Chapter 3
Biological Foundations: Genes, Temperament, and More
Chapter Outline
BIOLOGICAL FOUNDATIONS: GENES, TEMPERAMENT, AND MORE
BIOLOGICAL PREPAREDNESS FOR SOCIAL INTERACTION
HOW ARE BABIES PREPARED?
From Biological Rhythms to Social Rhythms
Visual Preparation for Social Interaction
Auditory Preparedness for Social Interaction
Smell, Taste, and Touch
Beyond Faces and Voices: Primed to be a Social Partner
WHY ARE BABIES PREPARED?
THE NEUROLOGICAL BASIS OF SOCIAL DEVELOPMENT
The Brain
Brain Growth and Development
Hemispheric Specialization
Neurons and Synapses
Brain Development and Experience
Mirror Neurons and the Social Brain
GENETICS AND SOCIAL DEVELOPMENT
Bet You Thought That . . . Genes Determine Your Potential
METHODS OF STUDYING GENETIC CONTRIBUTIONS TO DEVELOPMENT
Behavior Genetics: Adoption and Twin Studies
Shared and Nonshared Environments
Learning from Living Leaders: Sir Michael Rutter
Molecular Genetics: The Human Genome Project
Learning from Living Leaders: Avshalom Caspi
MODELS OF GENETIC INFLUENCE
The Transmission of Traits: A Basic Model
Interactions among Genes
Environment Influences Gene Expression
Genetic Makeup Helps Shape the Environment
Gene–Environment Interactions (G  E)
Gene–Environment Feedback Loops
Research up Close: A Genetic Risk for Drug Use
GENETIC ANOMALIES
Insights from Extremes: Autism
Real-World Application: Genetic Counseling, Genetic Selection
TEMPERAMENT: CAUSES AND CONSEQUENCES
DEFINING AND MEASURING TEMPERAMENT
Cultural Context: Are Temperaments the Same Around the World?
THE BIOLOGICAL BASIS OF TEMPERAMENT
Genetic Factors
Neurological Correlates
EARLY EVIDENCE OF TEMPERAMENT
Learning from Living Leaders: Mary K. Rothbart
CONSEQUENCES AND CORRELATES OF TEMPERAMENT
Into Adulthood: Shy Children Thirty Years Later
<SUM>CHAPTER SUMMARY<SUM/>
KEY TERMS
At the Movies
Learning Objectives
1. Describe what is meant by biological preparedness. Provide research examples illustrating
this concept. Explain how this preparedness is adaptive.
2. Identify and define the different areas of the brain at both the structural and cellular levels
(cerebrum, cerebral cortex and its different regions, corpus callosum, neuron, glial cell,
synapse).
3. Describe the developmental sequence of brain development and how the sequence is linked
to advancements in various areas of functioning.
4. Explain what is meant by hemispheric specialization and lateralization. Describe what
abilities are located in each hemisphere.
5. Describe the processes of neuron proliferation, neural migration, neuronal death,
synaptogenesis, and synaptic pruning. Explain the importance of environmental input in
these processes.
6. Define experience-expectant and experience-dependent processes. Provide examples.
7. Define what a mirror neuron is and what its links are to social behavior.
8. Define what a gene is.
9. Describe the study of human behavior genetics and the heritability factor.
10. Describe the difference between genotype and phenotype.
11. Define what monozygotic and dizygotic twins are and how they are used in the study of
human behavior genetics.
12. Explain the difference between shared and nonshared environments.
13. Describe the basic model of genetic transmission including the definitions of alleles,
homozygous, heterozygous.
14. Describe the notion of interacting genes and specifically modifier genes.
15. Describe reaction range as a form of gene by environment interaction
16. Describe how genes and environments work together via passive, evocative, and active geneenvironment associations.
17. Describe gene  environment interaction models and gene-environment feedback loops.
18. Discuss various genetic anomalies (e.g., Turner syndrome, fragile X syndrome, Williams
syndrome, ADHD, autism).
19. Define temperament. Describe the different types of temperament identified in the research
by Thomas and Chess.
20. Describe Rothbart’s 3 temperament dimensions (effortful control, negative affectivity,
extraversion-surgency).
21. Describe what is known about the biological bases of temperament (genetic factors, neural
correlates, early evidence of temperament).
22. Discuss the correlates and consequences of temperament for children’s social development.
Student Handout 3-1
Chapter Summary
Biological Preparedness
 Babies are biologically prepared for social interactions at birth because of their biological
rhythms and their abilities to regulate them. Infants with better regulation of biological
rhythms have more synchronous social interactions with their mothers.
 Newborns are attracted to the properties of human faces—boundaries, hairlines, chins—as
well as the movement of faces. By 3 months, infants identify faces as unique patterns. The
brain has specialized cells devoted to recognition of faces.
 At birth, babies are attracted to high-pitched sounds, which parents typically use when they
talk to them.
 Newborns can distinguish their mother’s smell from that of other women. They can also
discriminate different tastes and come to prefer tastes they were exposed to during
breastfeeding.
 Newborns are responsive to and soothed by touch.
 Babies are attracted by their mothers’ responsiveness and expressiveness in face-to-face play.
 They interact in synchrony by 3 months.
 Preparedness for social interaction has an evolutionary basis; it is adaptive and ensures the
survival of the infant.
The Neurological Basis of Social Development
 The cerebral cortex is divided into regions in which cells control specific functions, such as
speech, motor abilities, and memory. The cortex and the limbic system play major roles in
regulating emotion and social behavior.
 There is an orderly sequence to brain development during infancy with both gradual
continuous changes and periods of relatively rapid development. Changes are linked to
advances in auditory, visual, motor, and socioemotional development.
 In the 5- to 7-year period, development of the prefrontal cortex is associated with the
development of executive processes such as attention, inhibitory control, and planning.
 Maturation of the cortex continues into adolescence.
 The right cerebral hemisphere controls the left side of the body and is involved in processing
visual-spatial information, face recognition, and emotional expressions. The left hemisphere
controls the right side of the body and is important for understanding and using language.
Hemispheric specialization and lateralization are evident early in infancy and are well
developed by age 3.
 Although most of the brain’s neurons are present at birth, changes take place in their size,
number of connections, or synapses, and production of the surrounding, supportive glial cells.
Myelination increases the speed, efficiency, and complexity of transmissions between
neurons.
 Neural migration distributes neurons throughout brain regions. The abundance of neurons
and synapses is trimmed over time through neuronal death and synaptic pruning.
 The environment plays a critical role in brain development. Enriched environments are
related to increases in brain size, connections among neurons, and activities of key brain

chemicals. Additional experience can also help reduce damage or defects in one area or
hemisphere of the brain.
Two types of processes influence the development of the child’s brain. Experience-expectant
processes are universal, that is, shared by all human beings across evolution. Experiencedependent processes are related to experiences in a particular family or culture.
Genetics and Social Development
 Genetic transmission is another important biological foundation for social development and
accounts for individual differences between people, such as the outgoing and sociable
tendencies versus introversion and shyness.
 Genetic transmission starts with chromosomes, on which are genes—portions of the DNA
molecule containing the genetic code.
 Genetic variability is the result of the huge number of possible chromosome combinations,
crossing over during cell division in the fertilized egg, and sexual reproduction as 23
chromosomes from a woman unite with 23 chromosomes from a man.
 The genotype is the particular set of genes that a person inherits. It interacts with the
environment to produce the phenotype, which is the observable expression of physical and
behavioral characteristics.
 The method that behavior geneticists use most often to investigate the contributions of
heredity and environment to individual differences is the study of family members whose
degrees of biological relatedness are known.
 Children raised in the same family have both shared and nonshared environments.
 The simplest model of genetic transmission applies to characteristics determined by single
genes. A more complex model is based on the interaction of multiple genes. Most
characteristics of social development involve multiple genes acting together. A third model
stresses the interplay between genes and environment.
 Environments influence genes, and genes influence environments. In a passive geneenvironment association, parents create an environment that suits their genetic
predispositions and may also encourage these inherited predispositions in their children. In
an evocative gene-environment association, people’s inherited tendencies evoke certain
responses from others. In an active gene-environment association, each person’s genetic
makeup encourages him or her to seek out experiences compatible with inherited tendencies
(also known as niche picking).
 In the gene × environment (G × E) model of genetic transmission, an active role is given to
both genes and environment, and their contributions are taken beyond additive influences.
Temperament: Causes and Consequences
 Temperament is defined as an individual’s typical mode of responding to the environment.
Temperamental characteristics appear in early infancy.
 Three common temperament dimensions are effortful control, negative affectivity, and
extraversion.
 Heredity contributes to differences in temperament, especially differences in emotionality,
activity level, and sociability.
 Temperament has neurological and neurochemical underpinnings.
 Children with less optimal temperament profiles experience a higher rate of problems in later
life.

To some extent, the likelihood of problems depends on the environment in which the child is
reared and how well it suits the child’s temperamental qualities.
Student Handout 3-2
Key Terms
GLOSSARY TERMS
active gene-environment association
People’s genes encourage them to seek out
experiences compatible with their inherited
tendencies.
allele
An alternate form of a gene; typically, a gene
has two alleles, one inherited from the
individual’s mother and one from the father.
attention deficit/hyperactivity disorder
(ADHD)
A disorder characterized by a persistent pattern
of inattention and hyperactivity or impulsivity.
autism
Disorder that begins in childhood, lasts a
lifetime and disrupts social and communication
skills.
cerebral hemispheres
The two halves of the brain’s cerebrum, left
and right.
cerebral cortex
The covering layer of the cerebrum, which
contains the cells that control specific functions
such as seeing, hearing, moving, and thinking.
cerebrum
The two connected hemispheres of the brain.
corpus callosum
The band of nerve fibers that connects the two
hemispheres of the brain.
dizygotic
Fraternal twins from two different eggs
fertilized by two different sperm, producing
two different zygotes.
evocative gene-environment association
People’s inherited tendencies evoke certain
environmental responses.
experience-dependent processes
Brain processes that are unique to the
individual and responsive to particular cultural,
community, and family experiences.
experience-expectant processes
Brain processes that are universal, experienced
by all human beings across evolution.
externalizing
A type of childhood behavior problem in
which the behavior is directed at others,
including hitting, stealing, vandalizing, and
lying.
gene
A portion of DNA located at a particular site
on a chromosome and coding for the
production of a specific type of protein.
gene-environment interaction (G  E) model
People in the same environment are affected
differently depending on their genetic makeup.
genotype
The particular set of genes a person inherits
from his or her parents.
glial cell
A cell that supports, protects, and repairs
neurons.
heritability factor
A statistical estimate of the contribution
heredity makes to a particular trait or ability.
heterozygous
Alleles for a particular trait from each parent
are different.
homozygous
Alleles for a particular trait from each parent
are the same.
human behavior genetics
The study of the relative influences of heredity
and environment on the evolution of individual
differences in traits and abilities.
internalizing
A type of childhood behavior problem in
which the behavior is directed at the self rather
than others, including fear, anxiety, depression,
loneliness, and withdrawal.
lateralization
The process by which each half of the brain
becomes specialized for certain functions—for
example, the control of speech and language by
the left hemisphere and of visual-spatial
processing by the right.
mirror neuron
A nerve cell that fires both when a person acts
and when a person observes the same action
performed by someone else, as if the observer
himself or herself were acting.
modifier genes
Genes that exert their influence indirectly by
affecting the expression of other genes.
monozygotic
Identical twins created when a single zygote
splits in half and each half becomes a distinct
embryo with exactly the same genes; both
embryos come from one zygote.
myelination
The process by which glial cells encase
neurons in sheaths of the fatty substance
myelin.
neural migration
The movement of neurons within the brain that
ensures that all brain areas have a sufficient
number of neural connections.
neuron proliferation
The rapid formation of neurons in the
developing organism’s brain.
neuron
A cell in the body’s nervous system, consisting
of a cell body, a long projection called an axon,
and several shorter projections called
dendrites; neurons send and receive neural
impulses, or messages, throughout the brain
and nervous system.
niche picking
Seeking out or creating environments
compatible with one’s genetically based
predispositions.
nonshared environment
A set of conditions or activities experienced by
one child in a family but not shared with
another child in the same family.
passive gene-environment association
The environment created by parents with
particular genetic characteristics encourages
the expression of these tendencies in their
children.
phenotype
The visible expression of the person’s
particular physical and behavioral
characteristics; created by the interaction of a
person’s genotype with the environment.
programmed neuronal death
The naturally occurring death of immature
nerve cells during early development of the
nervous system.
reaction range
The range of possible developmental outcomes
established by a person’s genotype in reaction
to the environment in which development takes
place.
shared environment
A set of conditions or activities experienced by
children raised in the same family.
synapse
A specialized site of intercellular
communication that exchanges information
between nerve cells, usually by means of a
chemical neurotransmitter.
synaptic pruning
The brain’s disposal of the axons and dendrites
of a neuron that is not often stimulated.
synaptogenesis
The forming of synapses.
temperament
An individual’s typical mode of response
including activity level, emotional intensity,
and attention span; used particularly to
describe infants’ and children’s behavior.
OTHER IMPORTANT TERMS IN THIS CHAPTER
adoption design
amygdala
auditory preparedness
baby talk
biological preparedness
biological rhythms
canalization
cortex
difficult, easy, and slow-to-warm-up
effortful control
extraversion-surgency
face-to-face interaction
fragile x
genetic feedback loops
goodness of fit
growth spurts
Human Genome Project
molecular genetics
regulatory affect
social brain
social rhythms
temperament x environment interaction
turn taking
Turner syndrome
twin study design
visual preparedness
Williams syndrome
Student Handout 3-3
The Interaction of Heredity and Environment
Answer the following questions about the ways in which genotypes and phenotypes have influenced your decisions.
1.
Give an example from your own life of a way in which a physical genotype has influenced
your decisions (e.g., a tall male decides to pursue basketball rather than gymnastics).
2.
How did the environment hinder or help in this decision? (Think of people, events, and
activities that might have played a role).
3.
Give an example from your own life of a way in which a temperamental genotype has
influenced your decisions (e.g., a shy female decides to spend time on computers rather
than on cheerleading).
4.
How did the environment hinder or help in this decision?
Practice Exam Questions
MULTIPLE CHOICE QUESTIONS
1. People’s genes encourage them to seek out experiences compatible with their inherited
tendencies. This is called: (a) passive gene-environment association (b) *active geneenvironment association (c) evocative gene-environment association (d) genotype
2. An alternate form of a gene is called: (a) a neuron (b) monozygotic (c) *an allele (d) a
heritability factor
3. Which of the following exemplifies an evocative gene-environment association? (a) unhappy
and irritable parents are more likely to provide a negative home environment, which
encourages their children to become antisocial or depressed (b) *parents’ physical punishment
is strongly influenced by the child’s genetic tendency to be antisocial and defiant (c)
individuals who are aggressive sign up for martial arts classes instead of chess club (d) none of
the above
4. The particular set of genes a person inherits from his or her parents is the: (a) *genotype (b)
heritability factor (c) temperament (d) phenotype
5. A nerve cell that fires both when a person acts and when a person observes the same action
performed by someone else, as if the observer himself or herself were acting: (a) glial cell (b)
*mirror neuron (c) modifier gene (d) none of the above
6. A set of conditions or activities experienced by one child in a family but not another child in
the same family comprises: (a) *the nonshared environment (b) the shared environment (c)
niche picking (d) experience-dependent processes
7. The possible developmental outcomes established by a person’s genotype in the environment in
which development takes place is referred to as: (a) niche picking (b) gene-environment
interaction (c) active gene-environment association (d) *reaction range
8. An individual’s typical mode of response, including activity level, emotional intensity, and
attention span, is referred to as: (a) heritability factor (b) *temperament (c) externalizing
problems (d) attention deficit/hyperactivity disorder
9. Babies are biologically prepared for social interactions by: (a) having biological rhythms,
which they soon learn to control and regulate (b) preferring to look at all the visual features that
compose human faces (i.e., large visible elements, movement, clear contours, contrast) (c)
preferring voices over other sounds (d) *all of the above
10. The social brain includes: (a) the hippocampus (b) the cerebellum (c) *the amygdala (d) glial
cells
ESSAY QUESTIONS
1. Describe three developmental consequences of differences in infant temperament.
2. What is a “G x E model” and give an example.
3. Discuss the ways that infants are biologically prepared for social interaction and why this is
theoretically important.