This inaugural lecture by Sarah Coakley, delivered at the University of Cambridge on 13th October 2009, considers the striking cultural dominance, in the latter part of the twentieth century, of a violent and negative rendition of the notion of sacrifice. Coakley asks whether it is a coincidence that at the same time, philosophers of religion have tended to be in notable retreat from bold public claims about the rationality of Christian truth. In contrast to this double trend, and in riposte to the 'New Atheism' of the secularists, Coakley argues that the most recent deliveries from evolutionary biology augur a vision of sacrifice which is both rationally defensible and biologically grounded. Evolutionary dynamics, religious practice and hermeneutics, and new arguments for the rationality of belief belong together; and this nexus of themes demands the closest attention as the world confronts the profoundest ecological crisis it has yet known.