In general, as soon as the newborn child’s muscles, sense
organs, and nerves are fully formed, the child begins to use them. But much of
the human nervous system is not fully developed until the child is a year or two
old, and some parts, such as the corpus callosum, continue to mature for at
least the next 20 years. The general pattern of bodily
development is from head to foot. Simple skills, such as head movements, appear
first because the structures that control these skills are among the first to
mature. More complex behavior patterns, such as crawling, standing, and walking,
come much later in the developmental sequence than head movements do.
The motor centers in the brain are connected by long nerve fibers
(usually through one or more synapses) to the muscles in various parts of the
body. Since the head muscles are closer to the brain than the foot muscles,
according to one theory, the head comes under the control of the motor centers
long before the feet do. The appearance of a new motor skill (such as crawling
and grasping) always suggests that a new part of the child’s body has just
matured-that is, that the brain centers have just begun to control the muscles
involved in the new motor skill. What is the author’s main purpose in this passage
A.To describe how children crawl, stand, and walk.
B.To explain why some children are slow to develop.
C.To describe early physical development in children.
D.To explain the function of the corpus callosum.