Graphics Reference
In-Depth Information
that do occur between some races of people are of an environmental and
geographic nature. Differences can be found between people that are
indigenous to mountainous regions and those living at sea level. Due to
the lack of oxygen at higher altitudes, people living in high mountainous
regions have developed a greater capacity to breathe much thinner air than
people living at sea level. For this reason, athletes from low-lying countries
need to acclimatize themselves to conditions at high altitude before they can
compete at their optimum performance in such regions.
Unlike the babies of many mammals, the human baby remains vulnerable and
dependent on its mother for care and nourishment for an extended period
after birth. Some quadrupeds are up on their feet and running within the
hour. Human babies take much longer to get around under their own steam.
Human babies generally begin to crawl at somewhere between six and seven
months old, and it takes them around a year before they begin to walk. To
walk steadily and with confidence may take many months more.
The physiognomy of the human body changes throughout our lives. Initially the
body lacks strength and does not have the capacity to support itself, though it
is very flexible. We have all seen with what ease a baby can place its toes in its
mouth. We are born with very large heads compared with the size of our bodies,
but as we grow through childhood and into adulthood the proportion of the
head to body size changes.
Having gained confidence with walking, children continue to develop
and learn to run, jump, and hop, along with a variety of other modes of
locomotion. As we grow we also become increasingly dexterous and we
develop a capability to use tools.
Growth continues until a point between 20 and 25 years, when we complete
the process that replaces with bone any of the parts of our skeletal structure
that began as cartilaginous and are destined to become ossified. Once this
process stops, no more growth occurs.
It is normal for individuals to physically deteriorate as the body begins to age.
As we grow older we experience a loss of calcium, which results in our bones
becoming porous and brittle. Some of this loss is due to the aging process and
is perfectly natural. However, serious loss of calcium may occur as a result of
a condition known as
osteoporosis
. For people that have this condition, it can
become a serious issue, particularly if it affects weight-bearing bones or bones
used in muscle pull actions. It is not uncommon for brittle bones to result in
falls and injury. As an individual becomes increasingly frail and less strong,
through either the natural aging process or illness, the impact on mobility
increases. Osteoporosis occurs in women more often than men.
Physical differences in individuals clearly make a difference in the
performance of certain tasks, and of course there are obvious differences
between the genders. Women have larger hips and narrower shoulders than
men, and in very general terms men are stronger than women.
