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Teacher Background
Life Span
vs. Life Expectancy
According to
The National Institute on Aging :
There are "two kinds
of life span. One is maximum life span, the greatest age reached
by any member of a species. In humans this is 120 years, we think.
The other is average life span, the average age reached by members
of a population. Life expectancy, the number of years an individual
can expect to live, is based on average life spans.
Average life span and
life expectancy in the United States have
grown dramatically in this century, from about 47 years in 1900
to
about 75 years in 1990. This advance is mostly due to improvements
in sanitation, the discovery of antibiotics, and medical care. Now,
as
scientists make headway against chronic diseases like cancer and
heart disease, some think it can be extended even further.
Maximum human life span
seems to be another matter. There is no
evidence that it has changed for thousands of years despite fabled
fountains of youth and biblical tales of long-lived patriarchs.
However, very recently, the dream of extending life span has shifted
from legend to laboratory. As gerontologists explore the genes,
cells,
and organs involved in aging, they are uncovering more and more
of
the secrets of longevity. As a result, life extension may now be
more
than the stuff of myth and the retardation of disease and disability,
realistic goals."
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