A water treatment plant in eastern France. Clean water is one of history's greatest lifesavers. (Photo: FREDERICK FLORIN/AFP/Getty Images)
Here's a statistic that gets more incredible the more you think about it: over the past 150 years, the average lifespan in developed countries has doubled, from about 35 years to about 80. As Laura Helmuth puts it in a fascinating feature on Slate today, "We used to get one life. Now we get two."
Here, five reasons Helmuth gives for the remarkable new longevity in the developed world (which doubles a short-list for how to improve lifespan in the developing one):
At the close of the 17th century, an estimated 400,000 Europeans died of smallpox each year — about one in 500. But following widespread vaccination campaigns, that number dropped to zero. As Helmuth points out, "vaccines have been so effective that most people in the developed world don't know what it's like to watch a child die of pertussis or measles" — a phenomenon that used to be distressingly common.
4. Proper Nutrition
In the late 1800s, people in rural America lived about 10 years longer than city folk, and a big part of that was because of their superior nutrition. Indeed, this difference in food supply meant that farmers were on average taller than labourers. When food was available, it was often contaminated, a problem that was slowly addressed by refrigeration, pasteurization and laws against selling adulterated food.
3. Adequate Housing
In the late 19th century, city centres were often crowded and filthy, with poor ventilation — making them perfect breeding grounds for microbes. Tuberculosis was particularly rampant in urban environments. As the 19th century gave way to the 20th, bigger, airier housing was built and much of the older housing was destroyed, all of which made life harder for pests and germs alike.
2. The germ theory of disease
For most of human history, people did not understand how most diseases were spread: the "miasma" theory blamed clouds of "bad air" instead of the micro-organisms we now know are responsible for most illness. Once the germ theory of disease spread, so did soap and hand washing. "Soap stops both deadly and lingering infections," writes Helmuth. "Even today, kids who don't have access to soap and clean water have stunted growth."
1. Clean water
This is the big one: Helmuth writes that some historians credit clean drinking water for reducing overall mortality in half, child mortality by two thirds and infant mortality by a full three quarters. Early attempts to purify water involved passing it through sand and gravel to trap dirt, followed by wholesale chlorination of the water supply starting in the early 1900s. Nearly as important were projects to keep sewage water and drinking water completely separate — incredibly, sewage outlets were often placed right next to drinking water inlets in many cities.