[M]orality is an inevitable corollary of evolutionarily useful intelligence: in becoming rational animals human beings, eo ipso, became creatures endowed with moral sense. It is important to this explanation that practical rationality be inseparable from susceptibility to moral requirements; for if it were possible to possess the one faculty without the other, then evolution could afford to dispense with morality while retaining reason. But I think that the Kantian thesis is right that rationality implies moral sense. If they are thus inseparable, then the price of eliminating morality from a species would be the elimination of (advanced) rationality from it; and, given the advantages of the latter, the price is too great.

Colin McGinn, ‘Evolution, Animals and the Basis of Morality’, Inquiry, vol. 22, no. 1 (1979), p. 93