Such data can't rule out the possibility that the trophy heads were acquired in fights between local Nasca groups, remarks William Isbell of Binghamton University in New York.
Nasca culture existed in the coastal lowlands of what is now southern Peru from about 2,000 to 1,250 years ago.
Much archaeological evidence suggests that local Nasca groups sometimes engaged in battles and raids among themselves, in line with Knudson's finding, comments Kevin Vaughn of Purdue University in West Lafayette, Ind.
Nasca sites of various ages have yielded more than 150 trophy heads, often found in graves as offerings to the dead and in public buildings.
Biochemical profiles of tiny amounts of tooth enamel taken from these trophy heads were compared with corresponding data for 13 intact Nascaskeletons already excavated from any of three Nasca cemeteries.
It's thus likely that individuals from both groups lived in the Nasca region, Knudson says.