Sources of Developmental Change
The issue of "why" lies behind every developmental
study or theory. Whether one
studies development
observationally or
experimentally,
cross-sectionally or
longitudinally, within a
stage-based or an
incremental theoretical framework, the central
question remains: What is the source of development
change? The answer to this
question has important consequences not only for
our understanding of development but
also for the kinds of strategies we should pursue
to solve real-world problems.
Genes
The structures of our bodies and brains are largely
determined by the kinds of genes we
have. Thus it is tempting to look to genes as the
source of the changes in those structures,
and in the behaviors they cause, over the course of
the life span. Few would deny that
genes have a large role to play in the increases in
height, weight, strength, and other
physical attributes that we see during childhood.
More controversial, but quite prevalent, is the
conclusion that mental abilities are similarly
influenced by genes.
Environment
In contrast to gene-based explanations, many have
argued that the environment is the
primary cause of developmental change. Support for
this claim comes from the wide
range of studies that show that experience in the
world is crucial for any kind of
development, and that differences in the
environment can have enormous consequences
for the direction of development. Perhaps the most
important part of the environment is
the social environment: the people with whom the
child interacts on a daily basis.
The Interactionist Approach
Between the extremes of genetic and environmental
approaches to development is a
middle ground: the interactionist approach.
According to this approach, development
arises from a combination of genetic and
environmental factors. Throughout the life
course, genetics obviously have an important role
to play in influencing behavior;
however, the exact effect they have depends on
one's current environment and past
experiences. The biology of genes are also
strongly influenced by behavior; for instance,
stress hormones and many other brain chemicals
whose levels are influenced by the
environment can cause changes in the expression of
genes in the brain and even in the
growth of different parts of the brain.
