How Children Develop
Siegler, R., Saffran, J., Eisenberg, N., DeLoache, J., & Gershoff, E. (2017). How
Children Develop (5th edition). New York: Worth Publishers.
Chapter 3 (pp. 92-126): Nature and Nurture, Behavior Genetics &
Brain Development
Nature and Nurture
19th Century:
• Galton (Darwin’s cousin) Certain traits (e.g., eminence, and talent) run in families
• Mill: Environmental factors (e.g., economic well-being) play a stronger role than
hereditary ones.
• Mendel: observed different patterns of inheritance in plants
20th century:
• Watson, Crick &Franklin: Identification of DNA structure.
21st Century:
• Gene sequencing: genome of approximately 250 animals mapped
Genome complete set of an organism’s genes.
• Gene synthesis: a method for producing DNA biological parents unnecessary.
In 2016 human genome project (synthesize the entire human genome)
unethical.
• Humans have approximately 19,000 genes, most overlap with other species.
Development= experience + genes
GENETICS AND ENVIRONMENTAL FORCES
Child development involves:
Genotype: Genetic material inherited from parents
Phenotype: Observable genotype expression (physical
characteristics and behavior)
Environment: Every aspect of a child’s surroundings (including prenatal experience) other
than genes themselves
These 3 elements are involved in 5 relations that are fundamental in development:
Model of hereditary and environmental influences:
,1. Parent’s genotype-child’s genotype (The parent’s genetic contribution to the child’s
genotype).
Genotype parents Genotype child
Transmission of genetic material from parents to offspring: two gametes (one from the
mother and one from the father) conjoin in conception to form zygote.
Thus Every individual has two copies of each gene one from the chromosome
inherited from the mother and one from the father.
Every cell nucleus in the body contains chromosomes, which are made up of DNA
(deoxyribonucleic acid); genes (basic units of heredity) are parts of the DNA.
Each gene segment of DNA that is the code for a particular protein regulate cell
functioning. Genes affect behavior through manufacture of proteins.
genes make up only the 2% of human genome Thus, noncoding DNA vital to
functioning.
Human Heredity and Sex determination:
Human cell nuclei usually contain 46 chromosomes, divided into 23 pairs in the nucleus of
each cell.
Sex chromosomes determine an individual’s gender:
Females: XX & Males: XY
Father determines offspring’s gender: All eggs have an X chromosome, whereas sperm have
either an X or Y (much smaller) chromosome.
Genetic Diversity:
Genes guarantee that humans will be similar to one another in certain ways (as a species
and within families), but genes also guarantee individual differences.
, • Mechanisms that contribute to genetic diversity among people:
1. Mutation a change in a section of DNA.
➢ Causes:
▪ Random, spontaneous errors
▪ Environmental factors
➢ Consequences:
▪ Increased survival (through better environmental adaptation or resistance
to disease)
▪ Harmful effects: Many inherited diseases and disorders originate from a
mutated gene.
2. Random assortment of chromosomes in the formation of eggs and sperm:
occurs during meiosis (gamete division): 23 pairs of chromosomes are shuffled
randomly and each member of each pair go into a new egg or sperm at random
8.4 million possible combinations of chromosomes
when sperm & egg unite, odds are essentially zero that two individuals (even
family members) have same genotype (except identical twins)
3. Crossing over = the process by which sections of DNA switch from one
chromosome to the other
➢ Consequence: Some of the chromosomes passed on by parents to their
offspring are different from their own
GENETIC TRANSMISSION DISORDERS:
Dominant-Recessive (or Mendelian) Patterns
Many genetic disorders involve the dominant-recessive patterns of inheritance
▪ Recessive gene disorder occurs when an individual has two recessive alleles for
the condition. E.g. PKU, Sickle-cell anemia, etc.
▪ Dominant genes disorders e.g. Huntington disease (progressive and fatal
degenerative condition of the brain; Neurofibromatosis (nerve fibbers develop
tumors)
, ✓ In some cases, a single gene can have harmful and beneficial effects e.g.
sickle cell disease (red blood cells are sickle shaped rather than round
diminishing capacity to transport oxygen)
The benefit of this gene sickle cell genes confer resistance again the malaria
deadly disease.
❖ Individuals who are homozygotes of this trait inherit two sickle cell
gene
❖ Individuals who are heterozygotes of this gene carry one normal and
one sickle cell gene, usually don’t experience the negative effects.
*Note even when the root cause of a disorder is a single gene, it doesn’t mean that that
one gene is responsible for all manifestations of the disorder.
Polygenic Inheritance Disorders that result from interactions among multiple genes and
environmental factors e.g. asthma, and psychiatric disorders such as schizophrenia, etc.
GWAS suggests that each gene has a small effect on its own the combination with the
other genes and environment is what leads to disorders.
*Behaviors and dispositions involve polygenic Inheritance!
Sex-Linked Inheritance:
Some single-gene conditions are carried on the X chromosome much common in males
(females inherit it if they inherit the culprit recessive alleles on both of their X
chromosomes) e.g male pattern baldness, red-green colour blindness, haemophilia and
Duchenne muscular dystrophy.
Chromosomal Anomalies genetic disorders due to extra or missing sex chromosomes.
E.g:
▪ Down Syndrome mother’s eggs do not divide properly and the egg that its
fertilized contains one extra copy of the chromosome 21 women older than 35,
higher risk. (increased paternal age also higher risk, but to a lesser extent).
▪ Klinefelter syndrome affects males involves an extra X chromosome (XXY)
small testes, elongated limbs and infertility.
▪ Turner Syndrome affect women missing X chromosome (X0) Characteristics:
short stature, infertility and stunted sexual development.
Gene Anomalies
Genetic disorders due to extra, missing or abnormal gene.
E.g:
▪ Williams syndrome 21 genes on chromosome 7 cognitive impairments
Regulator-Gene Defects:
Regulator genes control the expression of other genes. Defects in regulator genes can cause
disorders.
, ▪ E.g. Defect in the regulator gene that initials the development of a male can
result in a new-born who has a female genitalia but that is genetically male.
Unidentified Genetic Basis
▪ E.g. Dyslexia highly heritable reading disability, but inheritance patterns not yet
identified.
▪ Tourette syndrome: involuntary twitching.
▪ ASD (Autism Spectrum Disorder) = Autism (impairments on social interaction and
communication skills) + Asperger syndrome. more common in boys.
remarkable talents in a specific area.
2. Child’s Genotype-Child’s Phenotype (The contribution of the child’s genotype to
his or her own phenotype)
Endophenotypes: Intermediate phenotypes, including the brain and the nervous system,
that do not involve overt (observable) behavior. Endophenotypes then mediate pathways
between genes and behavior.
Gene activity depends on:
▪ Regulator genes (genes that control the activity of other genes turn on and off)
genes never function in isolation big network of genes.
▪ External factors can also influence the on and off switching of genes e.g. visual
experience to develop a normal visual system.
Only some of the genes you inherit are expressed due to different alleles.
Alleles: Two or more different forms of a gene.
Patterns of expression:
▪ Homozygous: two dominant alleles or two recessive alleles of a certain trait. the
corresponding trait will be expressed, with either two recessive alleles or two
dominant alleles.
▪ Heterozygous: one dominant allele and one recessive allele of a certain trait. the
instructions of the dominant allele will be expressed.
Thus, a dominant allele will override a recessive allele instructions of recessive allele will
only be expressed if homozygous
3. Child’s environment- Child’s Phenotype (The child’s environment to his or her own
genotype)
Norm of reaction = all phenotypes that can theoretically result
from a given genotype in relation to all the environments in
which it can survive and develop.
,Genotype x environmenta given genotype will develop differently in different
environments (i.e., unique phenotypes)
Genotype-environment interactions can be studied by assigning animals with known
genotypes to different environmental conditions ethically, cannot be done with humans
Naturally occurring examples of genotype-environment interactions:
▪ Phenylketonuria (PKU): defective recessive gene on chromosome 12. Individuals
who inherit this gene cannot metabolize phenylalanine (amino acid) thus, if they
eat food with phenylalanine intellectual impairments can result; BUT if its identified
shortly after birth with a diet free of phenylalanine intellectual impairment can be
avoided.
▪ Antisocial Behavior: Suffering abusive treatment and possessing a variant of MAOA
gene (associated with the inhibition of aggression) young men that had an
inactive version of MAO and who experienced maltreatment MORE ANTISOCIAL!
MAOA gene activity moderates relation between childhood maltreatment and
antisocial behavior in early adulthood.
PARENTAL CONTRIBUTIONS
▪ The obvious: Parents contribute to a child’s phenotype through parent-child
interactions and the home environment, experiences, and encouragement they
provide.
▪ The less obvious: parents’ own genetic makeup contributes to the environment they
provide (gene-environment correlations) e.g. a child of a musician is more likely
to grow up listening to music; or parents that like to read more likely to do so with
their children.
Genetic Testing:
▪ Carrier Genetic Testing: genetic test used prior to pregnancy to determine whether
prospective parents are carriers of a specific disorder.
▪ Prenatal Testing: genetic testing during pregnancy used to assess the fetus’s tisk for
genetic disorders.
▪ Newborn Screening: new born infants are screened for both genetic and not-genetic
disorders (e.g. metabolic and endocrine disorders, hearing lose, etc)
4. Child’s Phenotype-Child’s environment (The influence of the child’s phenotype on
his or her environment)
Children actively create their environment:
▪ They elicit different social interactions (temperament)
, ▪ They select different surroundings and experiences (based on their interests, talents,
and personality characteristics)
▪ As children become more autonomous (through self-locomotion) their contributions
to their own environment become more apparent.
5. Child’s Environment-Child’s Genotype (The influence of the child’s environment on
his or her genotype)
Epigenetic mechanisms, mediated by the environment, can alter gene functioning or gene
expression.
▪ Example: Methylation levels depend on experience and thus become increasingly
different between individuals, with age E.g. twins at 3 (no differences in
Methylation) and twins at 50 (completely different methylation levels) the greater
the differences in life time experiences, the greater the differences in methylation
levels.
▪ Low-quality maternal care has epigenetic effect, permanently changing the animal’s
pattern of gene expression poor maternal care affects the methylation of genes
involved in glucocorticoid receptors, which influences stress coping abilities in
offspring.
Behavior Genetics
Behavior genetics The science concerned with how variation in behavior and
development results from gene- environment interactions.
Key ideas:
▪ All behavioral traits are heritable (i.e., influenced by genes to some extent)
▪ Most traits are polygenic (affected by the combination of many genes) and
multifactorial (traits that are affected by a host of environmental and genetic
factors)
Premises:
▪ Genotypically similar individuals should be phenotypically similar (behavior patterns
should “run in families”)
▪ Individuals who were reared together should be more similar than those reared
apart
Behavior Genetics Research designs:
➢ Family study
1. Measurement of trait in people who vary in genetic relatedness
2. Assessment of correlations between measures of trait among those individuals
(parents and children, identical or fraternal twins, etc.)
3. Comparison of correlations as a function of relatedness/environment
- Twin study: compares MZ to DZ twins (equal environments assumption) if there is a
big difference between the correlation of MZ and DZ twins on a specific trait then
important genetic factors are assumed.
,- Adoption study: compares resemblances with biological to resemblances with adoptive
parents and siblings Genetic differences are inferred to the extent that children
resemble their biological relatives more than they do to their adopted ones.
Adoptive-twin study (ideal design!): compares MZ twins who grew up together with MZ
twins who grew up apart
Family Study of Inteligence MZ twins resemble more in IQ than fraternal ones, although,
IQ of MZ twins is not identical thus, environmental factors inferred.
Heritability APPLIES ONLY TO A PARTICULAR POPULATION IN A PARTICULAR
ENVIRONMENT! and it’s the estimated proportion of measured individual variance on a
trait attributed to genetic individual differences.
▪ Heritability estimate says nothing about the relative genetic and environmental
contributions in an individual, rather about the genetic variation in a given
population in a particular environment at a particular time e.g. The heritability
estimate for intelligence is 50% meaning that, for the population studied, roughly
50% of the variation in IQ scores is due to genetic differences among the members of
the population.
▪ High heritability does not imply immutability Genetic change is always possible
through environmental interventions.
Genes code proteins which affect behavior by affecting sensorial, neural and other
physiological processes involved in behavior
New approaches of heritability Genome-wide complex trait Analysis (GCTA) measures
actual genetic similarity consider actual genetic overlap among unrelated people.
ENVIRONMENTAL EFFECTS
▪ Environmental effects can be inferred from heritability estimates (usually >50%)
▪ Shared-environment effects: factors that make siblings more similar (than expected
based on genetic relatedness)
▪ Nonshared-environment effects: factors that are unique to the individual—they
make siblings more different from each other (e.g., peer influences)
Brain development
Neuron: cells that are specialized for sending and receiving messages between the brain
and all parts of the body, and within the brain. constitute the gray matter of the brain
- Sensory neurons transmit info. from sensory receptors from within or outside the
body.
- Motor neurons transmit info. from the brain to the muscles and glands
- Interneurons intermediaries between sensory and motor neurons.
,3 main components of neurons 1. Cell body (biological material that keeps it
functioning); 2. Dendrites ( receive input from other cells and conduct electrical impulses
towards the cell body); 3. Axon ( conducts inputs away from the cell body towards
connections with other neurons).
Neurons communicate via Synapses (microscopic conjunctions between an axon
terminal and the dendrites of another neuron) the chemical messages cross synapses can
either exit or inhibit the postsynaptic neuron.
Glia cells brain cells that provide supportive functions they create the:
▪ myelin sheath increases the speed of info. transmission. If affected, disorders
can be the result:
✓ Multiple sclerosis disease in which immune system attacks myeline
causing physical and cognitive impairments.
✓ People with schizophrenia: show disruption in white matter linked with
genes that regulate myelination.
The cerebral cortex constitutes 80% of the human brain
*Convolutions increase with evolution and during development.
Functional localization:
▪ Cerebral hemispheres sensory input from one side of the body activates the
other side of the brain.
o They communicate through corpus callosum (fibers that connects
them)
o The two hemispheres are specialized for different modes of
processing, this is called cerebral lateralization.
o Left hemisphere specialized in speech and language
▪ Lobes:
o Occipital Processes visual Information
o Temporal Associated with memory, visual recognition, processing
emotions and auditory information
, o Parietal Important for special processing and integrates sensory input
with information stored in memory.
o Frontal Associated with organizing behavior ability to plan.
▪ Association areas process and integrates information from other areas
lies between major sensory and motor areas.
DEVELOPMENTAL PROCESSES
Neurogenesis = proliferation of neurons through cell division
▪ begins 42 days after conception and completed by the midpoint of gestation.
▪ We do continue to generate new neurons throughout life (in rewarding
conditions) neurogenesis occurs in the hippocampus (important for memory)
▪ Can also be inhibited by stress; thus, it’s an adaptive process.
Arborization: increase in size and complexity of dendrites “tree” the most intense period
occurs after birth.
Myelination = formation of myelin (fatty sheath) around axons
✓ increases speed of information processing
✓ begins before birth continues to early adulthood.
✓ White matter (myelinated axons), lie below gray matter (cell bodies in the surface of
cortex)
Mapping the mind
Event related potentials (ERPs)= changes in the brain’s electrical activity that occur in
response to the presentation of a particular stimulus.
MEG Magnetoencephalography non-invasive detects fetal neural responses.
Resting-state functional magnetic resonance imaging (r-s-fMRI) measures brain activity
in the absence of any external stimuli while asleep. reveal early-emerging networks in
infancy.
PET measures brain’s metabolic processes
NIRS (Near-infrared spectroscopy) measures neural activity detects metabolic
changes that lead to different absorption of infrared light in brain tissue. this technique
showed that the auditory cortex of deaf children responded to sound within hours after an
implant, even though the cortex had never before been exposed to sound.
Synaptogenesis = process by which neurons form synapses trillions of connections.
A consecuence of this hyperconnectivity synesthesia –blending of different types of
sensory input-.
Synaptic pruning = elimination of synapses (~40%)
Brain Maturation
Parts associated with basic functions in the cortex mature earlier than areas involved in
higher functions.
