 Suppose that the trend toward greater inclusivity with respect to the scope of moral consideration—i.e., the elimination of racial and gender barriers to the attribution of full human moral status, and the extension of substantial moral considerability to a wide range of non-human animals—counts as moral progress. One pessimistic thought that might arise here on the basis of evolutionary considerations is that human moral psychology may have evolved in such a way as to place inevitable constraints on the possibilities for achieving robust and sustained progress in these respects. While our evolved moral psychology may contain certain altruistic elements, these may be ultimately parochial, given the nature of the selection pressures faced by our Pleistocene ancestors and assuming, as most discussions do, that the long Pleistocene Epoch (roughly 2.6 million years ago to 11,700 years ago, is the one primarily relevant to the biological evolution of human psychological  traits).[11]  That is, these elements may be focused on kin and members of a perceived in-group, with other countervailing dispositions posing strong obstacles to extending that altruism to outside groups. Even if we have some capacity for autonomous moral thought, enabling at least some to grasp more inclusive moral truths, there may be such powerful evolutionary constraints built into human moral psychology that such ideas are unlikely to take hold and motivate progressive changes in a widespread and sustainable way. There may be evolutionary limits to the basic moral progress that we evolved primates can realistically hope to achieve: we may just be saddled with a largely exclusivist, tribalist morality.