For Lieberman's earlier study of rhesus macaques, published in 1969 in the journal Science, "We took a rhesus monkey and the started to see what the anatomical limits were," he said. The researchers made a plaster cast of a monkey throat from a macaque that died naturally. With a live but sedated monkey, the researchers manipulated the animal's tongue and documented the positions it could make. Using this information, they estimated the range of monkey speech sounds. It was much smaller than a human's, and indicated that a macaque could not produce vowels, such as the long E, common to most languages.