Varner started a research project in 2001 that looked at animals in Hare's two-level utilitarianism. The project's initial monograph, ''Personhood, Ethics, and Animal Cognition'', was released by Oxford in 2012. In the book, Varner moved away from his biocentrism, instead endorsing a developed version of Hare's ethics. Varner draws a distinction between persons, near-persons and merely sentient beings; although all are morally considerable, the lives of persons are of the most significance, and the lives of merely sentient beings are of the least. The practical consequences of this view, though initial comments were offered in ''Personhood, Ethics, and Animal Cognition'', was to be explored in ''Sustaining Animals'', with which Varner at one time had a contract with Oxford. His third book was ''Defending Biodiversity: Environmental Science and Ethics'', co-authored with Jonathan Newman and Stefan Linquist, and published with Cambridge University Press. It was published in 2017.