Douglas Maclean agreed that Singer raised important questions and challenges, particularly with his argument from marginal cases. However, Maclean questioned if different species can be fitted with human morality, observing that animals were generally held exempt from morality; Maclean notes that most people would try to stop a man kidnapping and killing a woman but would regard a hawk capturing and killing a marmot with awe and criticise anyone who tried to intervene. Maclean thus suggests that morality only makes sense under human relations, with the further one gets from it the less it can be applied.