Monday, 20 February 2012

The 35 year lifespan myth

Why couldn't they just say '70'?
What is the human lifespan? We still tend to hold on to a magic number from the Bible – “three score years and ten” or seventy years as an idea of the natural length of life, but what has human life expectancy really been like through history?

Average life expectancy has grown phenomenally in the last hundred years. From the dawn of history through to the nineteenth century, average life expectancy has been between 25 and 35. Now it is in the high 60s, and higher still outside Third World countries.

How, then, did the writers of the Bible come up with the over-inflated but visionary figure of 70? This is because average figures can be very misleading. The historical figures are dragged down by a very high infant mortality rate. Before modern medicine, most children would not make it to adulthood. Similarly, many women died while giving birth, in their twenties or younger. If early deaths are excluded from the average, lifespans in the 50s, 60s and 70s were not uncommon.

Typical lifespans of those who survived into adulthood dropped as we moved from the pre-industrial to the early industrial age, though more children were surviving, so this isn’t clearly reflected in the averages. Then lifespans started to rise as modern medicine kicked in, up to the current impressive high. Now, childhood mortality is at an all time low. As Armand Leroi points out (in his book Mutants), 1994 was a remarkable year in this respect. In 1994, no eight-year-old girls died in Sweden – not a single one. While this was just one point in the statistics – the next year, no doubt a handful did – it is still a notable fact that would have been inconceivable to our medieval ancestors.

When there’s a funeral for a baby or a child it is always a very emotional and particularly sad occasion – it’s sobering to think that not many years ago, and throughout all of history before that, the majority of funerals were for babies and children.

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