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CHAPTER FOUR SUMMARY
During the first 2 years, body size increases dramatically—faster than at any other time after birth. Body
fat is laid down quickly in the first 9 months, whereas muscle development is slow and gradual. Children
of the same age differ in rate of physical growth; some make faster progress toward a mature body size
than others. The best way to estimate a child’s physical maturity is by using skeletal age. Early in
development, the brain grows faster than any other organ of the body. As neurons form an elaborate
communication system in the brain, stimulation becomes necessary for their survival. The cerebral
cortex is the largest, most complex brain structure—accounting for 85 percent of the brain’s weight,
containing the greatest number of neurons and synapses. Its frontal lobes, which contain the prefrontal
cortex, have the most extended period of development. At birth, the two hemispheres of the cerebral
cortex have already begun to specialize, a process called lateralization. However, the brain is more
plastic during the first few years than it will ever be again. Animal research and natural experiments with
children who were victims of early, prolonged institutionalization provide evidence for sensitive periods
in brain development. Appropriate stimulation is vital for experience-expectant brain growth—the
young brain’s rapidly developing organization, which depends on ordinary experiences. Experiencedependent brain growth, in contrast, occurs throughout our lives as a result of specific learning
experiences. Physical growth, like other aspects of development, results from a complex interplay
between genetic and environmental factors. Heredity, nutrition, and emotional well-being all affect
early physical growth. Dietary diseases caused by malnutrition affect many children in developing
countries. If allowed to continue, body growth and brain development can be permanently stunted.
Breastfeeding provides many benefits to infants, especially to those in poverty-stricken areas, where it
protects against disease and prevents malnutrition and infant death. Babies come into the world with
built-in learning capacities that permit them to profit from experience immediately. Classical and
operant conditioning, habituation and recovery, and imitation are important avenues through which
infants learn about their physical and social worlds. Babies’ motor achievements have a powerful effect
on their social relationships. According to dynamic systems theory of motor development, each new
motor skill is a joint product of central nervous system development, the body’s movement capacities,
the child’s goals, and environmental supports for the skill. Cultural differences in infant-rearing practices
affect the timing of motor development. Perception changes remarkably over the first year of life.
Hearing and vision undergo major advances during the first 2 years as infants organize stimuli into
complex patterns, improve in perception of depth, and combine information across sensory modalities.
According to Eleanor and James Gibson’s differentiation theory, perceptual development is a matter of
detecting invariant features in a constantly changing perceptual world, and seeking ways in which the
environment affords possibilities for action.
Instructor’s Resource Manual for Berk / Development Through the Lifespan, 6e Copyright © 2014,
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