This document summarizes key points from Chapter 3 of the textbook "How Children Develop" regarding the influence of nature and nurture on development. It discusses how both genetic and environmental factors shape individuals' characteristics in complex ways. Specific topics covered include brain development, the interplay between genes and the environment, sensitive periods of development, the importance of experience in shaping the brain, and physical growth patterns in children.

1. Biology and Behavior
How Children Develop (3rd ed.)
Siegler, DeLoache & Eisenberg
Chapter 3

2. Overview
 I. Nature and Nurture
 II. Brain Development
 III. The Body: Physical
Growth and Development

3. I. Nature and Nurture
A. Genetic and Environmental Forces
B. Behavior Genetics

4. A. Nature and Nurture
 Both heredity and
environment influence
individuals’
characteristics.
 When scientists first began
to investigate the
contributions of heredity
and environment, they
generally emphasized one
factor or the other as the
prime influence.
 Recent efforts to map the
human genome
established that individuals
differ from one another by
only about 1 to1.5% of their
genes.

5. 1. Genetic and Environmental Influences
 The interplay between
genes and experience
is very complex.
 This model of
hereditary and
environmental
influences can help to
simplify this interplay.

6. Three Key Elements of the Model
 Genotype: the genetic material an
individual inherits
 Phenotype: the observable expression
of the genotype, including body
characteristics and behavior
 Environment: includes every aspect of
the individual, and his or her
surroundings, other than genes

7. Four Fundamental Relations
1. Parents’ genetic contribution to the
child’s genotype
2. Contributions of the child’s genotype
to his or her own phenotype
3. Contribution of the child’s
environment to his or her own
phenotype
4. Influence of the child’s phenotype on
his or her environment

8. Four Fundamental Relations
Parents’
Genotype
Parents’
Genotype
Child’s
Genotype
Child’s
Genotype
Child’s
Environment
Child’s
Environment
Child’s
Phenotype
Child’s
Phenotype

9. Relation 1: Parents’ and Child’s
Genotypes
 Genetic material is
passed on as
chromosomes—long,
threadlike molecules
made up of DNA
 Carry all the biochemical
instructions involved in the
formation and functioning of
an organism
 Genes are sections of
chromosomes that are the
basic units of heredity for all
living things Karyotype

10. Sex Determination
Sex chromosomes determine an
individual’s sex.
Females have two X chromosomes in the 23rd
pair,
whereas males have an X and a Y chromosome.
A gene on the Y chromosome encodes the
protein that triggers the formation of the testes,
which subsequently produce testosterone, which in turn
takes over the molding of maleness.

11. Diversity and Individuality
 Mutations: changes in sections of DNA caused by
random or environmental factors
 Random assortment: the shuffling of the 23 pairs of
chromosomes in the sperm and egg; chance
determines which member of the pair goes into the
new sperm and egg
 Crossing over: the process by which sections of
DNA switch from one chromosome to another
during meiosis, further increasing genetic variability

12. Relation 2: Child’s Genotype
and Phenotype
 Although every cell
in your body
contains copies of
all the genes you
received from your
parents, only some
of those genes are
expressed.

13. Gene Expression:
Developmental Changes
 Regulator genes largely control the
continuous switching on and off of genes
that underlie development across the
lifespan.
 A given gene influences development and
behavior only when it is turned on.

14. Gene Expression
About a third of human genes have two
or more different forms, known as alleles.
 The dominant allele is the form of the gene
that is expressed if present.
 The recessive allele is not expressed if a
dominant allele is present.
 A person who inherits two of the same alleles
for a trait is described as homozygous.
 A person who inherits two different alleles for a
trait is described as heterozygous.

15. Mendelian Inheritance Patterns

16. Polygenic Inheritance
 When traits are governed by more than
one gene
 Applies to most traits and behaviors of
interest to behavioral scientists

17. Relation 3: Child’s
Environment and Phenotype
 As the model indicates, the child’s
observable characteristics result from the
interaction of environmental factors and
the child’s genetic makeup.

18. Norm of Reaction
Refers to all the
phenotypes that
could theoretically
result from a given
genotype, in
relation to all the
environments in
which it could
survive and
develop

19. PKU
 Children with phenylketonuria (PKU)
—a disorder that is related to a
defective gene on chromosome 12—
are unable to metabolize
phenylalanine.
 With early diagnosis and a properly
restricted diet, however, mental
retardation resulting from PKU can be
avoided.

20. Genetic Transmission of
Diseases and Disorders
 Over 5,000 human diseases and disorders are
presently known to have genetic origins.
 Recessive gene: PKU, sickle-cell anemia, Tay-Sachs
disease, cystic fibrosis
 Single dominant gene: Huntington’s disease,
neurofibromatosis
 Polygenic inheritance: cancer, heart disease, asthma,
psychiatric disorders, behavior disorders

21. Genetic Transmission of
Diseases and Disorders
 Sex-Linked inheritance: male-pattern baldness, red-
green color blindness, hemophilia, Duchenne muscular
distrophy, fragile-X syndrome
 Chromosomal anomalies: Down syndrome (trisomy 21),
Kleinfelter syndrome (XXY), Turner syndrome (XO)

22. Genetic Transmission of
Diseases and Disorders
 Regulator gene defects: genetic male with female
genitalia
 Unidentified genetic basis: autism spectrum disorder
(ASD)

23. The Case of MAOA
 Young men who had
experienced severe
maltreatment were in
general more likely
to engage in
antisocial behavior
than those who had
experienced none.
 However, the effect
was much stronger
for those individuals
who had a relatively
inactive MAOA gene.

24. Parental Contributions to the
Child’s Environment
 A highly salient and
important part of a
child’s environment
is the parents’
relationship with the
child.

25. Relation 4: Child’s Phenotype
and Environment
 Children are active creators of the
environment in which they live.
 By virtue of their nature and behavior, they evoke
certain kinds of responses from others.
 They also actively select surroundings and
experiences that support their interests, talents, and
personality characteristics.

26. B. Behavior Genetics
 The science concerned with how
variation in behavior and
development results from the
combination of genetic and
environmental factors
 Question: Why are people different
from one another?
 Answer: Behavioral traits are
heritable—influenced by hereditary
factors

27. B. Behavior Genetics
 Behavioral geneticists believe that most
traits of interest are multifactorial.
 They are affected by many environmental factors as
well as by many genes.

28. 1. Behavior Genetics Research Designs
 The family study is the mainstay of modern behavior-
genetics research.
 Measure trait of interest among people who vary in
genetic relatedness
 Correlations between the measure of the trait in
individuals with different
relationships are
examined to see if they
are higher for individuals
who:
 Are genetically more
similar
 Share the same
environment

29. Types of Family Studies
 Twin-Study Designs:
Correlations for pairs of
monozygotic twins on a
trait of interest are
compared to those of
dizygotic twins.
 Adoption Studies:
Researchers examine
whether adopted
children are more like
their biological or their
adopted relatives.

30. Family Studies of Intelligence

31. Identical Twins Reared Apart
 Studied twin siblings who have not
met since they were infants
 The team of investigators were struck by
the similarities they found in traits like IQ,
reaction to stress, and traditionalism.
 These similarities may be influenced by
selective placement and similarities in
fostering environments as well as by
genetic factors.

32. 2. Heritability
 A statistical estimate of the proportion of the
measured variance on a given trait among
individuals in a given population that is
attributable to genetic differences among
those individuals.
 Limitations:
 They apply only to populations, not to individuals
 They apply only to a particular group living at a
particular time
 They can differ markedly for groups of people who
grow up in very different environments
 High heritability does not imply immutability
 They say nothing about differences between groups

33. 3. Environmental Effects
 Most obvious source of shared environment is growing up
together in the same family.
 Behavioral geneticists, however, have found surprisingly little
effect of shared environment on some aspects of development.
 Nonshared environment effects include experiences unique
to the individual.
 Siblings may have quite different
experiences within the same family
and their experiences outside the
family may diverge sharply.
 The primary effect of nonshared
environmental factors is to
increase the differences among
family members.

34. II. Brain Development
A. Structures of the Brain
B. Developmental Processes
C. The Importance of Experience
D. Brain Damage and Recovery

35. A. Structures of the Brain
 Neurons are specialized cells that are
the basic units of the brain’s
information system.
 Cell body: contains the basic biological
material that keeps the neuron functioning
 Dendrites: receives input from other cells
and conducts it toward the cell body
 Axon: conducts electrical signals to
connections with other neurons
 These connections are called synapses

36. The Neuron

37. 2. Glial Cells
 Glial cells are the brain’s white matter and
outnumber neurons 10 to 1.
 Cells in the brain that provide a variety of critical
supportive functions
 For example, glial cells form a myelin sheath around certain
axons, providing insulation that increases the speed and
efficiency of information transmission.
 Play a role in communication within the brain.

38. 3. Cerebral Cortex
 Lobes are major areas of the cortex that are
associated with different categories of behavior.
 Occipital lobe: primarily associated with processing visual
information
 Temporal lobe: involved in memory, visual recognition, and the
processing of emotion and auditory information
 Parietal lobe: governs spatial processing and integrates sensory
input with information in memory
 Frontal lobe: organizes behavior and is responsible for planning
 Information from multiple sensory systems is
processed and integrated in the association areas.

39. Cerebral Cortex

40. Cerebral Lateralization
 The cortex is divided into two separate
halves, called cerebral hemispheres,
which communicate through a dense tract
of fibers, the corpus callosum.
 The two hemispheres are specialized for
different modes of processing, a
phenomenon referred to as cerebral
lateralization.

41. B. Developmental Processes
 Question: How does the structure of the
human brain come into being?
 Answer: It is a partnership between
nature and nurture.

42. 1. Neurogenesis and
Neuron Development
 Neurogenesis is the proliferation of neurons
through cell division, is largely complete by
about 18 weeks after conception.
 Neurons migrate to their destinations,
where they grow and differentiate.
 Axons elongate.
 Dendrites form spines that increase their
capacity to form connections with other neurons.
 In the cortex, the most intense period of growth
and differentiation occurs after birth.

43. Myelination
A fatty sheath of myelin that
forms around some axons in
order to speed and increase
information-processing
abilities.

44. Mapping the Mind
 Techniques used to map the mind and its
workings in children:
 Neuropsychological Approach: examining
effects of brain damage on behavior

45. Electrophysiological Recording
 EEG (electroencephalographic)
recordings of electrical activity
generated by active neurons
 ERPs (event-related potentials)
record changes in the brain’s
electrical activity in response
to the presentation of a
particular stimulus.

46. ERP Responses
 These graphs show ERP waveforms in response to novel (red line)
and familiar (yellow line) stimuli.
 The infants who later recalled how to assemble a toy (left panel)
had clearly discriminated between the familiar and novel items on
an earlier recognition test.
 The infants who did not recall the assembly sequence (right panel)
had not discriminated between the components on the earlier test.

47. Brain Imaging Techniques
 fMRI (functional magnetic
resonance imaging) uses a
powerful magnet to produce
colorful images representing
cerebral blood flow in
different areas of the brain.
 PET (positron emission
tomography) uses a
radioactive material injected
into the brain for diagnostic
purposes.

48. 2. Synaptogenesis and Synapse Elimination
 Synaptogenesis
 Each neuron forms synapses with thousands of
other neurons, resulting in the formation of
trillions of connections.
 Synaptic Pruning
 The extensive generation of neurons and
synapses results in an overabundance that
must be eliminated.
 Synaptic pruning occurs at different times in
different areas of the brain and is not fully
completed until adolescence.

49. Synapse Production and Elimination

50. The Adolescent Wave
 Recent research indicates that the
amount of gray matter increases
dramatically in adolescence and
then begins to decline.
 This second wave of synapse production
and pruning may be linked to the
impulsive, irrational behavior, which is
characteristic of adolescence.

51. Brain Maturation
The bluer the image, the more mature that part of the cortex is
(i.e., the gray matter has been replaced with white matter).

52. C. The Importance of Experience
 Plasticity is the capacity of the brain
to be affected by experience.
 Experience plays a central role in
determining which of the brain’s
excess synapses will be pruned and
which will be maintained.
 Synapses that are frequently activated
are preserved, a process described as
“neural Darwinism.”

53. 1. Experience-Expectant Processes
 Experience-expectant plasticity is the
process through which the normal wiring of
the brain occurs in part as a result of the
kinds of general experiences that every
human who inhabits any reasonably normal
environment will have.
 Is accompanied by vulnerability.
 If the expected experience is not available, as in the case
of congenital cataracts, development will be impaired.

54. Sensitive Periods
 A key element in experience- expectant
plasticity is timing.
 There are a few sensitive periods when
the human brain is particularly sensitive
to particular kinds of external stimuli.

55. Experience-Dependent Processes
 Experience-
dependent plasticity
is the process
through which
neural connections
are created and
reorganized
throughout life as a
function of an
individual’s
experience.

56. D. Brain Damage and Recovery
Timing and plasticity play
important roles.
 The worst time to suffer brain damage is
when neurogenesis and neuron migration
are occurring (during prenatal development
and the first year after birth).
 The greatest plasticity is observed when
synapse generation and pruning are
occurring during early childhood.

57. Emergent Effects
of Early Brain Damage
 At 6 years of age, children with congenital brain damage scored
the same as normal children.
 However, the children with brain damage failed to improve and
fell progressively farther behind the normal children, so that by
adolescence there were large differences between the two groups.

58. III. The Body: Physical
Growth and Development
A. Growth and Maturation
B. Nutritional Behavior

59. A. Growth and Maturation
 Compared with most other species, humans
undergo a prolonged period of physical
growth, which occurs during about 20% of
the life span.
 Growth is uneven across age, occurring
most rapidly during the first 2 years of life
and early adolescence.
 Growth is also uneven over different parts
of the body.

60. Growth Curves

61. Variability
 Secular trends are marked changes in physical
development that have occurred over
generations, resulting from environmental
changes such as improvement in health and
nutrition.
 One such change that occurs during puberty, especially
among American girls, relates to how an individual
perceives and feels about her or his physical appearance,
or body image.

62. Failure-to-thrive (FTT)
 A condition in which infants
become malnourished and fail to
grow for no apparent medical
reason.
 It is associated with
disturbances in mother-child
interaction that are thought to
stem from characteristics of
both child and mother.

63. B. Nutritional Behavior
 1. Infant Feeding:
Although breast
milk is nutritionally
superior, the
majority of infants
in the United States
are exclusively or
predominantly
formula-fed.

64. 2. Development of Food Preferences
and Regulation of Eating
 While some food preferences are
innate, experience has a major
influence on children’s food
preferences and consumption
from infancy onwards.
 Children whose parents try to
control their eating habits tend to
be worse at regulating their food
intake themselves than children of
parents who let their children have
more control over their eating.

65. 3. Obesity
 The proportion of U.S. children
who are overweight has
tripled in the past two decades.
 Both genetic and
environmental factors
contribute to this increase.
 Overweight children and teens
suffer a variety of social
problems.

66. Overweight—a growing problem

67. “Fat runs in families”
The overweight children and adults in this painting are all
genetically related, and they are all overeating.

68. 4. Undernutrition
 Forty percent of the world’s children under
age 5 are undernourished.
 Undernutrition and malnutrition are almost
always associated with poverty.
 Malnutrition affects development directly and
indirectly by leading children to withdraw
from their environments to reduce energy
expenditure.

69. Malnutrition and
Cognitive Development