This article was adapted from
Developmental
Psychology
By
Grace
A. Adejuwon Ph.D.
Department of Psychology
University of Ibadan
Heredity: This consists
of inborn influences on development carried on the genes inherited from the
parents. The basic unit of heredity is the gene. Genes contain all the
hereditary material passed from biological parents to children which affects
inherited characteristics. Each cell in the human body contains an estimated
80,000 to 100,000 genes. The gene is made up deoxyribonucleic acid (DNA). The
chromosomes carry the genes. There are 23 pairs (46) of chromosomes in each
cell except the sex cells of the body. The sex chromosomes are either X
chromosome or Y chromosome. The ovum of the woman contains XX chromosomes while
the sperm of the man contain XY chromosomes. After fertilization, the child
will be a boy if the Y chromosome from the man fertilizes the X- carrying ovum,
forming XY zygote while a girl will be formed if the X chromosome from the man
fertilizes the X-carrying ovum of the woman forming XX zygote. Other inherited
characteristics give each child a unique start in life.
Environment: This is the
totality of nongenetic influence on development external to the self. It
includes family, socioeconomic factors, ethnicity and culture. Family may mean
something different in different societies. The types of family include nuclear
family, extended family, single-parent family and step-families. The nuclear
family is a two-generational kinship consisting of two parents and their
biological or adopted children. The extended family is a multigenerational
kinship network of parents consisting of children, parents, grandparents,
uncles, aunties, cousins and other relatives forming in an intimate relationship
with the child. Some of the time the extended family lives in the same
household.
Socioeconomic Status (SES)
This
involves a variety of related factors including income, education, and
occupation. Socioeconomic factors have been found in many studies to be
associated with developmental outcomes such as health, cognitive performance,
and differences in mother’s verbal interaction with their children. However, it
is not SES itself that directly affects these outcomes but factors associated
with SES such as the kind of home and neighbourhood a child lives in and the
quality of medical care and schooling a child receives.
Mechanisms
of Development
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Ethnic Group
An
ethnic group consists of people united by ancestry, race, culture, language,
and/ or national origins which contribute to a sense of shared identity.
Culture refers to a society’s way of life including customs, traditions,
believes, values, language and physical products from tools to art works and
all of the learned behaviour that is passed from adults to children. Culture is
not static; it is constantly changing most of the time through interaction with
other cultures.
Maturation
This
is when sequence of physical changes and behaviour patterns, including
readiness to master new abilities unfolds. Maturation is genetically influenced
and often age-related. For example, as children grow into adolescents and then
into adults, differences in innate characteristics and life experience play a
greater role.
Normative
and Non-normative influences
Normative
An
event is normative when it occurs in a similar way for most people in a group.
Some may be age-graded or history-graded. Normative age-grade influences are
highly similar for people in a particular age group. They include biological
events such as puberty, and cultural events such as entry into formal
education. Normative history-graded influences are common to a particular
cohort ( a group of people who share similar
experiences such as growing up at the same time and in the same place).
Children may also feel the impact of war, famines, nuclear explosions, and
economic depressions depending on where they live and when the occurrence took
place. For example, most children are affected by the widespread participation
of women in the work force in Nigeria today.
Nonnormative
These
are unusual life events that have a major impact on individual lives and may
cause stress because they are unexpected. They are typical events that happen
at a typical time of life such as; death of a parent when a child is young or
death of spouse at an unexpected period of marital life. They may also be
events such as being involved in a motor crash, having a birth defect. They can
also be happy events such as winning a scholarship. Some people create their
own Nonnormative life events such as driving when drunk or applying for a
scholarship or making every effort to pass an examination.
Timing of influence: Critical or
Sensitive Periods
Certain
events should occur at particular times in the course of human development-
this is called the critical time for that particular event. A critical time
refers to a specific time during which a given event will have the greatest
impact on development. For example, if a pregnant woman is exposed to X-rays,
contact certain diseases, or takes certain drugs at specific times, the foetus
may develop specific ill effects. The extent of damage will vary depending on
the timing of those events. Also, the period just after birth is critical for
brain growth. Undernourishment just after birth can result in brain damage.
Giving an infant an opportunity to practice stepping movements during the first
week of life may lead to early walking. Also, the first three years of life may
be critical to developing ability to focus the eyes (binocular vision). As such
a physical problem such as crossed eyes if not corrected during that period may
interfere with the proper development of binocular vision. Mutual face-to- face interaction with an
adult in the first six months of life is critical to the development of
circuits in the brain which regulates emotional excitement.
However, although the human organism may
be particularly sensitive to certain psychological experiences at certain
times, later events can reverse the effects of earlier ones. For example, a
child who becomes attached to the mother early in life may become insecure at
adolescence if the child is exposed to adverse situations. In other words, the performance of cognitive
and psychosocial development may be modifiable. This means that there is
greater plasticity in performance for these aspects of development.
Mechanisms
of Development
Although
developmental change runs parallel with chronological age, age itself cannot
cause development. The basic mechanisms or causes of developmental change are
genetic factors and environmental factors. Genetic factors are responsible for
cellular changes like overall growth, changes in proportion of body and brain
parts, and the maturation of aspects of function such as vision and dietary
needs. The individual's initial genotype
may change in function over time, giving rise to further developmental change.
Environmental factors affecting development may include diet and disease
exposure, as well as social, emotional, and cognitive experiences. However,
examination of environmental factors also shows that young human beings can
survive within a fairly broad range of environmental experiences.
Rather than acting as independent
mechanisms, genetic and environmental factors often interact to cause
developmental change. Some aspects of child development are notable for their
plasticity, or the extent to which the direction of development is guided by
environmental factors as well as initiated by genetic factors. For example, the
development of allergic reactions appears to be caused by exposure to certain
environmental factors relatively early in life, and protection from early
exposure makes the child less likely to show later allergic reactions. When an
aspect of development is strongly affected by early experience, it is said to
show a high degree of plasticity; when the genetic make-up is the primary cause
of development, plasticity is said to be low. Plasticity may involve guidance
by endogenous factors like hormones as well as by exogenous factors like
infection.One kind of environmental guidance of
development has been described as experience-dependent plasticity, in which
behavior is altered as a result of learning from the environment. Plasticity of
this type can occur throughout the lifespan and may involve many kinds of
behavior, including some emotional reactions. A second type of plasticity,
experience-expectant plasticity, involves the strong effect of specific
experiences during limited sensitive periods of development. For example, the
coordinated use of the two eyes, the experience of a single three-dimensional
image, rather than the two-dimensional images created by light in each eye,
depend on experiences with vision during the second half of the first year of
life. Experience-expectant plasticity works to fine-tune aspects of development
that cannot proceed to optimum outcomes as a result of genetic factors working
alone. In addition to the existence of
plasticity in some aspects of development, genetic-environmental correlations
may function in several ways to determine the mature characteristics of the
individual. Genetic-environmental correlations are circumstances in which
genetic factors make certain experiences more likely to occur. For example, in
passive genetic-environmental correlation, a child is likely to experience a
particular environment because his or her parents' genetic make-up makes them
likely to choose or create such an environment. In evocative
genetic-environmental correlation, the child's genetically-caused
characteristics cause other people to respond in certain ways, providing a
different environment than might occur for a genetically-different child; for
instance, a child with Down syndrome may be treated more protectively and less
challengingly than a non-Down child. Finally, an active genetic-environmental
correlation is one in which the child chooses experiences that in turn have
their effect; for instance, a muscular, active child may choose after-school
sports experiences that create increased athletic skills, but perhaps preclude
music lessons. In all of these cases, it becomes difficult to know whether
child characteristics were shaped by genetic factors, by experiences, or by a
combination of the two.
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