Life Expectancies
| Humans by Era | Longevity* | Comment |
| Upper Paleolithic | 33 | At age 15: to age 54 (39) |
| Neolithic | 20 | |
| Bronze Age and Iron Age | 35+ | |
| Classical Greece | 28 | At age 15: to age 52 (37) |
| Pre-Columbian North America | 25-30 | |
| Medieval Islamic Caliphate | 35+ | |
| Medieval Britain | 30 | At age 21: to age 59 (38) |
| Early Modern Britain | 30-45 | |
| Current world average | 67.2 | 2010 est. |
* Longevity: Average Lifespan at Birth (years)
Life Expectancy – What is Life Expectancy?
http://www.news-medical.net/health/Life-Expectancy-What-is-Life-Expectancy.aspx
Life expectancy is the expected (in the statistical sense) number of years of life remaining at a given age. It is denoted by e”x”, which means the average number of subsequent years of life for someone now aged ”x”, according to a particular mortality experience.
In technical literature, this symbol means the average number of ”complete” years of life remaining, excluding fractions of a year. The corresponding statistic including fractions of a year, the normal meaning of life expectancy, has a symbol with a small circle over the ”e”.
The life expectancy of a group of individuals is heavily dependent on the care.
The term that is known as life expectancy is most often used in the context of human populations, but is also used in plant or animal ecology; it is calculated by the analysis of life tables (also known as actuarial tables).
The term life expectancy may also be used in the context of manufactured objects and 49.0 years in Japan (2008 est.), although Japan’s recorded life expectancy may have been very slightly increased by counting many infant deaths as stillborn.