Expert answer:The Behavioural Genetics of Predatory Criminal Beh
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since genetic propensities of the child may interfere with or not respond to
parenting efforts
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CHAPTER 7 The Behavioral Genetics of
Predatory Criminal Behavior
John Paul Wright University of Cincinnati
Kevin M. Beaver Florida State University
Even the most casual observer of science must be struck by the rate
at which new findings on human development and maladjustment are
published. Hardly a day passes in which the media do not report
startling results linking brain function to criminal behavior, or report
new relationships between specific genes and criminal traits. The
individuals who have led the way into this exciting, uncharted territory,
however, have not been sociologically trained criminologists.
Unfortunately, most criminologists remain on the disciplinary sidelines
or—even worse—remain wedded to an ideology that rejects genetic
influences in any form. This phenomenon may explain why “the
biological sciences have made more progress in our understanding of
criminal behavior in the last ten years than sociology has made over
the past 50 years” (Robinson, 2004, pp. ix–x).
While some criminologists may bristle at this declaration, there can be
little doubt that an explosion of knowledge on the development of
criminal conduct has occurred in recent decades, especially
knowledge about serious predatory conduct, and that the results have
been published in journals that feature studies on genetics and
biology. Not a single path-breaking study on criminal behavior has
been published in any leading criminology or sociology journal. Even
more telling is the fact that the leading criminological theories—that is,
social learning theory, strain theory, and self-control theory—all
require biological and genetic factors to be valid. Learning, for
example, occurs when connections are made between synapses in
the brain; stress and strain have been found to impinge on
hippocampus–pituitary–adrenal axes of the brain; and self-control
reflects a broader set of brain-based abilities known as executive
functions.
This chapter seeks to demystify the influence genes have on behavior
and serves to introduce the reader to a “biosocial” understanding of
predatory offending. In particular, it provides a brief introduction to
current knowledge regarding predatory offending, the fundamentals of
human genetics, the methods used by behavioral geneticists, and the
way in which this information is used to understand predatory human
behavior.
THE ROOTS OF PREDATION
Predation involves an intention to do harm to another, or at least a
willingness to actively seek out and injure another person. Predation
can be seen, for example, when armed robbers make a choice to
“hold up” an individual or commercial establishment, or when a rapist
takes the time to stalk his victim and then, when the risk of being
identified or caught is the lowest, commits his crime. Predation can
also be seen when a child molester seeks out and abducts a child
(Wright & Decker, 1997).
Even among criminals, predation in criminal conduct is unusual. Only
the most serious and habitual offenders are predatory. In contrast,
other offenders tend to be opportunistic or influenced by situational
contingencies, such as the presence of other criminals or the use of
drugs and alcohol. This is not to say that predatory offenders are not
also opportunists or that they do not commit crimes when under the
influence; rather, the key difference is that predatory offenders do not
require or are not driven by these concerns. To be direct, predatory
offenders are the truly criminal.
Research on the development of serious criminal conduct has
revealed three factors that are important in discerning the emergence
of predatory behavior. First, the warning signs for serious predation
are visible in infancy and childhood. Infants who are fussy, irritable,
and difficult to soothe, and who react negatively to novel situations are
significantly more likely to grow into children who have conduct
disorders and into adults with antisocial personality disorder (Caspi,
Roberts, & Shiner, 2005; Moffitt et al., 1996; Schmitz et al., 1999;
Shiner, Masten, & Roberts, 2003).
Second, traits related to later criminal conduct are also visible in
infancy and early childhood. While these traits have been labeled in a
variety of ways, they generally focus on the ability of the infant and
child to increasingly regulate his or her own behavior and to conform
to the social expectations found in varied environments. Impulse
control, self-regulation, self-control, emotional regulation, and
hyperactivity generally fall under this broad umbrella of traits.
Third, and most importantly, studies into the development of
aggression have found that its onset occurs around the time when
children gain mobility—that is, when they start walking and interacting
socially with other children. Richard Tremblay’s studies of very young
Canadian children, for example, found the peak age for aggression
was around 27 months; the same researcher also found that more
than 90% of young children had engaged in acts of aggression, such
as hitting, kicking, and biting, before 36 months of age (Tremblay,
2006; Tremblay et al., 2004; Vitaro, Brendgen, & Tremblay, 2002).
Physical aggression is a nearly universal human capacity that is
“normal” early in life, but becomes more uncommon in children over
time (Tremblay et al., 2004). Indeed, children who fail to “age out” of
the use of physical aggression by age 4 years are significantly more
likely to continue using physical aggression over long swaths of their
life-course. Perhaps not surprisingly, an early age of onset is one of
the strongest predictors of future adult predatory offending. Reviews
by Marvin Krohn and his colleagues (2001) found that early-onset
offenders committed 40% to 700% more crimes than individuals who
had an onset of problem behaviors later in life. Moreover, virtually
every predatory offender had experienced an early age of onset.
In summary, children who exhibit a variety of criminogenic traits, who
fail to gain sufficient self-regulatory capacities by age 4 years, and
whose behavior remains consistent across time and situation are at
substantial risk of developing into predatory adults. That this risk
trajectory materializes at such an early point in the life-course
necessarily hints at the likelihood that genetic factors are at play.
A BEHAVIORAL GENETIC
UNDERSTANDING OF PREDATORY
OFFENDING
How do we understand this set of empirical facts? With a few
exceptions, such as Moffitt’s developmental taxonomy, traditional
criminological theories remain silent on this issue, largely because
these theories of crime locate the causes of misconduct in
adolescence. Even if we broaden their theoretical lens and take a leap
of faith, criminologists would likely point to parental rearing
environments as the putative source of variation in young children’s
behaviors. But would they be correct?
Before answering that question, it is helpful to examine how a
behavioral geneticist would understand this issue. Behavioral genetics
is the field of study that analyzes how much variance in any given trait
or behavior is accounted for by genetic and environmental influences.
Behavioral genetic studies estimate this variance by analyzing
samples of monozygotic and dizygotic twins, relying on the laws of
genetics, and using sophisticated statistical models. At the heart of the
field, however, is the estimation of genetic and environmental
influences.
Figure 7.1 shows the hypothetical results of a behavioral genetic
analysis of some trait, such as impulsivity. In this pie chart, genetic
influences account for most of the variance in impulsivity (65%), while
nonshared environmental influences account for 25% and shared
environmental influences for only 10%. Estimates of genetic
influences are denoted by h2, which stands for the degree to which a
trait, characteristic, or behavior is heritable. The term “heritable”
should not be confused with “inherited.” Individuals “inherit” DNA that
will ultimately code for the creation of the brain, nervous system, and
arms and legs. By comparison, heritability reflects the degree to which
a complex trait can be influenced by genes. This distinction is critical
to understanding behavioral genetics because a person may be
endowed with a specific genetic propensity, such as toward
alcoholism or drug dependency, yet the propensity may never be
realized. Alcoholism in traditional Muslim countries, for example, is
very low because of the cultural prohibitions against alcohol use. Of
course, this does not mean that certain Muslims do not have a
propensity for addiction.
FIGURE 7.1 How behavioral genetics decompose the variance in
a trait.
Behavioral geneticists also specify that two types of environmental
influences are possible. Nonshared environments are those unique
experiences that make individuals more different than alike. Siblings,
even twins, often have different peer groups, for example. Thus
different peer groups represent a unique (nonshared) environment.
Shared environments, in contrast, are thought to make people more
alike. Children born to the same parents are exposed to similar broad
parental management strategies, for example.
Findings from hundreds of studies now show that virtually every
human trait and characteristic is genetically influenced. For certain
characteristics, such as vocational interests or religious orientations,
the influence of genes is very low. For other characteristics, especially
those associated with predatory offending, genetic influences
dominate (Plomin, Chipuer, & Neiderhiser, 1994). For example, IQ,
impulsivity, and self-control appear to be primarily genetic in origin
(Barkley, 1997). The same studies that have considered genetic
influences, however, also reveal that unique environmental
experiences usually outweigh the influences of shared environmental
influences—that is, shared experiences do not appear to make
individuals more similar, but instead highlight their differences (Plomin
& Daniels, 1987; Plomin, DeFries, McClearn, & Rutter, 1997; Plomin,
Owen, & McGuffin, 1994; Rowe & Plomin, 1981).
Would criminologists be correct in predicting that certain parenting
practices early in life will produce adult predatory behavior? The
behavioral genetic studies typically show that shared environments, or
the ways in which parents establish an overall home environment,
have little to no effect on their adult offspring (Wright & Beaver, 2005).
Does this finding mean that parenting has nothing to do with adult
predation? Not exactly. The processes that link parenting practices to
human development likely operate through biological mechanisms.
When rats lick their pups, for instance, the stimulation releases
oxytocin and prolactin, which are hormones that aid in the creation of
feelings of safety and love. Studies of Romanian orphans brought up
in horrific conditions have shown that these children possess reduced
levels of these hormones. Nurturance may thus help build a healthy
brain—at least for certain children. Some children may respond well to
nurturance; others may have no response at all. This is part of the
reason why it may be difficult to detect parental socialization effects.
The genetic propensities of the child may interfere with, or cause the
child not respond to, parenting efforts.
A Brief Note on Human Genetics
Humans inherit 23 pairs of chromosomes from each parent, one of
which is the sex-differentiating chromosome. Males receive a Y
chromosome from the father and an X chromosome from the mother
(XY); females receive an X chromosome from
both parents (XX). Chromosomes are made of deoxyribonucleic acid
(DNA). DNA, in turn, is composed of two elongated sections bonded
to chemical bases—the now-familiar double helix. The chemical bases
are adenine (A), thymine (T), guanine (G), and cytosine (C). Due to
their molecular structure, A can bond only with T, and G can bond only
with C, thereby forming what are known as “base pairs.” Genes, which
are embedded in chromosomes, are merely stretches of DNA with a
known arrangement of base pairs.
Current estimates place the number of genes in the human genome
between 19,000 and 25,000. This number is far less than the number
of genes found in other “lower-level” life forms, including some plants.
Nonetheless, Mendelian theory tells us that we inherit two copies of
each gene, one from the father and one from the mother. At one level,
Mendelian theory is correct: We do inherit our genes from our parents.
However, research has recently found evidence that for some genes,
humans may inherit more than just two copies; that is, one or both
parents may pass down more than one copy of particular genes.
Three international research projects found that at least 10% of all
human genes, or roughly 2900 genes, can vary in their number of
copies within an individual. Estimates that used to indicate that
humans were 99.9% genetically similar have since been revised to
state that we are approximately 99% genetically similar. This
restatement translates into a change from a 3 million base-pair
difference between humans to at least a 30 million base-pair
difference. It also means that it is even more likely that genes play a
significant role in serious, predatory behavior.
Even if multiple copies of some genes are present, they are not all
turned “on” or “off” at one time. The process whereby genes are made
active or inactive is called genetic imprinting. Genes, moreover, come
in different varieties. Differences in genes are called alleles. Allelic
variation occurs when mutations, genetic drift, cultural selection,
evolution, or any combination of factors alters a gene. For example,
the dopamine transporter gene DRD4 comes in several allelic
varieties, some of which are linked to an increased transmission of
impulsivity and attention-deficit/hyperactivity disorder (ADHD) (ArcosBurgos et al., 2004; Mill et al., 2002). Genes with various alleles are
referred to as polymorphic.
Individuals can demonstrate significant differences from one another,
even at the genetic level. Understanding the role of genes in complex
human phenotypes, however, is made even more complicated by the
fact that human genetic inheritance does not always follow Mendelian
genetic principles. According to these principles, human genetic
expression should follow a dominant and recessive form. Under most
conditions, dominant genes should be expressed. At one level, some
of our genes follow the dominant/recessive framework, such as the
genes for eye color. In contrast, for
complex traits, human genes do not appear to follow this principle.
Instead, functional human genes appear to follow a pattern of
incomplete dominance in their relationship to traits and behaviors.
Incomplete dominance refers to a situation in which the effects of
dominant and recessive alleles are blended and then expressed in a
phenotype.
How Do Genes Influence Predation?
Complex traits and behaviors are usually not produced by single
genes. Rather, multiple genes tend to act in concert to bring about
specific genetic potentials (Comings et al., 2001). The term “genetic
potentials” is appropriate here because genes create general
behavioral tendencies, or propensities, that can sometimes be
contingent on the environment for their activation. Recall the example
cited earlier in this chapter of the low alcoholism rate in traditional
Muslim countries. Clearly, some Muslims will have a genetic potential
to become addicted to alcohol, but that propensity will not materialize
if the individual never drinks. Single-gene influences are also typically
rather small, usually explaining less than 5% of the variance in any
complex behavior, such as violence. Research by Comings and his
colleagues has shown that genes have an additive influence on
ADHD, oppositional defiant disorder (ODD), conduct disorder, and
various personality dimensions. It appears that input from many genes
working in concert is required to produce traits and behaviors
(Comings et al., 2000a, 2000b, 2000c).
FIGURE 7.2 How the genotype influences predatory criminal
conduct.
How does this knowledge contribute to an understanding of serious,
predatory criminal behavior? Figure 7.2 provides an overview of the
respective influences genotypes have on predation. Because the
focus here is on genetic influences, the influence of environmental
variables is omitted. This omission is done for the sake of brevity and
because theory indicates that high-risk genotypes will experience
“faulty” development
regardless of their environmental setting—that is, for serious predatory
offenders, it is likely that their genotype confers so much risk that
environmental mediators and moderators will be rendered ineffectual.
Again, we are dealing with the truly criminal.
The first arrow in Figure 7.2 leads from the genotype to sex. In
studying predatory offenders, one overriding, consistent fact is
obvious: Predatory offenders are almost universally male. At one
level, being male is one of the best-known risk factors to criminal
involvement overall, but in terms of serious predation, males have the
market cornered. Of course, being a male is caused by the father
passing along Y chromosome to his offspring. The Y chromosome
contains the SRY gene, which causes the testes to form and drop in
the developing male fetus. This chromosome has only 78 genes,
which code for 27 proteins. All other chromosomes contain more
genes than the Y chromosome.
Once activated, the SRY gene signals the developing testes to flood
the brain with androgens, the most commonly known of which is
testosterone. Testosterone appears to “masculinize” the developing
male brain, leading to several effects. The first effect of this hormone
flood is that it creates what has been termed the “male brain.” The
male brain tends to excel in tests of spatial skills, the ability to focus
on an issue or problem, map reading, and mathematics and sciences;
it also shows a greater desire to seek risks and has 10% more area
dedicated to aggression (Baron-Cohen, 2002). The female brain, in
contrast, leads to individuals who are more religious, score higher in
tests of empathy and emotional recognition, score better on tests of
verbal skills, and test 60% to 70% better in memory for “locations and
landmarks” (Craig, Harper, & Loat, 2004).
The second effect of the high testosterone level in the developing
brain can be seen in the social behavior of males. Men are generally
more status oriented than women and ascribe to status hierarchies
more than women. Status hierarchies are also known as dominance
hierarchies. Dominance can be achieved through a variety of
methods, but the most efficient method—and the one employed more
frequently by males than by females—is violence. Dominance fueled
by testosterone may explain why overt physical aggression and
predatory behavior in men appears to fully materialize during
adolescence, a time when testosterone levels are 10 times higher and
when males add an average of 1 to 2 feet in growth and 100 pounds
of muscle (Booth, Granger, Mazur, & Kivlighan, 2006).
Brain Development and Functioning
The next arrow in Figure 7.2 leads from the genotype to brain
structure and functioning. The genotype spends a significant amount
of nuclear resources coding for the
development of the brain. Given that more than 60% of human genes
code for this one organ, it should come as little surprise that the brain
itself consumes significant amount of resources. Weighing in at 3
pounds, representing approximately 2% of total body weight, the brain
consumes roughly 10 times the amount of glucose as the rest of the
organs, and roughly 20% of the body’s oxygen intake (Robinson,
2004).
In terms of development, the human brain develops in a linear fashion:
from the simplest parts that control life-sustaining nonreflexive
activities, suc …
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