Human Development 1
Chapter 4: Infancy
Growth and Change in Infancy
Changes in Height and Weight
Babies grow at a faster rate in their first year than at any later time of life.
Birth weight doubles by the time the infant is 5 months old, and triples by the
end of the first year, to about 10 kilos on average.
At 6 months, a well-nourished baby looks on the plump side, but by year 1,
the child lose much of their baby fat, and the trend toward a lower ratio of fat
to body weight continues until puberty.
Growth in height in the first year is uneven, occurring in spurts rather than
Cephalocaudal principle: principle of biological development that growth
tends to begin at the top, with the head, and then proceeds downward to the
rest of the body.
Proximodistal principle: principle of biological development that growth
proceeds from the middle of the body outward.
Teeth and Teething.
Teething: period of discomfort and pain experienced by infants as their new
teeth break through their gums
There are several signs that a baby has begun teething, even if a tooth has not
yet broken through.
Parents might notice more drooling, more coughing, and perhaps a rash
around the mouth. Babies also often seize the opportunity for something to
bite when teething.
They also tend to become irritable.
Some may be reluctant to breast or bottle feed because the suction created
from feeding adds to their discomfort.
Neurotransmitter: chemical that enables neurons to communicate across
Axon: part of a neuron that transmits electric impulses and releases
Dendrites: part of the neuron that receives neurotransmitters.
The number of neurons in the brain drops by age 2 to about one-half what it
was at birth.
Overproduction/exuberance: burst in the production of dendritic
connections between neurons.
At birth the neurons have few interconnections, but by age 2 each neuron is
connected to hundreds or even thousands of other cells.
Myelination: process of growth od the myelin sheath around the axon of a
neuron. Myelination is active in the early years of life but continues at a
slower rate until about age 30. Synaptic pruning: Process in brain development in which dendritic
connections that are used become str9onger and faster and those that are
unused whither away.
The brain is divided into 2 major regions: the hindbrain, midbrain, and
The hindbrain and midbrain mature earliest and perform the basic biological
functions necessary to life.
The forebrain is divided into 2 main parts, the limbic system and the cerebral
The structures of the limbic system include the hypothalamus, the thalamus
and the hippocampus.
The hypothalamus plays a role in monitoring and regulating our basic animal
functions, including thirst, hunger, body temperature, sexual desire, and
The Thalamus acts as a receiving and transfer center for sensory information
from the body to the rest of the brain.
The hippocampus is crucial to memory.
Cerebral cortex: outer portion of the brain, containing four regions with
Lateralization: specialization of functions in the 2 hemispheres of the brain
The plasticity of the Infant Brain
Plasticity degree to which development can be influenced by environmental
High plasticity of the Infant brain makes it adaptable but also vulnerable
Two important issues of sleep infancy are the risk of dying during sleep and
the issue of whom infants should sleep with. For both issues, there are
important cultural variations.
Sudden Infant Death Syndrome (SIDS)
Sudden infant death syndrome (SIDS): death within the first year of life
due to unknown reasons, with no apparent illness or disorder
Although deaths from SIDS have no clear cause, there are several factors
known to put infants at risk including:
o Sleeping stomach down instead of flat on the back
o Low birth weight and low Apgar scores
o Having a mother who smoked during pregnancy, or being around
smoke during infancy
o Soft bedding, sleeping in an overheated room, or wearing two or more
layers of clothing during sleep. Human Development 3
Chapter 4: Infancy
Our theory is that babies’ vulnerability to SIDS at 2-4 months old reflects the
transition from reflex behaviour to international behaviour.
One thing that is certain is that sleeping on the back instead of the stomach
makes an enormous difference in lowering the risk of SIDS
Cosleeping: Who sleeps with whom?
Cosleeping: cultural practice in which infants and sometimes older children
sleep with one or both parents.
Custom complex: distinctive cultural pattern of behaviour that reflects
underlying cultural beliefs.
Parents in an individualistic culture may fear that cosleeping will make
infants and children too dependent.
However, children who cosleep with their parents in infancy are actually
SIDS is almost unknown in cultures where cosleeping is the norm. In the
United States, where most parents do not cosleep, rates of SIDS are amoung
the highest in the world.
There appears to be some reasons for this pattern
o Most parents and infants in cosleeping cultures sleep on relatively
hard surfaces such as a mat, on the floor, or a futon, thus avoiding the
soft bedding that is sometimes implicated in SIDS.
o Infants who cosleep breast-feed more often and longer than infants
who do not, and these frequent episodes of arousal in the course of
the night make SIDS less likely
o Cosleeping mothers tend to lay their infants on their backs to make
the mother’s breast more easily accessible for breast feeding.
Introduction of solid foods.
Cultures vary widely in when they introduce solid foods to infants, ranging
from those that introduce it after just a few weeks of life to those that wait
until the second half of the first year.
At 4-5 months, infants still have a gag reflex that causes them to spit out any
solid item that enters their mouths.
In the West, paediatricians generally recommend introducing solid food
during the fifth or sixth month of life.
Malnutrition in Infancy.
Malnutrition in infancy is usually due to the mother is so ill or malnourished
herself that she is unable to produce an adequate supply of breast milk. OR,
she may have a disease that can be communicated through breast milk, such
as tuberculosis or HIV, and she has been advised not to breast-feed.
Marasmus: disease in which the body wastes away from lack of nutrients. Infant Mortality
Causes and prevention of infant mortality
It takes place during the first month of life and is usually due to sever birth
defects or low birth weight, or is an indirect consequence of the death of the
mother during childbirth.
Diseases are another major cause of infant mortality worldwide.
The number one source of infant mortality beyond the first month but within
the first year is diarrhea
Oral rehydration therapy (ORT): treatment for infant diarrhea that
involves drinking a solution of salt and glucose mixed with clean water.
Although millions of infants wordwide die yearly from lack of adequate
mutation and medical care, in the past half century many diseases that
formerly killed infants and young children have been reduced or even
eliminated due to vaccines that provide immuniation.
Typically, children receive vaccinations for these diseases in the first or
second year of life. However, there is a great deal of variability worldwide in
how likely children are to be vaccinated.
Although rumours have circulated that some vaccinations may actually cause
harm to children, for example by triggering autism, scientific studies have
found no basis for these claims.
Cultural Beliefs and Practices to Protect Infants
Historically, parents had no immunizations or other medical care for their
infants, but they often went to great lengths to try and protect their babies
Although they knew nothing about the physiological causes of illness and had
no effective medical remedies, they attempted to devise practices that would
allow their infants to avoid harm.
Today, in cultures where medical remedies for infant illness are scarce,
parents often resort to magical practices intended to protect their babies
from disease and death
The Fulani people of West Africa believe that a sharp knife should always be
kept near the baby to ward off the witches and evil spirits that may try to
take its soul.
Finally, the Ifalaluk of Micronesia believe that neonates should be covered
with cloths in the weeks after birth to encourage sweating which they believe
helps babies grow properly.
Baby on the Move: Motor and Sensory Development.
Gross motor development: Development of motor abilities including
balance and posture as well as whole-body movements such as crawling. Human Development 5
Chapter 4: Infancy
Fine motor development: development of motor abilities involving finely
tuned movements of the hands such as grasping and manipulated
Gross Motor Development
Milestones of Gross Motor Development in Infancy
Milestone Average age Age range*
Holding head up 6 weeks 3 weeks-4 months
Rolling over 4 ½ months 2-7 months
Sitting without support 7 months 5-9months
Crawling 7 months 5-11 months
Standing 11 months 5-12 months
Walking with support 11 ½ months 7-12 months
Walking 12 months 9-17 months
How much infants’ gross motor development is ontogenetic—meaning that it
takes place due to an inborn, genetically based, individual timetable—and
how much of it is due to the experience of learning? As with most aspects of
development, both genetics and environment are involved.
Most developmental psychologists view gross motor development in infancy
as a combination of the genetic timetable, the maturation of the brain,
support and assistance from adults for developing the skill, and the child’s
own efforts to practice the skill.
Looking at infant gross motor development across cultures provides a vivid
picture of how genetic and environments interact.
Even after they learn to crawl at about 6 months old and walk at about one
year old, infants in traditional cultures are restricted in their exercise of
these new motor skills.
Some cultures actively promot infants’ grow motor development.
Infants in cultures where they are strapped to the mother’s back or swaddled
learn to crawl and walk at about the same ages as infants in cultures that
neither bind their infants nor make special efforts to support gross motor
Infants in cultures where gross motor development is actively stimulated
may develop slightly earlier than in cultures where parents make no special
Fine Motor Development
Opposable thumb: position of the thumb apart from the fingers, unique to
humans, that makes possible fine motor movements. The principal milestones of fine motor development in fancy are reaching
and grasping. Oddly, infants are better at reaching during the first month of
life than they are at 2 months of age.
Neonates will extend their arms awkwardly toward an interesting object, an
action called prereaching, although it is more like a swipe or a swing than a
At about 3 months, reaching reappears, but in a more coordinated and
accurate wat than in the neonate.
Grasping is also a neonatal reflex and this means it is not under intentional
control. Like reaching, grasping becomes smoother and more accurate furing
the first year, as infants learn to adjust the positions of their fingers and
thumbs even before their hand reaches the object, and to adjust further once
they grasp the object, in response to its size, shape and weight.
At the same time as infants’ abilities for reaching and grasping are advancing,
they are learning to coordinate the two.
Learning to coordinate reaching and grasping is the basis of further
development of fine motor skills, and an essential part of human motor
By 9-12 months, infants learn the “pincer grasp” that allows them to hold a
small object between their thumb and forefinger.
Depth perception: ability to discern the relative distance of objects in the
Binocular vision: Ability to discern the relative distance of objects in the
Depth perception becomes especially important once babies become mobile.
This was the first demonstrated in a classis experiment by Eleanor Gibson
and James Walk.
o They made a glass covered table with a checkered pattern was just
below the surface whereas on the other half of it was about two feet
below, giving the appearance of a visual cliff in the middle of the table.
o The infants in the study were happy to crawl around on the shallow
side of the cliff, but most would not cross over to the deep side, even
when their mothers stood on the other side of it and beckoned them
encouragingly. This showed that they have learned death perception.
Intermodal perception: integration and coordination of information from
the various senses.
Even neonates possess a rudimentary form of this ability. When we hear a
sound they look in the direction it came from, indicating coordination of
auditory and visual responses.
The early development of intermodal perception helps infants learn about
their physical and social world. Human Development 7
Chapter 4: Infancy
SECTION 2: Cognitive Development
Piaget’s Theory of Cognitive Development.
Mental structure: in Piaget’s theory of cognitive development, the cognitive
systems that organize thinking into coherent patterns so that all thinking
takes place on the same level of cognitive functioning.
Cognitive-developmental approach: Focus on how cognitive abilities
change with age in stage sequence of development, pioneered by Piaget and
since taken up by other researchers.
What Drives Cognitive Development?
Maturation: concept that an innate, biologically based program is the
driving force behind development.
Along with maturation, Piaget emphasized that cognitive development is
driven by the child’s efforts to understand and influence the surrounding
Schemes: Cognitive structures for processing, organizing, and interpreting
The two processes involved in the use of schemes are assimilation and
Assimilation: altering new information to fit an existing scheme
Accomodation: changing a scheme to adapt to new information.
Ages Stage Characteristics
0-2 Sensorimotor Capable of coordinating the
activities of the senses with
2-7 Preoperational Capable of symbolic
representation, such as in
language, but with limited
ability to use mental
7-11 Concrete operational Capable of using mental
operations, but only in
11-15 and up Formal Operations Capable of thinking logically
and abstractly; capable of
formulating hypotheses and
testing them systematically;
thinking is more complex;
and can think about