Civilization owes much to corn, and to the early people who first cultivated it. Researchers led by Anthony Ranere, professor of anthropology at Temple, and Dolores Piperno of the Smithsonian Institution's National Museum of Natural History excavated caves and rock shelters in the region, searching for tools used by their inhabitants, maize starch grains and other microscopic evidence of maize. In Mexico's Xihuatoxtla shelter, they discovered an array of stone milling tools with maize residue on them. The oldest tools were found in a layer of deposits that were 8,700 years old. This is the earliest physical evidence of maize use obtained to date, and it coincides very nicely with the time frame of maize domestication estimated from DNA analysis.