This has been bothering me quite a lot, because to find out the average life-span of a society you take the death ages of all it's members, add them up and divide by the number of members. But I also read somewhere that it was only hard to get through your first few years as a baby, after that it was relatively easy to get through life because you could hunt and take care of yourself and wasn't exposed to any greater danger than when you were young and defenseless. So let's say a society has 10 members, two adults who are both above 80 and they have had 8 children that have each died before their first few years. That means that the average life-span for that particular case was below 20 years old. Is my theory true to some extend or completely nonsense??
So let's say a society has 10 members, two adults who are both above 80 and they have had 8 children that have each died before their first few years. That means that the average life-span for that particular case was below 20 years old. Is my theory true to some extend or completely nonsense??
That's correct: that's called "life expectancy at birth". Let's say your sample population lived until 80, 80, 2, 5, 3, 1, 1, 2, 3, 4: that's a total of 181 years divided by 10 people = 18 year life expectancy at birth. But, if we eliminated everyone who died before 6yo, we have only two people, who both lived until 80, so the "life expectancy at 6 years old" = 80 (i.e. everyone who made it that far, lived until 80).
Here's a recent post talking about life expectancy stats