Abnormal Psychology

26 CHAPTER 1

medical model, once the biological causes are identifi ed, appropriate medical treat-

ments can be developed, such as medications. In fact, antibiotics that treat syphilis

also prevent the related mental illness, which was dramatic support for applying the

medical model to at least some psychological disorders.

Since that discovery, scientists have examined genes, neurotransmitters (chemi-

cals that allow brain cells to communicate with each other), and abnormalities in

brain structure and function associated with mental illness. However, explaining

psychological disorders simply on the basis of biological factors ultimately strips

mental disorders of the context in which they occur—in thinking people who live in

families and societies—and provides a false impression that mental disorders arise

from biological factors alone. As we shall see throughout this book, multiple fac-

tors usually contribute to a psychological disorder, and treatments targeting only

biological factors are not necessarily the most effective.

What biological factors might have contributed to the Beales’ unusual lifestyle

and beliefs? Unfortunately, the documentaries and biographies about the two women

have not addressed this issue, so there is no way to know. All we know is that one of

Big Edie’s brothers was a serious gambler, another died as a result of a drinking prob-

lem, and one of her nieces also battled problems with alcohol; taken together, these

observations might suggest a family history of impulse control problems. We might be

tempted to infer that such tendencies in this family refl ect an underlying genetic pre-

disposition, but we must be careful: Families share more than their genes, and com-

mon components of the environment can also contribute to psychological disorders.

The Modern Synthesis of Explanations

of Psychopathology

In the last several decades, researchers and clinicians increasingly recognize that psy-

chological disorders cannot be fully explained by any single type of factor or theory.

Two approaches to psychopathology integrate multiple factors: the diathesis–stress

model and the biopsychosocial approach.

The Diathesis–Stress Model

The diathesis–stress model is one way to bring together the various expla-

nations of how psychological disorders arise. The diathesis–stress model

rests on the claim that a psychological disorder is triggered when a person

with a predisposition—a diathesis—for the particular disorder experiences

an environmental event that causes signifi cant stress (Meehl, 1962; Monroe

& Simons, 1991; Rende & Plomin, 1992). Essentially, the idea is that if a

person has a predisposition to a psychological disorder, stress may trigger

its occurrence. But the same stress would not have that effect for a person

who did not have the predisposition; also, a person who did have a diath-

esis for a psychological disorder would be fi ne if he or she could avoid high-

stress situations. Both factors are required. For example, the diathesis–stress

model explains why, if one identical twin develops depression, the co-twin

(the other twin of the pair) also develops depression in less than a quarter of

the cases (Lyons et al., 1998). Because identical twins share 100% of their

genes, a co-twin should be virtually guaranteed to develop the disorder if

genes alone cause it to develop. But even identical twins experience different

types and levels of stress. Their genes are identical, but their environments are not;

thus, both twins do not necessarily develop the psychological disorder over time.

The diathesis–stress model is illustrated in Figure 1.3.

A diathesis may be a biological factor, such as a genetic vulnerability to a

disorder, or it may be a psychological factor, such as a cognitive vulnerability to

disorder, such as can occur when irrational or inaccurate negative thoughts about

oneself contribute to depression. The stress is often a social factor, which can be

acute, such as being the victim of a crime, or less intense but chronic, such as

recurring spousal abuse, poverty, or overwork. It is important to note that not

The bacterium Treponema pallidum is responsible

for the sexually transmitted disease syphilis.

Left untreated, syphilis eventually causes severe

brain damage that in turn gives rise to abrupt

changes in mental processes, including psychotic

symptoms.

Alfred Pasieka/Photo Researchers

1.3 • The Diathesis–Stress Model

According to the diathesis–stress model of

depression, people who are more vulnerable

to depression (high diathesis) will become

depressed after experiencing less stress than

people who are less vulnerable to depression (low

or absent diathesis). Put another way, given the

same level of stress, those who are more vulnerable

to depression will develop more symptoms of

depression than those who are less vulnerable.

Figure 1.3

T r w p w m t g g

hh hh ddll

High

High

Level of stress

Low

Low

Depression

Diathesis

absent

High

Minimal

Diathesis

present

Copyright © 1991 American Psychological Association