Sometimes increases in longevity are pointed to as a reason to believe that things are getting better – so, how robust is this reasoning?
Imagine two rectangles, one with a width of 90 and one with a width of 100. Which rectangle has a greater area? The answer is: you don’t know, unless you make assumptions about the height of the rectangles. We can think of width being longevity and height being average quality, and the area being total value. Therefore, saying that one society has higher longevity rates than another is to say little about which society has more value, unless you make assumptions about average quality. More pithily, longevity in itself is an empty vessel.
In a simple utilitarian calculus, the relevant question is: how good is the person’s life over that time? Increases in longevity could conceal that things are getting worse, so measured, in two specific ways:
a) It is possible that the marginal increases in people’s longevity at some point involve less quality, and
b) It is possible that degradations in the quality of people’s lives on the whole are occurring, in such a way that there is a net decrease in the sum of quality despite increases in longevity.
So increases in longevity, alone, not only don’t show that things are linearly getting better relative to the increase in longevity, but they don’t even show that things are getting better in general in one’s society. The question then is whether one has reason to believe that things are getting worse either marginally or in general in terms of quality.