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Notice that the life expectancy is heavily dependent on the criteria used to select the group. In countries with high infant mortality rates, the life expectancy at birth is highly sensitive to the rate of death in the first few years of life. In these cases, another measure such as life expectancy at age 10 can be used to exclude the effects of infant mortality to reveal the effects of other causes of death. Usually, though, life expectancy at birth is specified. To calculate it, it is assumed that current mortality levels remain constant throughout the lives of the hypothetical newborns.
Life expectancy has dramatically increased over the last few centuries of human history. These changes are largely the result of improvements in public health, medicine and nutrition. The greatest improvements have been made in the richest parts of the world, but the same effects are now spreading to other parts of the world as their economies and infrastructure improve.
Life expectancy increased dramatically in the 20th century, especially in developed nations. Life expectancy at birth in the United States in 1901 was 49 years. At the end of the century it was 77 years, an increase of greater than 50%. Similar gains have been enjoyed throughout the world. Life expectancy in India and The People's Republic of China was around 40 years at midcentury. At century's close it had risen to around 63 years. These gains were due largely to the eradication and control of numerous infectious diseases and to advances in agricultural technology (such as chemical fertilizers).
Basic life expectancy numbers tend to exaggerate this growth, however. The low level of pre-modern life expectancy is distorted by the previous extremely high infant and childhood mortality. If a person did make it to the age of forty they had an average of another twenty years to live. Improvements in medicine, public health and nutrition have therefore mainly increased the numbers of people living beyond childhood, with less effect on overall average lifespan.
These improvements continue to confound the predictions of Thomas Malthus, who predicted what is now known as the Malthusian catastrophe which would occur when population growth exceeded the capacity of the world to sustain that population.
The major exception to this general pattern of improvement has been in those countries worst hit by AIDS, principally in Sub-Saharan Africa, which have seen significant falls in life expectancy due to the disease in recent years.
Another exception is Russia and other former USSR republics after the collapse of the Soviet Union. Life expectancy of men dropped to 59.9 years (below the official retirementRetirement is the status of a worker who has stopped working. This usually happens upon reaching a determined age, when physical conditions don't allow the person to work any more (by illness or accident), or even for personal choice (usually in the prese age), of women to 72.43 years (1999).
In recent years, obesityObesity is a condition in which the natural energy reserve of a mammal (such as a human), which is stored in fat, is expanded far beyond usual levels to the point where it causes health stress. Obesity in wild animals is relatively rare, but it is common-correlated diseases have become a major public health issue in many countries. The prevalence of obesity is thought to have reduced a potential for longer life expectancy by contributing to the rise of cancers, heart disease and diabetes in the developed world.
Throughout human history most of the increase in life expectancy arose from preventing early deaths. However, many scientists believe this will not stay true in the future, as it will be possible to revert aging. According to Leroy HoodLeroy Hood won the 2003 Lemelson-MIT Prize for inventing "four instruments that have unlocked much of the mystery of human biology" by helping decode the genome. Hood also won the 2002 Kyoto Prize for Advanced Technology, and the 1987 Lasker Award for Stu, the life expectancy in the next three decades will increase by 10-20 years thanks to advances in DNA sequencing and nanotechnologyNanotechnology as a collective term refers to technological developments on the nanometre scale, usually 0. One nanometre equals one thousandth of a micrometre or one millionth of a millimetre. The term sometimes applies to any microscopic technology.. Some scientists believe that further advances in medical science may push life expectancy even further, effectively making humans immortalImmortality is the concept of existing for a potentially infinite or indeterminate length of time. Throughout history humans have had the desire to live forever. The most commonly conceived form of immortality involves a spiritual existence after physical.
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