Human feces are smeared all over the geological record of places people have inhabited. The chemical signature of human excrement was analyzed in sediments in a northern Norwegian lake. Starting around 2,250 years ago, the presence of people’s poo painted a picture of human population changes in the region around Lake Liland on one of the Lofoten Islands.
“Without even knowing it, early settlers were recording their history for us, and in the most unlikely of ways, in their poop,” said study author Robert D’Anjou, University of Massachusetts geosciences doctoral student. “The prehistoric settlers and their livestock pooped and their feces washed into the lake, which over time left a record of trace amounts of specific molecules that are only produced in the intestines of higher mammals. When you find these molecules at certain concentrations and in specific ratios, it provides an unmistakable indicator that people were living in the area.”
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The chemical coprostanol is produced during the digestion of cholesterol in the human gut. The chemical collects in sediments after people’s feces are flushed into bodies of water. The sediments provided evidence that from 7,300 years ago to 2,250 years ago, the region had no observable human habitation. Human and domesticated animals’ fecal signatures began showing up after that time. Two different molecular markers were also used to look for evidence of forest clearing through burning.
Population density was low in the region for much of its history, until reaching a peak in 500 A.D. A low spot in 850 suggested the area was depopulated at that time. Human presence fluctuated until dropping to another low spot in 1750.
The climatologists involved in the research note that the fecal findings reflect estimates of the Norwegian climate’s variation over time. In the harsh north, decreased summer temperatures correlated to decreased human populations.
Lake near a village on the Lofoten Islands (Florian Pépellin, Wikimedia Commons)