On May 27, 2015, as the US Supreme Court deliberated about the marriage rights of same-sex couples and the legacy of the Voting Rights Act, a New York Times interview with utilitarian bioethicist Peter Singer, famous for his philosophical work on animal liberation, asked us to consider another kind of bias: speciesism.

Speciesism, as Singer defines it, is “an attitude of bias against a being because of the species to which it “belongs” — in short, discrimination against nonhuman animals. “Humans show speciesism,” he explains, “when they give less weight to the interests of nonhuman animals than they give to the similar interests of human beings.”

Singer does not think it is speciesist to think human life is more important than that of nonhuman animals in some instances. It is only speciesist to say human life is always more important.