If there has been progress in ethics recently it has been through the realization of some ethicists that animal happiness and suffering has to be considered equally with that of human beings. I should draw attention here to the remarkable book Animal Liberation by Professor Peter Singer of Monash University. Christian ethics has been deficient in this respect, since animals have been regarded as things made by God for the use of men. However, utilitarianism has been mindful of animals. Unlike Kantians, who are primarily concerned with the rationality of those with whom we deal, Bentham, for example, was clear that the important question was not whether animals were rational, but was whether they can suffer. At any rate, the increased attention to the sufferings of animals is one of the most notable examples of progress in ethics over the last hundred years or so. We should, of course, be equally mindful of extra-terrestrial consciousnesses, should we come across any such and have to interact with them.
(J. J. C. Smart, "Ethics and Science," Philosophy 56 [October 1981]: 449-65, at 450 [footnotes omitted])