GM: Your main argument in your book is that scientific thinking--our ability to reason abstractly, to employ experimentation and critical thinking, and to propose an outlook beyond "God said so"--has made our world significantly better. Yet the very title of your book, "The Moral Arc," comes from a phrase by a man of deep faith, Rev. Martin Luther King, Jr. So how do you see the relationship between science and religion? Are they potentially complementary, or do you think they are inherently in conflict?

MS: In fact, I open and close The Moral Arc with quotes from the Reverend Dr. Martin Luther King, Jr., one of the greatest "moral geniuses" in all history. But in his autobiography King himself said that he rejected most traditional theology and was heavily influenced by the more liberal (socially) theologians, and especially by Gandhi, who most certainly was not religious in the Western sense. In any case, the movements that both Gandhi and King led were well organized and carefully orchestrated to bring about social, political, and economic change that had more to do with the larger trends in the 20th century to end colonialism (in India in Gandhi's case) and segregation and discrimination (in America in King's case). King's rhetoric in his famous speeches was sprinkled with religious tropes and references but undergirding the movement was Enlightenment natural rights language: people should be treated equally under the law, people should never be treated as a means to an end but are an ends in and of themselves, people are born with natural rights by virtue of being human, and the like.

As I show in all rights revolutions (the abolition of slavery, civil rights, women's rights, gay rights, animal rights), religions in general and religious people in particular are late to the party in supporting social and political change like this, usually being a force for conserving the status quo. Yes, the Quakers and William Wilberforce agitated for the abolition of slavery, but the Quakers had next to no effect and it took Wilberforce decades to bring about the abolition of the slave trade in England, and in both cases their primary opponents were their fellow religious people, who argued for the justification of slavery from the Bible, from the "fact" that everyone knew blacks were an inferior race, that it was an economic necessity, that blacks were better off in slavery than they were in Africa, etc. There was no revelation from God, revealed in some new-found holy scripture, declaring "Though shalt not enslave thy fellow man for all are equal in God's eyes." And when you look at the language the abolitionists used it was grounded in rights' theory and rhetoric.

We can see how this unfolds in the current rights revolution we're undergoing right now with gay rights and same-sex marriage. It has been vehemently opposed by nearly all religions (with the exception of the more liberal religious people such as Reform Jews, Episcopalians, and Unitarians/Universalists), and led by secularists, nonbelievers, free thinkers, and the religious unaffiliated (the "nones"--those who check the survey box for "none" under religious affiliation). But this revolution will likely end legally in the U.S. this year when the Supreme Court votes on whether states can prohibit same-sex marriage, and social attitudes everywhere will then change such that by 2020 to 2025 virtually everyone will support same-sex marriage and we will look back on 2015 like we now look back on the 1950s and 1960s when interracial marriage was a lively debate. Say what? Yes, in 1959 only 4% of Americans supported the right for blacks and whites to marry. What were those people thinking?