Life expectancy is commonly misunderstood. First, the full term is actually "average life expectancy". It was low because the huge number of child deaths simply

Life expectancy is commonly misunderstood. First, the full term is actually "average life expectancy". It was low because the huge number of child deaths simply drove down the average of the whole population. People frequently lived way into their 70s or 80s or 90s, as they do now. Secondly, it's the average expectancy, not lifespan. The expectancy is a statistical measurement of how long one is likely to live from the time of one's birth (or from a given age). At birth, the life expectancy would low. But if you reached maturity, the life expectancy would be quite high. In other words: The average life expectancy before the 20th century was very low. The average lifespan of mature adults was not a lot lower than today.