room 1, which was the room that housed all the rats (the “colony room”). They received their sugar injections in Room 2, which was a room that differed from Room 1 in two ways: (a) no rats were housed there;(b) a machine generated constant “white noise.”
  2. Group 2. These rats received their heroin injections in Room 2, and their sugar injections in Room 1.

The researchers also included a placebo-control group (Group 3) that received injections of the sugar solution in both Room 1 and Room 2 on the same schedule as the other rats. Table 1 shows the schedule for each group on the first four days of the 30-day experiment.

Table 1. The schedule of heroin and sugar injections over the first four days of the experiment

At the end of the 30-day period, rats in all three groups were given a very large dose of heroin (almost twice as much as those in Group 1 and Group 2 had received before). Figure 2 shows the results.

Figure 2. Mortality in heroin-tolerant and control rats after receiving a very high dose of heroin

The label Different in Figure 2 refers rats in Groups 1 and 2 that received the very large dose of heroin in the room in which they had been injected with the sugar solution during the first part of the experiment. The label Same refers to in Groups 1 and 2 that received the very large dose of heroin in the room in which they had been injected with heroin during the first part of the experiment. The label Control refers to rats that were injected only with the sugar solution during the first part of the experiment.

As can be seen in Figure 2, almost all the rats in the Control Group died after being injected with the large dose of heroin because they had no tolerance for its lethal effects. About 64% of rats in the Different condition died, whereas only 32% of the rats in the Same condition died. Siegel, et al. (1982) interpreted these results as supporting their theory: the environmental stimuli in which drug addicts usually take the drug serve as a CS that produces a CR that increases tolerance for the drug’s effects.

The researchers concluded that the sensory stimuli from the room in which the rats were injected with heroin made up a CS. The rats developed a CR to that room–a CR consisting of changes in biological changes that counteracted the effects of the drug they were about to receive. When they received the final injection in a different room, the CR didn’t occur, which increased their chances of dying from the overdose.

Another point I want to make is that, although in most experimental studies of classical conditioning, the CR and UCR are the same or very similar, the responses also may be very different. In fact, in the study by Siegel, et al. (1982), the CR and UCR were completely opposite from each other.


Siegel, S. (2001). Pavlovian conditioning and drug overdose: When tolerance fails. Addiction Research & Theory, 9, 503-513. doi: 10.3109/16066350109141767
Retrieved October 18, 2011, from

Siegel, S., Hinson, R. E., Krank, M. D., McCully, J. (1982). Heroin “overdose” death: Contribution of drug-associated environmental cues. Science, 23, 436-437.  doi: 10.1126/science.7200260

Experience and the Other-Race Effect

The other-race effect is the reduced ability to recognize strangers’ faces of another race relative to strangers’ faces of one’s own race. Many studies have demonstrated the reliability of this effect  (see Meissner & Brigham, 2001, for a review).  And a number of studies suggest that experience beginning in infancy is important for the development of the other-race effect (e.g., Bar-Haim, Ziv, Lamy, & Hodes, 2006). In short, beginning in the first year of life, children gradually become better at recognizing faces of those belonging to the race (or races) they most frequently interact with and gradually lose the ability to recognize faces of those belonging to other races.

Some researchers have tested the claim that the other-race effect depends on early experience by exposing young children to other-race faces. For example, Heron-Delaney, Anzures, Herbert, et al. (2011) noted that Caucasian children typically begin to develop the other-race effect between the ages of 6 and 9 months. Thus, they had parents periodically show their infants pictures of Chinese faces during this time. The researchers found that, even though the total amount of exposure to Chinese faces over the 3-month period was only about 70 minutes, these infants were able to recognize Chine faces as well as Caucasian faces, whereas infants not exposed to Chinese faces during that time showed the other-race-effect.

Some research suggests that early-childhood experiences may not have permanent effects on other-race facial recognition. One study found that adults of Korean origin who, between the ages of 3 to 9 years, moved to France, Switzerland, or Belgium after being adopted into Caucasian families were better at recognizing Caucasian faces than Asian faces (Sangrigoli, Pallier, Argenti, Ventureyra, & de Schonen, 2005). The researchers concluded that, because these individuals experienced primarily Caucasian faces in later childhood, not only was the other-race effect eliminated for them, it was reversed.

Another study, however, found that Chinese and Vietnamese children (6 to 14 years of age) adopted into Caucasian families in Belgium between the ages of 2 and 26 months recognized Caucasian and Asian faces equally well (De Heering, De Liedekerke, Deboni, & Rossion, 2009). In other words, experience with Caucasian faces eliminated the other-race effect but it did not cause a reversal of the effect.


Bar-Haim, Y., Ziv, T., Lamy, D., & Hodes, R. M. (2006). Nature and nurture in own-race face processing. Psychological Science, 17, 159-163. doi:10.1111/j.1467-9280.2006.01679.x

De Heering, A., De Liedekerke, C., Deboni, M., Rossion, B. (2009). The role of experience during childhood in shaping the other-race effect. Developmental Science, 13, 181–187. doi:10.1111/j.1467-7687.2009.00876.x

Heron-Delaney, M., Anzures, G., Herbert, J. S., Quinn, P. C., Slater, A. M., Tanaka, J. W., et al. (2011). Perceptual training prevents the emergence of the other race effect during infancy. PLoS ONE 6(5), e19858. doi:10.1371/journal.pone.0019858

Meissner, C.A., & Brigham, J.C. (2001). Thirty years of investigating the own-race bias in memory for faces: A meta-analytic review. Psychology, Public Policy and Law, 7, 3–35.

Sangrigoli, S., Pallier, C., Argenti, A.-M., Ventureyra, V. A. G., & de Schonen, S. (2005). Reversibility of the other-race effect in face recognition during childhood. Psychological Science, 16, 440-444. doi:10.1111/j.0956-7976.2005.01554.x