INFANCY AND CHILDHOOD
Nine
months after conception, the human fetus is ready to leave the uterus to enter
the outer world. Ready, however, is a
relative term. Most other animals can walk shortly after birth, and many can
take care of themselves almost immediately. Humans, in contrast, are
extraordinarily helpless at birth and remain utterly dependent on others for
many years.
Why
is human development so slow? Lions (as just one example) chase their male cubs
away from the pride by age 2 or 3. Human parents, in contrast, care for their
offspring for the better part of 2 decades (or more!). One might think that
this would be a great disad-vantage for our species. It turns out, though, that
this long period of dependency is ideal for a creature whose major
specialization is its capacity for learning and whose basic invention is
culture—the ways of coping with the world that each generation hands on to the
next. Human infants, in other words, have a huge capacity for learning and a
great deal to learn. Under these circumstances, there is much to be gained by
two decades or so of living at home—even if this arrangement is at times
inconvenient for child and parent alike.
In
the following sections, we will consider three major aspects of development,
including the infant’s sensorimotor development, her cognitive development, and
her socioemotional development. We should be clear at the outset that the
distinctions among these aspects of development are, to some extent, just a convenience
for researchers (and textbook writers), because the various aspects of
development plainly interact with each other. The child’s intellectual
development, for example, is shaped by what she perceives and how she interacts
with the world. Similarly, the child’s socioemotional development depends on
her cognitive development, and vice-versa.
A
similar point must be made regarding the interplay of genetic and environmental
factors. These, too, constantly interact to codetermine a child’s developmental
trajectory. For example, we mentioned that genetic factors are cru-cial for
shaping a child’s intellectual functioning, but as we discussed, the
environment also plays a huge role. Some environmental factors are biochemical
(nutrients, toxins), and one tragic reminder of this comes from studies of
mental retar-dation. For years, many types of paint contained lead-based
pigments, and as the paint deteriorated, leaded dust would fall into the
environment where it could be ingested or inhaled by children. Once inside the
body, the lead interfered with the development of the nervous system, at large
doses causing coma or even death, or at lower doses producing a litany of
intellectual problems that often led to a diagnosis of mental retardation. This
is why lead paint was banned for use in U.S. residences in 1978; other
countries have similar (and older) bans in place.
Environmental
influences also have other—and more positive—effects on the developing nervous
system. Stimulus information—including objects to explore or manipulate, other
organisms to interact with, and so on—seems by itself a spur to neural growth.
In addition, the specifics of the stimulation help to refine the nervous
system’s functioning—so that the visual system, for example, becomes especially
sensitive to the specific shapes in the infant’s environment; circuits involved
in language use are likewise adjusted so that the neural apparatus for
understanding and producing language is pre-cisely tuned to the language being
spoken in the child’s surroundings.
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