We like to think that reason is the supreme adaptation; that rational animals deserve preferential treatment; and that nonhumans, because they don't have reason, have no intrinsic moral value. However, after Darwin, this is no different and no more convincing than, say, an elephant thinking that trunks are the supreme adaptation; that animals with trunks deserve preferential treatment; and that non-elephants, because they don't have trunks, have no intrinsic moral value.

(pp. 263-264) - Darwin, God and the Meaning of Life: How Evolutionary Theory Undermines Everything You Think You Know (2010)