By Rebecca Newberger Goldstein

What would happen if the ancient Greek philosopher Plato partook in contemporary dialogues about the types of questions that he first posed, and that continue to vex us? In my view, he would have many new questions – including about our increasingly psychological approach to philosophical discussion.

Plato would probably head to a leading global technology hub: Google’s California headquarters. There, he might fall into a discussion with a software engineer about, say, whether ethical questions can be answered through crowdsourcing. He would probably love the idea of the information cloud – so abstract, so Platonic – and find Google to be the ideal tool to catch up on the vast scientific and technical advances of the last couple of millennia.

But Plato would probably be most amazed by the world’s moral progress. After all, he believed that being a “philosopher” meant assuming the responsibilities of moral reformer. Yet, though morality was always at the center of his thinking, many of the moral truths that we now take for granted never occurred to him.

For example, though Plato opposed the enslavement of Greeks, he – like every other ancient Greek – condoned the enslavement of “barbarians” (non-Greeks). Today, by contrast, even an emphatically non-philosophical person – say, Plato’s “media escort” – could easily explain why slavery is wrong: “A person is a person. Everybody’s life is just as important as anybody else’s.”

As obvious as this conclusion might seem, the world has taken millennia to reach it – and, in many ways, has yet to accept it fully. Nonetheless, we can now collectively look back at our slave-owning, wife-beating, child-brutalizing, heretic-burning, colonizing forebears and wonder how even the most profoundly moral among them failed to see that they should not behave that way. What drove this progress?

Plato held that moral progress is essentially an intellectual process, driven by reasoned arguments – a stance that many of the most influential moral philosophers, from Baruch Spinoza and Immanuel Kant to John Rawls and Peter Singer, have supported. Yet many other philosophers have rejected the autocracy of reason in humans’ moral lives, agreeing with David Hume’s assertion that “reason, in itself, is perfectly inert.” They believe that no purely abstract argument can get us to do anything that we do not want to do.

If a reasoned argument cannot move us, what can? One simple answer stands out: emotions.

Moral emotions, notably empathy, can accomplish what no bloodless ratiocination can: they make us feel – and thus want to account for – the experience of others. The more we feel, the more we care – and the more moral our motivations. In short, a stronger sense of empathy spurs moral progress.

With this shift in focus from reason to emotion, moral philosophy is increasingly giving way to moral psychology, which, by incorporating ideas from evolutionary biology, has more and more to say about human nature and our moral lives. It all comes down to natural selection.

Moral emotions like empathy are as much an outcome of the blind workings of adaptation as our upright stance and opposable thumbs – traits that are entrenched in a species through the proliferation of particular genes. We humans are most strongly empathetic toward those who share the greatest proportion of our genes: our children, our parents, our siblings, and, by lessening gradations, our extended family and tribe. Our empathy toward them might even drive us to make sacrifices that jeopardize our individual survival, but that makes perfect sense in terms of preserving our shared genes.

Of course, empathy is not the only part of our inherited nature that shapes our behavior toward others. In fact, there is also a compelling evolutionary explanation for xenophobia.

Humans evolved from primates who formed communities that worked together to survive. Given the obvious benefits of having access to more territory in which to gather and hunt, outsiders – particularly those who bear characteristics that mark them as genetically distant – were treated as foes. In this sense, the notion of “us versus them” has been fundamental to human evolution, and it continues to shape our interactions.

Just as both empathy and xenophobia can be explained by natural selection, both can be modulated by cultural factors. But do they have equal claims to being moral emotions?

Within the strict domain of moral psychology, they do. After all, a psychological telling of the story of our moral development provides no basis for encouraging us to dampen one natural inclination and nurture another.

But moral psychology does not have to tell the whole story. There is no reason why we cannot have moral psychology and moral philosophy: moral psychology to explain why moral progress is both possible and painfully slow, and moral philosophy to clarify what constitutes moral progress and to push us in the appropriate direction.

We are reasoning, deliberating human beings, and our genes are not the masters of our fate. We should not become so enthralled by the explanatory power of the behavioral sciences that we succumb to the belief that moral progress is predetermined.

Psychology tells a diminished story that leaves out our past moral advances and the hard argumentative work required to expand those advances in the future. Plato would reject this view. So should we.

Rebecca Newberger Goldstein is a philosopher and MacArthur Fellow