Though some consider the 20th century one of the bloodiest in history, psychologist Steven Pinker believes the world has become more peaceful over the course of human existence.

At a Thursday lecture entitled “The Better Angels of Our Nature: Why Violence Has Declined,” Pinker — an eminent experimental psychologist and Harvard University professor — discussed declining violence in major historical periods and the related implications about human nature. The talk marked the first event held by the Franke Program in Science and the Humanities, which was founded last year to organize interdisciplinary lectures. Pinker said he thinks society has become more peaceful because people have begun to rely increasingly on reason and empathy as a result of as a result of modernization.

“Violence of all kinds has decreased,” Pinker said. “This calls for a [rehabilitation] of the ideals of modernity and progress and is certainly a cause for gratitude for the institutions of civilizations and enlightenment that have made it possible.”

To explain his argument, Pinker laid out six periods important to the pacification process: the formation of government nearly 6,000 years ago, the development of commerce and criminal justice systems in the Middle Ages, the end of corporal punishment over the last 300 years, the post-WWII enduring peace between major world powers, the post-Cold War decline in civil conflicts and human rights movements.

He said the worldwide percentage of deaths attributable to violent acts — such as man-made famines, genocide and wars — is currently around 3 percent, but in prehistoric times, before the pacification process began, the figure was nearly 15 percent. During medieval times, he added, an Englishman was 35 times more likely to be murdered than his contemporary counterpart.

After the Middle Ages, increased communication and higher literacy rates contributed to the spread of knowledge, which Pinker said he thinks brought about a decline in corporal punishment during the period. He added that the death penalty, slavery, witch-hunts and religious persecution soon became significantly less common.

Pinker said the “frequency of Great Power wars, the duration of Great Power wars and the deadliness of Great Power wars have all declined,” though he said incidents of civil war had been increasing until the Cold War. Still, he said civil wars kill a “fraction” of the amount of people that inter-state wars kill.

When trying to pin down a specific reason for the rise of pacification, Pinker said modernity has allowed people to rely on reason, morality and empathy rather than violent urges.

“Human nature is extraordinarily complex and has always comprised both the inclinations toward violence and inclinations that counteract them — what Abraham Lincoln called ‘the better angels of our nature,’” Pinker said.

Audience members interviewed said they were impressed by the lecture.

“It was very classic Pinker — very formulaic, very simply and clearly, quantitatively laid out,” Andy Zhang ’15 said.

But other attendees doubted his argument, partially due to the complexity of data analysis.

“I imagine what I saw was a very selective presentation of data,” Sam Spaulding ’13 said, adding that Pinker has “done a good job of identifying and elucidating at least some of the factors that are responsible for the empirical drop in observed human violence.”

Pinker will appear alongside members of the Yale faculty in Friday’s panel discussion on “How Should We Address Violence?” in the Whitney Humanities Center.