Sometime around 1150 A.D., in a small Anasazi settlement in southwest Colorado, seven people were systematically butchered and eaten by other humans, according to a recent report in the journal Nature. Such cannibalism claims are not new. Indeed, the existence of the practice is one of the most hotly debated issues in American archaeology. But unlike previous cases for people-eating, which have rested on indirect evidence, these Anasazi remains include a smoking gun--human tissue found in fossilized human feces.

Until now, the strongest evidence that prehistoric Americans of the southwest sometimes engaged in cannibalism has come from studies of bones that bear signs of cutting and roasting or boiling. Skeptics, however, argue that such marks could instead reflect other activities--certain mortuary practices, for example. (Among the strongest cannibalism critics are the descendents of the Anasazi, modern Puebloans, whose culture strictly forbids the consumption of human flesh.)

The new data, on the other hand, leave little room for doubt. Biochemical analysis of the preserved excrement revealed human myoglobin--a protein found only in heart and skeletal tissue. Other clues from the site include human blood residue on stone butchering tools, and human bones that display the same kinds of cut marks and burn marks seen on bones from animals that have been eaten. "With the presentation of the first direct evidence of cannibalism in the American Southwest in the prehistoric era," the researchers wrote in their report, "we hope that the debate will shift from the question of whether or not cannibalism occurred to questions concerning the social context, causes and consequences of these events."