BACKGROUND:
Body proportions change remarkably from birth to maturity.
At birth, a baby's head is one-fourth the size of the body, the forehead
is wider than the chin, the lower jaw is small and receding. Growth
lengthens the limbs and trunk so that at about two years of age the general
body configuration is longer and thinner and the head is about one fifth
the size of the body. At six years of age, the body has stretched
out further so that the head occupies about one-sixth of its length.
The tendency for linear growth continues until puberty when the body tends
to broaden relative to height. At about age 15 the head is one-seventh
the size of the body which is maintained through life.
PROCEDURE:
- Give your students the "baby" worksheet.
Ask the students if they think babies have the same body parts as adults
(Yes). Ask the students if there are any differences between a baby's
body and an adult's body? (Yes, the head is proportionally larger in a
baby's.)
- Although this is a cartoon of a baby, it shows that one
obvious difference, the size of the head appears out of proportion with
the rest of the body. Ask your students if they believe this cartoon
is accurate. Ask them to remember what a baby looks like and have
them visually compare the body size with the head size.
- For a homework assignment see if the students can find
out at what time a child's body is in proportion with its head. Have
the students ask their parents or observe their younger sisters, brothers,
or friends. Record this information on the lab sheet. This usually
occurs about 5-8 years.
- After you tabulate what students have observed, see if
they can figure out why. The brain size of a baby during the time
in which it is developing inside the mother tells the mother's body when
it's time for the new baby to emerge. The rest of the body has not
kept pace with the rapidly growing head.
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