Richard Field on Management and Information Science

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The generalization is often stated that life expectancy in earlier times was short. The quotation from Thomas Hobbes in Leviathan to describe pre-modern times is used in many cases to describe life then as "nasty, brutish, and short". And yet I can't believe these statements. To hear that life expectancy in the middle ages was 35 years, or 30, just makes no sense to me. Investigation has shown that life expectancy is the mean age at death. So for all the people of an area and time the average age at which they died is calculated. Because of heavy infant mortality both at birth, in the first year of life, and in the first five years of childhood, the averages are driven down. To me it makes more sense to ask what was the age distribution of a population at stable state? If there are 1000 individuals alive at a given time, how many are infants, how many young adults, and so on. If a population is suffering high infant mortality over a fifty year period there may be many births and deaths of children in that period, yet they form only a small percent of the total number of individuals living at any one time. There is, or was, turnover in the population of the young.

What I would like to see is tables that illustrate stable state age distributions for different societies at different times. Then it would be possible to think of what it might have been like to live in such societies. How many old people were there, say over 60 years old? Were there a very few or a significant number?

The book Expectations of Life by H.O. Lancaster (1990) gives one suggestive table on page 8. A restatement of the table follows. Note in the far column that what is given is the number of years a member of the aristocracy of England could expect to live, given that he had reached the age of 21.

Time Period Number of Males Observed Further years of life expected at age 21 1200-1300 7 43.14 1300-1400 9 24.44* 1400-1500 23 48.11 1500-1550 52 50.27 1550-1600 100 47.25 1600-1650 192 42.95 1650-1700 346 41.40 1700-1745 812 43.13 *black death

From the table it is clear that even in the middle ages, if the person could get through childhood and early adulthood, he could expect to live to 64 or so. That means that there were older people living in the society. Though the data comes from the aristocracy, it is argued that it applies more generally in the society. While the aristocracy are less affected by famines due to their wealth, they are more susceptible to death from serving in the military.

Lancaster's book says that there isn't much evidence of age at death for prehistoric societies. But we hear of life expectancies of early man of 25 to 30 years. What was likely done is authors have taken modern data on life expectancies, which are on an upward trend with no end in sight, and extrapolated backwards. But modern societies have largely gained increasing life expectancies by sharply limiting mortality among the young. So my guess is that if you got in a time machine and went into early populations you would find lots of older people. It simply wasn't unusual to live to 70 or more. So don't think about so-called 'life expectancies' of 25 years for people in some early society and think they barely had time to procreate before they died. It just wasn't so.

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