Cita APA (7a ed.)

Singer, P. (2011). The Expanding Circle: Ethics, Evolution, and Moral Progress (1st Princeton University Press pbk ed.). Princeton University Press.

Cita Chicago Style (17a ed.)

Singer, Peter. The Expanding Circle: Ethics, Evolution, and Moral Progress. 1st Princeton University Press pbk ed. Princeton, NJ: Princeton University Press, 2011.

Cita MLA (8a ed.)

Singer, Peter. The Expanding Circle: Ethics, Evolution, and Moral Progress. 1st Princeton University Press pbk ed. Princeton University Press, 2011.