Motley Moose – Archive

Since 2008 – Progress Through Politics

Lies about Life Expectancy

One of my pet peeves is umpteen articles which state that in year X or civilization Y, “the average life expectancy was only 45.”

The wording of these articles leads one to believe that few people in these periods or cultures lived past 40 or 45.

This is not true. Adult humans have always lived about as long as they do now, ie. 60, 70, 80, 90, 100.

These “average life expectancy” numbers are so low because they include the number of babies who die at or just after birth (infant mortality) and the number of children who die very early in their lives (before 5). Infant and early childhood mortality was much higher in earlier centuries and millennia for all races and ethnicities than today for all types of obvious reasons. Thus, by averaging in a much higher infant and early childhood mortality rate in these periods and cultures, you end up with a much lower ‘average life expectancy.’

The fallacy here is best illustrated with turtles. Turtles have extremely high mortality rates at birth and in the days and weeks soon after birth: well over 90 percent. But those few turtles who survive these first few weeks have life expectancies of 30, 50, 100, or 150 years. As with humans, a graph of turtle life expectancy is not linear. There is a massive mortality bottleneck in the first weeks and months of life and then life expectancy skyrockets.

Unfortunately, many people read these poorly worded assertions about the average life expectancy of “early man” or ‘indigenous, non-white culture X’ and interpret these statistics to mean that up until the 1800s, very few people anywhere lived past the age of 45. That’s not true.

Adult humans have always lived about as long as they do today.

The female snapping turtle in the photo above, from Mill Brook in Westbrook, Maine just below Highland Lake, is probably 20-40 years old and will probably live (barring getting run over by a car) for another 20 or 40 or even 60 years. Nobody knows if there is even an upper limit on the age of snapping turtles, except that it is probably like humans, around 120 years.


  1. I guess life expectancy is built in somewhere above the mid 40s, where menopause sets in. I’m pretty sure we’re the only species that has evolved a ‘non fertile’ phase of menopause for females. Has something to do with the prolonged length of childhood in humans, and the need for help in child rearing.

    But the truth of it is, there are many forms of death than senescence, and humans have evolved with a life expectancy of the mid 40s, as an average. Child mortality is obviously the biggest factor, and so was disease, hunger and war. The mid 40s average also makes sense in terms of child rearing, given the fact we’re capable of reproduction in mid teens.

    Average UK Life expectancy has risen by about 10 years in the last 25 years. Could this trend continue, or even accelerate? I’ve heard it could actually go down again, mainly because of obesity and its complications (including diabetes). This threatens to be a much bigger killer than smoking.

    As for the upper limit of 120 years. I suppose this is the upper limit if heart disease and cancer are avoided. At this upper limit we begin to hit so called ‘natural aging’ – or effectively the built in obsolescence of cell apoptosis.

    If I understand this correctly, there is a limit to the number of times a cell can divide, enforced by telomeres at the end of the DNA material. This ticking self destruct mechanism has arisen because, in genetic terms, the individual life span is less important than the persistence of the DNA. Individuals are disposable in the survival mathematics of the selfish gene.

    Technically, if those telomeres could be replaced, or the ticking self destruct clock set back from time to time, there is no upper limit to human mortality.

    Is that right?  

  2. More like misconceptions about life expectancy.

    Obviously, if infant mortality is 50% and life expectancy is 45 then life expectancy for people that live past infancy is around 90. The thing is that life expectancy isn’t only rising because of improvements in infant mortality. It is also going up because people that would have died in their 60’s are now living into their 70’s and 80’s because of medical advancements. Adults now survive illnesses like pneumonia that used to kill many people. They also survive heart attacks and cancer that used to be remorseless killers. However, these differences only inch up the life expectancy, unlike improvements in infant mortality that make life expectancy numbers shoot up.

    Oh, and Chris, elephants have a type of menopause also. They usually are fertile until around 50, but can live to be 70 or older.

  3. Reducing infant and child mortality has done a great deal to skew the numbers, but more people are living longer and being more active and capable in their later years as well.  True, there have always been the elderly and the extent of that possible age hasn’t changed much, but far fewer people per capita in 1800 were over 80.

    Most of what medicine has done so far has kept people from dying before their potential time ran out.  However, medicine is only now beginning to leave the basic mechanical maintenance stage that will in the future seem a very primitive period indeed.  I forecast that medicine in the next 100 years will go through a phase much more akin to architectural engineering rather than maintenance – we will actually begin to know how to build these things, not simply how to change the tires when they wear out – and this will in fact change life expectancy fundamentally.

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