D'Anjou, a paleoclimatologist, was analyzing drilled-out samples of sediment years ago when he found distinctive chemicals called human fecal sterols. Sterols are produced in the gut of mammals as they digest cholesterol in their food. Each mammal produces a different type of sterol, and since wherever humans go, they poop, the presence of human sterols means that humans were inhabiting the area.
Raw Story wrote to D'Anjou and asked whether human fecal sterol studies have been done on U.S. lakes to determine this continent's pattern of human habitation.
"I mean, the specific approach we took in this study, using biomarkers (molecules produced by (at one time) living organisms which have been preserved in sedimentary archives ) to track environmental changes due to both natural variations in the climate as well as human impact has surely been applied to numerous lakes in the U.S. by countless studies," he replied, "However, in these studies and in common biomarker records, the signal of human activity is often similar to that which might arise from changes in climate. On the other hand, fecal sterol biomarkers indicative of the presence of humans and grazing animals, and the products of biomass burning" can provide "direct and unambiguous indicators of human activity that enable human impacts on the landscape to be distinguished from the effects of climate change."
In other words, previous research techniques, including the analysis of coprolites (fossilized human dung), have only been able to yield "snapshots" of data, providing merely a definitive yes or no as to whether or not people ever set foot on the spot. Examination of the layers in lake sediment, said D'Anjou, can "allow us to reconstruct the continuous history of settlement in the area and when bolstered by other records of changes in the landscape or practices associated with human settlements (animal husbandry and land-clearance practices) we can begin to build a more complete story of when and where humans were through pre-history and how they began to shape the natural landscape into what we see today."
For a study like the one conducted at Lake Liland to take place in the U.S., D'Anjou said that a site would have to be found that meets a number of requirements, "There needs to be a lake with a continuous dateable sedimentary record going back throughout the Holocene period, that has good preservation of organic material. Second, there needed to have been a population of early human settlers living in and around the lake catchment."
He wrote, "If such sites can be identified, the opportunities are endless, and the results from such studies could greatly help our understanding of the peopling of the Americas as well as paleoenvironmental changes that have occurred over the most recent several thousand years."
In the past, paleoclimatologists have attempted to track human migration by analyzing certain species of pollen associated with crop domestication or charcoal from ancient fires. Unfortunately, pollens can be carried for miles by wind and fires occur in nature regardless of human interference, so the new method, which D'Anjou and his team presented this week in the Proceedings of the National Academy of Sciences, is believed to be the most accurate available.
Regular archaeologists have used sterols to track patters of human habitation and agriculture on land and modern environmental scientists use them to spot sewage leaks and contamination in streams and estuaries, but D'Anjou was the first to look for sterols in lake sediment. He has been able to square his results at Lake Liland with what historians know of human activity in the area, as well as with data collected from other sources of climate history like tree rings.
According to Time, "For the first 4,000 or so years of the record, human fecal sterol levels were nearly zero, and the levels of the hydrocarbons were low too. The plant waxes suggest that the land was forested. Then, about 2,250 years ago, the sterol and hydrocarbon levels spike dramatically, and a greater proportion of the land was cleared. The levels of fecal sterols remain elevated for hundreds of years, often falling after a sudden temperature drop, which might have made agriculture untenable in the already-chilly Arctic. Sterol levels rise again when the temperature warms, but a significant dip occurs around 550 AD, continuing gradually downward, in tandem with records of migrations in Scandinavia, mostly for political and socioeconomic reasons. Levels later recover, but another dip occurs around the time of the Black Plague in the 14th century, when historical records show that more than 80% of the area’s farms were abandoned."
Ted Van Vleet, an emeritus professor of chemical oceanography at University of Southern Florida who uses sterols to track sewage dumping in seawater said, "There are maybe other interpretations, but the scenarios that the authors present [are] solid.”
D'Anjou's team, however, conceded that drops in the level of sterols only point to a corresponding drop in population. Climatologist Ray Bradley, D'Anjou's advisor, said, "If it got a lot wetter, and there was more transfer of material from wherever they were pooping, that kind of uncertainty is definitely there.”
Although, he said, the sterol tests are proving to be highly accurate and very sensitive, meaning the likelihood of a major error is exceedingly small.
Team member David Finkelstein, meanwhile, is carrying out research closer to home. He is studying the different ways that fresh poop and aged poop appear in the chemical record. Frequently he makes calls to local farmers in search of manure for study. Sometimes, his queries are met with skepticism.
“’Are you guys serious?’ That’s always the question on the other end of the phone,” he told Time, two which he replied, "'Yes, sir, we are serious about our poop here.’”
[image of Rob D'Anjou via University of Massachusetts official website]
