Chapter 16: Regulation and Reproduction

Figure 15 Human babies
are more dependent upon their
caregivers than many other
mammals are.
Infants and toddlers are completely dependent upon
caregivers for all their needs.
484 CHAPTER 16 Regulation and Reproduction
(l)Jeffery W. Myers/Stock Boston, (r)Ruth Dixon
Stages After Birth
Defined stages of development occur after birth, based on
the major developments that take place during those specific
years. Infancy lasts from birth to around 18 months of age.
Childhood extends from the end of infancy to sexual maturity,
or puberty. The years of adolescence vary, but they usually are
considered to be the teen years. Adulthood covers the years of
age from the early 20s until life ends, with older adulthood considered
to be over 60. The age spans of these different stages are
not set, and scientists differ in their opinions regarding them.
Infancy What type of environment must the infant adjust to
after birth? The experiences the fetus goes through during birth
cause fetal stress. The fetus has emerged from an environment
that was dark, watery, a constant temperature, and nearly
soundless. In addition, the fetus might have been forced through
the constricted birth canal. However, in a short period of time,
the infant’s body becomes adapted to its new world.
The first four weeks after birth are known as the neonatal
(nee oh NAY tul) period. The term neonatal means “newborn.”
During this time, the baby’s body begins to function normally.
Unlike the newborn of some other animals, human babies, such
as the one shown in Figure 15, depend on other humans for
their survival. In contrast, many other animals, such as the
young horse also shown in Figure 15, begin walking a few hours
after they are born.
Other young mammals are more self-sufficient. This colt
is able to stand within an hour after birth.