It is only in the past two centuries where demographics and the development of human populations has emerged as a subject in its own right, as industrialization and improvements in medicine gave way to exponential growth of the world's population. There are very few known demographic studies conducted before the 1800s, which means that modern scholars have had to use a variety of documents from centuries gone by, along with archeological and anthropological studies, to try and gain a better understanding of the world's demographic development. Genealogical records One such method is the study of genealogical records from the past; luckily, there are many genealogies relating to European families that date back as far as medieval times. Unfortunately, however, all of these studies relate to families in the upper and elite classes; this is not entirely representative of the overall population as these families had a much higher standard of living and were less susceptible to famine or malnutrition than the average person (although elites were more likely to die during times of war). Nonetheless, there is much to be learned from this data. Impact of the Black Death In the centuries between 1200 and 1745, English male aristocrats who made it to their 21st birthday were generally expected to live to an age between 62 and 72 years old. The only century where life expectancy among this group was much lower was in the 1300s, where the Black Death caused life expectancy among adult English noblemen to drop to just 45 years. Experts assume that the pre-plague population of England was somewhere between four and seven million people in the thirteenth century, and just two million in the fourteenth century, meaning that Britain lost at least half of its population due to the plague. Although the plague only peaked in England for approximately eighteen months, between 1348 and 1350, it devastated the entire population, and further outbreaks in the following decades caused life expectancy in the decade to drop further. The bubonic plague did return to England sporadically until the mid-seventeenth century, although life expectancy among English male aristocrats rose again in the centuries following the worst outbreak, and even peaked at more than 71 years in the first half of the sixteenth century.

In Asia, the highest levels of life expectancy were found in East Asia, reaching 76 years for men and 82 years for women. The lowest levels were found in South Asia.

What is life expectancy

Life expectancy is, in the statistical sense, the number of years to be lived. It is the most common measure to describe population health. The life expectancy is an average and a person may die several years before or several years after their expected survival.

Economic circumstances also affect life expectancy. Life expectancy in the wealthiest countries is higher than in the poorest areas. With a life expectancy of 84 years, Japan, Liechtenstein, Switzerland, and South Korea lead the ranking of the 20 countries with the highest life expectancy as of 2021. The countries with the lowest life expectancy in 2021 were Chad, Nigeria, and Lesotho.

Gender and life expectancy

The gender differences in life expectancy are significant. Women tend to live several years longer than men. The average life expectancy worldwide of those born in 2023 shows that women had an average life expectancy of 75 years at birth, while men were expected to live 70 years.