W
hen does a teenager become capable
of thinking like an adult? The case of
Miller v. State of Alabama shows that this
is not just an academic question; it can be
a matter of life or death. For that matter,
when does a teenager become an “adult”?
What factors in a person’s biology, learning,
and environment define adulthood? Why do
some 14-year-olds seem “all grown up” and
some adults never do?
Throughout history and across cultures,
the answers have varied widely. In some so-
cieties and eras, even young children were
regarded as “little adults”; the idea that
childhood is a distinct phase of development
was unheard of. (In paintings, children even
looked like adults—just smaller.) Similarly,
for most of human history, the idea that ado-
lescence is a special phase of life would have
been considered preposterous. Before the
Industrial Revolution, children and teenagers
worked alongside adults on farms; in cities,
they were sent to work as apprentices or ser-
vants, doing whatever job they could get.
Then, during the twentieth century, “age
consciousness” emerged. Childhood came
to be viewed as a period when powerful for-
mative experiences determined the kind of
adult a child would become. Adolescence
became a distinctive stage between the
physical events of puberty and the social
markers of adulthood. Adults, whose lives
once had proceeded in a predictable way
(school, job, marriage, parenthood, retire-
ment), began to do these things “out of or-
der.” Old people were increasingly separated
from the rest of society on the grounds that
they could not keep up with the fast-moving
world—and the definition of “old” began
changing, from 60 to 70 to beyond. These
changes have made questions about “age-
appropriate” behavior and people’s respon-
sibility for their actions more complicated.
Developmental psychologists address
such issues by studying universal aspects of
3 Development over the life span
variations, and differences among individu-
als. Some focus on children’s mental and
social development, including socialization,
the process by which children learn the
rules, attitudes, and behaviors expected of
them by society. Others specialize in the
study of adolescents, adults, or the old. In
this chapter, we will explore some of their
major findings, starting at the beginning of
human development, with the period before
birth, and continuing through adulthood
into old age. At the end of the chapter, you
will find out how the Supreme Court ruled
in the case of Evan Miller, what kind of psy-
chological evidence contributed to that de-
cision, and what factors might have caused
the teenagers to commit the crime they did.
You are about to learn...
• the course of prenatal development and some
factors that can harm an embryo or fetus.
• how culture affects a baby’s physical
maturation.
• why contact comfort and attachment are
essential for infants (and adults).
• the varieties of infant attachment.From Conception
Through the First Year
Lo 3.1, Lo 3.2
A baby’s development, before and after birth, is
a marvel of maturation, the sequential unfolding
of genetically influenced behavior and physical
characteristics. In only nine months of a mother’s
pregnancy, a cell grows from a dot this big (.) to
a squalling bundle of energy who looks just like
Aunt Sarah. In another 15 months, that bundle of
energy grows into a babbling toddler who is curi-
ous about everything. No other time in human
development brings so many changes so fast.Prenatal Development
Prenatal development begins at fertilization, when
the male sperm unites with the female ovum (egg)
to form a single-celled egg called a zygote. The
zygote soon begins to divide, and in 10 to 14 days,
it has become a cluster of cells that attaches itself
to the wall of the uterus. The outer portion of this
cluster will form part of the placenta and umbilical
cord, and when implantation is completed, about
two weeks after fertilization, the inner portion
becomes the embryo. The placenta, connected to
the embryo by the umbilical cord, serves as thesocialization The pro-
cesses by which children
learn the behaviors,
attitudes, and expecta-
tions required of them by
their society or culture.