There is no consistency in estimates of how long people have lived throughout history. This is largely because, prior to around 1500 Common Era, birth and death records were rare -- usually only available for royalty or others who had influence and power. The everyday person's birth and death were remarked upon only by friends and family.
In general, however, it is considered that the overall life expectancy has increased over the years. One set of estimates indicates around 25 to 30 years old in BCE, rising to 30 to 40 years old in the 1500 to 1800 and then ballooning up past the 1800s to current world expectancy of 65 to 75.
Life expectancy is a statistical measurement as to the AVERAGE life span for a larger population. This number can vary between regions of the world, countries, or even counties. In the previous paragraph, I was talking about global numbers. An individual's life span is dependent on different factors. Some of these factors are not under anyone's control, some are "per chance", and some are voluntary risks.
The primary factor for life span is how long your ancestors lived -- your genetic heritage. Robert A. Heinlein did a great job going into this in his book Methuselah's Children. This is the baseline -- something that we presently cannot change and which gives the maximum time our bodies have to be around without becoming zombies. Some people believe that this can be extended by various means but, in my opinion, it is really a matter of eliminating the many factors that can shorten this period -- the maximum has not truly changed.
We have succeeded in helping to prevent some events that shorten life -- which is why our global life expectancy has increased. One of the biggest boosts in overall global life expectancy has been from medical advances that have decreased infant and mother mortality. If a quarter of all children die before they are two years old, it decreases average life span (and population life expectancy) considerably. This is also a large part of why the life expectancy of women is now higher than that of men and why it used to be the other way around. Other medical advances and general sanitation have been the other primary method to avoid life shortening events.
So what are the common life shortening effects? War (and murder) is a huge one and one which historically has taken a greater direct toll on the expectancy of men. Drought and famine change localized life expectancy. Lack of nutritious food early in life can also affect health later in life even if food is then available. Death by disease has been reduced by immunizations, treatments, sanitation, and recognition and isolation. Finally, death by accident is with us and seems to be impossible to totally avoid.
Voluntary risks do not really add to the life shortening lists -- they just make them more likely to occur. Smoking, for example, can increase the chance for disease if one is genetically likely to get the disease -- a trigger effect rather than a causal one. Enjoying a dangerous hobby -- parachuting, mountain climbing, car racing -- can increase the chance for accidents.
Note that deliberately avoiding risks can sometimes actually increase shortening effects. For example, the overuse of antibiotics is increasing the likelihood of disease by making the diseases stronger as well as decreasing our immune systems' ability to fight disease. Living "in a bubble" (isolated) may decrease the chance of accidents and disease while one is "in the bubble" but it makes us even more vulnerable when we are no longer isolated.
So, aside from choosing our parents (which isn't possible), we can best increase life expectancy by having cooperative societies (lack of war and murder), producing and distributing nutritious food and healthy water, building up strong immune systems, and making reasonable choices to avoid preventable accidents and diseases. We still won't live forever but do we want to?
The next blog will address the downside of living a long life.
