Chapter 2

How do nature and nurture, person and environment, individual and context interact to produce behavior?

How nature or nurture is really nature and nurture

Genetic variants provide one piece of the puzzle in explaining variation in human behavior

Virtually all behaviors are in part caused by genetic factors but this does not mean they are unchangeable

Upwards of 90% of the causal variance of autism is attributable to genetic factors.

However, early intervention and intensive treatment—environmental factors under the control of social work staff—can dramatically reduce the problem symptoms of autism.

Clients with actively involved parents and strong family and community supports constitute additional environmental strengths that can surmount various disabilities.

In other words, social workers have a host of clients who, they sense, present with some balance of biological, genetic, or neurological risks (and assets) coupled with environmental risks (and assets).

diathesis-stress model• Persons who are at genetic risk for some

disorder or condition are most sensitive to the stressors created by environmental risk

natural selection • Characteristics that facilitate the survival

and reproductive success of an organism persist whereas characteristics that do not facilitate the survival of the species desist.

genetic drift• Genetic evolution that is random and

neutral Mendelian disorder

• An inherited condition caused by a single genetic mutation

multifactorial phenotypes• phenomena caused by genes,

environments, and their interaction

heritability (h2) • a population statistic indicating the proportion

of variance in a phenotypic (or outcome) trait in a population that is attributable to genetic factors

shared environment (c2)• common environmental exposure that relates

usually to within-family characteristics nonshared environment (e2)

• source of environmental variation relates to circumstances that are unique to the individual even within the same family

polygenic• a trait or behavior caused by many genes

pleiotropic• individual genes that are associated with

multiple phenotypes alleles

• variants of a single gene genetic polymorphisms

• genes with different forms within a population

Personality• The trait of novelty/sensation seeking was

the first to be linked to a specific gene, the dopamine receptor known as DRD4.

• The 7-repeat allele of DRD4 has been shown to be associated with novelty/sensation-seeking personality traits

Associated with high levels of the personality trait of novelty seeking, which characterizes those who are impulsive, exploratory, fickle, excitable, and quick-tempered as opposed to reflective, rigid, loyal, stoic, slow-tempered, and frugal

Personality (Continued)• 7R allele of DRD4 has been linked to alcohol

abuse, binge drinking, and substance abuse generally

• The gene is also associated with ADHD

Diagnosis Heritability Range

ADHD 60–90%   Alcohol Dependence 50–60% Anxiety Disorder 40–50% Major Depression 40% Manic-Depression60–85% Schizophrenia 70–85%

Biosocial development starts at an early age

Maternal substance use is a direct, pernicious way that parents can cause neurological problems for their children.

Environmental risks, or pathogens, also exist in indirect broader contexts as well. For example, many toxins found in the environment have been shown to affect brain development and behavior.

It is important to note that heritable conditions are not exclusively related to antisocial behaviors, but also to other forms of maladaptive or unhealthy behaviors, such as obesity.

National Institute of Child Health and Human Development Study of Early Child Care and Youth Development found that children who were unable to delay gratification at age 4 were significantly more likely than children who could delay gratification to be overweight at age 11.

This relationship withstood controls for the child’s body mass index at age 4, maternal expectations of the child’s ability to delay gratification for food, and mother’s weight status, although the latter was also an important variable.

Neurogenetic factors continue to influence behavior during adulthood

A study of predatory and reactive murderers found that affective or reactive murderers had reduced prefrontal activity and increased subcortical (limbic) activity compared to controls.

Predatory murderers had similar prefrontal activity to controls but excessive subcortical activity.

These findings suggest that cold blooded killers are able to exercise neurocognitive control of their instincts despite excessive limbic activity, whereas hot-blooded killers are not.

The diathesis-stress model asserts that genetic risks are most sensitive to environmental risks for disorders and maladaptive behaviors.

A cell to society approach advances a biosocial framework where nature, nurture, and their interaction produce behavior.

Natural selection and neutral, random mutation are responsible for evolutionary changes in the human genome.

The central dogma of molecular biology articulates the ways that DNA is transcribed into RNA and ultimately translated into proteins and enzymes.

An inherited condition caused by a single genetic mutation is a Mendelian disorder, and these follow the laws of simple inheritance.

Variance in behavior is attributable to three sources: heritability, shared environment, and nonshared environment.

Behaviors that are caused by genes, environments, and their interaction are known as multifactorial phenotypes.

Genetic polymorphisms are genes that have different forms within a population, and the individual variants are called alleles.

More than half of human genes are expressed in the brain, and genetic variation gives rise to variance in neural substrates or pathways that relate to cognitive and behavioral functioning.

Gene–environment interactions occurring during gestation, infancy, childhood, adolescence, and adulthood shape human behavior.