KUJAWY, POLAND—Science in Poland reports that high nitrogen levels detected in the isotopic analysis of human and animal bone collagen recovered from more than 30 archaeological sites in northern Poland indicate that Neolithic farmers fertilized their fields. The study also showed that these early farmers ate little fish and other freshwater foods. Then, between around 2800 and 2200 B.C., populations such as the people of the Corded Ware culture from an area near the Danube River arrived in what is now northern Poland, said Łukasz Pospieszny of the University of Gdańsk. The newcomers adapted to local conditions, he explained, but they maintained their own dietary patterns based on meat and dairy...