"...mein Acker ist die Zeit", Aufsätze zur Umweltgeschichte - Oapen

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the decrease of life expectancy of people in Europe between 500 and 1350 CE.
Data were employed from calculations of life expectancies from skeletal series
coming from France to Poland and from Scandinavia to Switzerland (no Mediterranean
series included). Within these 800 years, life expectancy at birth was reduced
from an average of 33 years to an average of 22 years. 733 Of course there are methodological
obstacles in calculating these values, furthermore the data may have less
reliability with respect to the unknown number of children in burying places and
graveyards etc. However, not the exact number of years for life expectancy at birth
is decisive, it is the order of magnitude that is important. Whatever the basis of
calculation is: life expectancy is reduced by a considerable number of years.
Obviously this is in accordance to textbook knowledge in ecology about the
negative correlation of life expectancy and population density for many mammals
and other animal species, sometimes even plants, suggesting this negative correlation
being a basic biological principle. Human life expectancy became positively correlated
with population density (in Western societies) with the start of the demographic
transition in the 18 th century, supported by inventions of health care, sanitation
and hygiene and a perpetuation of food supply from the 19 th century on. But
all this will happen only 500 years after the Black Death, and thus it seems as if
pure biology explains the decrease for pre-Black Death times satisfactorily.
But “density” is not a sound parameter. Taking 1800 CE as a reference before
the population transition really became established, population density in central
18th century Europe is likely threefold of that of 1300. But life expectancy at birth
in 1800 was approximately of the same dimension as it was in 500 CE: about 30 –
35 years. The question is: what added to decreasing life expectancy at birth during
the High Middle Ages prior to the Black Death, bringing it down to some 20
years?
Now is the time to remember the famous agrarian historian Ester Boserup.
She coined the term “agricultural intensification”: Changes often induce agricultural
innovation but increased labour cost (Grenzertragsnutzen). The higher the
population density the more hours the farmer must work for the amount of produce.
Therefore workloads tend to rise while efficiency drops: Raising production
at the cost of more work at lower efficiency.
Surely, the period of 500 to 1350 CE was a period of changes, changes in
power, in climate and in agrarian technology, thus bringing all prerequisites together
and unravel the situation. Basically it was and remained a rural society, depending
on its yields. The population grew by an increased total of yield (only).
Feeding a population at the edge of the carrying capacity would necessarily mean
increased labour costs for the peasants. This would mean exhaustion, since productivity
could only be raised by intensified labour and extension of arable plots.
733 A table of life expectancies at birth for Central European skeletal series can be found in
B.Herrmann (1987) Anthropologische Zugänge zu Bevölkerung und Bevölkerungsentwicklung im
Mittelalter. In: Herrmann B, Sprandel R (eds.) Determinanten der Bevölkerungsentwicklung im
Mittelalter. Acta Humaniora VCH; Weinheim. p. 55-72