 He joined the faculty at the University of California, Irvine in 1990.Working with Laurence D. Mueller, Graves found that population density is an important factor in determining both the immediate chances of survival and the course of natural selection for small organisms such as fruit flies.In "Chance, Development, and Aging", "Human Biology" December 2001, Graves wrote that the explanation of individual patterns of aging must take into account subtle mechanisms such as extensive chance variations in cell number and connections, in cell fates during differentiation, and in physiological patterns that arise during development.