Pheromones and Mammals: "Humans are 'the hardest of all' mammals to work with, Singer says. Yet some studies suggest that humans may also respond to some chemical signals from other people. In 1971, Martha McClintock, a researcher who is now at the University of Chicago (she was then at Harvard University), noted that college women who lived in the same dormitory and spent a lot of time together gradually developed closer menstrual cycles. Though the women's cycles were randomly scattered when they arrived, after a while their timing became more synchronized."