Machan argued against animal rights in his widely reprinted paper "Do Animals Have Rights?" (1991) and in his book Putting Humans First: Why We Are Nature's Favorite (2004), but he also wrote on the ethics of animal treatment in his book Putting Humans First (2004).
So argumentierte er in seinem vielgelesenen Fachaufsatz „Do Animals Have Rights?“ (1991) und seinem Buch Putting Humans First: Why We Are Nature’s Favorite (2004) dafür, dass Tierrechte nicht existieren.