Life expectancy

We can guess how long people live.

Long ago, people died much younger. In the Bronze Age, the average was 24. Many children died back then.

Today, people live much longer. In 2019, the world average was about 73. This is much higher.

Better health helps people live. New ways to stay well make a big difference. These changes help us live more years.

One woman lived to be 122. That is the longest life ever found. It is a very big number!

How long will a person live? We can estimate this using life expectancy. This is an average number of years. It is not a rule for one person.

Life expectancy changes over time. In the Bronze Age, the average was 24 years. Many children died young back then. This makes the average number look low. In 2019, the world average was 73.3 years. This is much higher than before.

Public health helps people live longer. These are ways to keep people well. Better medicine and clean water help a lot. In the United States, health ways added 25 years to life.

Some words sound the same but are different. Longevity means living a long life. Maximum lifespan is the oldest age ever reached. One woman, Jeanne Calment, lived to 122 years.

Life expectancy can also be for animals. It can even be for things we make. Engineers study how long a tool works before it breaks.

Life expectancy is a way to estimate how long people might live. It is a statistical measure of the average remaining years of life at a certain age. Most people use the term life expectancy at birth, often called LEB. This number is an average, not a rule for every person. Some people may die much sooner than the average. Others may live many years longer than the expected number.

There are two main ways to look at this number. One way is called cohort LEB. This tracks the mean length of life for everyone born in one specific year. This can only be found once every person in that group has died. The other way is called period LEB. This uses the death rates seen in one single year to make a guess. It assumes a group of people would face those same rates from birth to death. Most national and international reports use period LEB to show current trends.

People have been studying these patterns for a long time. The earliest documented work on life expectancy happened in the 1660s. This work was done by John Graunt and the Huygens family. Christiaan Huygens and Lodewijck Huygens both helped with these early studies. Since then, our understanding of how long humans live has changed a lot. We can now see how much life expectancy has grown over many centuries.

History shows us how much life has changed. In the early Bronze Age, the LEB was only 24 years. Many people died young from accidents, wars, or sickness. In 2019, the world LEB rose to 73.3 years. In the 19th century, the world average was between 28.5 and 32 years. In the United States, public health advances added 25 years to life.

It is helpful to know the difference between similar words. Longevity refers to the long lifespans of some people in a group. Maximum lifespan is the oldest age any human has ever reached. A French woman named Jeanne Calment holds this record. She lived to be 122 years and 164 days old. We also use life expectancy to study animals or even machines. For tools, engineers use terms like mean time to breakdown.

Life expectancy is a statistical estimate of the average number of years a person is expected to live. It is a vital tool used by scientists to understand how healthy a population is. Most researchers focus on life expectancy at birth, often called LEB. This measure helps us see how much human life has changed over time. It is important to remember that life expectancy is an average. This means an individual person may live many years more or many years less than the predicted number.

There are two distinct ways to calculate this measurement. The first method is called cohort LEB. This calculates the mean length of life for every person born in one specific year. This can only be completed once every member of that birth group has died. The second method is period LEB. This uses the mortality rates observed during one specific year to create a hypothetical model. It assumes a group of people would face those exact same death rates from birth until their death. Most national and international agencies report period LEB to show current trends.

Understanding the mechanism of life expectancy requires looking at how different ages affect the numbers. Life expectancy is highly sensitive to infant mortality. This refers to the rate of death in the first few years of life. Because of this, a low LEB can be misinterpreted. A low number might suggest a population has very few old people, but it often just means many infants died. To get a clearer view, researchers may use life expectancy at age 5. This excludes the effect of early childhood deaths to show other mortality rates.

It is also helpful to distinguish life expectancy from other similar terms. Longevity refers to the relatively long lifespans of certain members within a population. Maximum lifespan is the highest age reached by any single individual of a species. For example, the longest verified human lifespan belonged to Jeanne Calment. She was a French woman who lived to be 122 years and 164 days old. While the maximum life expectancy is thought to be around 125 years, some suggest genetic enhancements could reach 245 years. However, a theoretical study suggests a limit of about 104 years based on human characteristics.

History shows a massive increase in these numbers over thousands of years. In the early Bronze Age, the LEB was only about 24 years. During the Classical Greece era, it was between 25 and 28 years. In Ancient Rome, many children died before reaching adolescence. If a Roman survived to age 20, they could expect to live about 30 more years. By the beginning of the 19th century, no country had a life expectancy at birth longer than 40 years. In contrast, the world LEB reached 73.3 years in 2019.

Significant changes occurred during the Industrial Revolution and the 20th century. In London, deaths of children under age 5 fell from 74.5% in the 1730s to 31.8% by the 1820s. In the United States, the average lifespan increased by more than 30 years during the 1900s. About 25 of those years were due to advances in public health. Public health measures are a major reason for the recent global increase in longevity. These improvements help prevent the spread of disease and improve nutrition.

Life expectancy is a concept used in many different fields beyond human biology. In plant or animal ecology, scientists use it to study the lifespans of different species. It is also used in the creation of life tables, which are also called actuarial tables. Even engineers use a similar concept for manufactured objects. Instead of life expectancy, they use terms like mean time to breakdown or mean time between failures. This shows how the idea of expected duration applies to almost everything in our world.