It’s said that love makes the world go ’round, although the same might be said of revenge. Getting even is a human urge that seems nearly as basic. When your brother slugged you on the playground, you slugged him back without a second thought. When your so-called best friend tweeted that embarrassing photo of you to everyone in school, there had to be some retaliation.

It’s hard to imagine a world without revenge. No Hamlet. No Dirty Harry. No Tonya Harding. No road rage. No fighting in hockey. No schoolyard shootings to atone for all the bullying you’ve endured. No Hatfields and McCoys, or Crips and Bloods, or Israelis and Palestinians. No 9/11. No hunt for Osama bin Laden.

Even science concurs that revenge can feel sweet. Plotting to get even causes a rush of neural activity in the caudate nucleus, a part of the brain associated with pleasure. But it’s plain, too, that cycles of revenge lie at the heart of the world’s most intractable problems. We love revenge, and it’s killing us.

The idea of payback goes way back. The Bible barely gets going before Cain murders Abel. Ancient tribes found ways to institutionalize revenge. The code of “an eye for an eye” offered a civilizing rationale for proportional retribution, although in “honor societies” proportionality often got out of hand.

A mere insult was reason enough for demanding satisfaction, and satisfaction could lead to death. In 1804, the vice president of the United States, Aaron Burr, killed the former secretary of the treasury, Alexander Hamilton, in a pistol duel after Hamilton wrote nasty things about him in a newspaper. It was Hamilton’s 11th duel.

Today, revenge killings retain their popularity. Earlier this month, the United Nations reported that 6 million people had died from personal violence between 2000 and 2012, more than in all wars combined. It’s safe to assume that revenge played a major role.

Revenge remains a clear motive, too, in the state-sanctioned executions of convicted murderers. There have been 796 such deaths in the United States since 2000, with a strong majority of the public (2 to 1) favoring them. Nearly 4,000 years after the notion was first uttered in Babylon, an “eye for an eye” still prevails.

Christmas brings something of a counterpoint to all of that. The baby in Bethlehem, so celebrated tonight by the world’s 2.4 billion Christians and acknowledged by millions of others, grew up to become an itinerant preacher and miracle worker with remarkably radical views, among them a rejection of the eye-for-an-eye code that seems so embedded in human nature. Instead of getting even, Jesus of Nazareth urged his followers to love their enemies and, if struck on one cheek, to offer the other as well.

But using humility to break the cycle of revenge has proved difficult for the secular and for the religious of all faiths. Yes, the end of apartheid in South Africa was marked by forgiveness, not vengeance. The reunification of Germany failed to incite vendettas against the hated East German secret police. And Indianapolis Colts quarterback Andrew Luck, rather than trash-talking his opponents, likes to compliment them, especially after absorbing a big hit. But those are exceptions to the harsher reality.

Some prefer to qualify Jesus’ words — and similar utterances by others — as being against “personal” revenge only. Corporate revenge from, say, God or fate or government is OK, they say, especially if it’s cloaked in the language of justice.

Much has been written about the differences between the two — that revenge is emotional, personal, vindictive and retaliatory, for example, while justice is rational and impersonal and seeks closure and balance. But the line of separation seems thin and changeable from culture to culture. The public beheading of an aid worker apparently passes for justice in some quarters.

Indeed, modernity seems to frustrate the eye-for-an-eye dictum. Revenge may have been “purer” and more direct in ancient times, critics say, when the offender’s identity was easier to know. But who nowadays is to blame for racism? Or the financial meltdown of 2008? Or the way that Western culture defiles the Islamic ideal?

Literature, it’s sometimes said, offers a cathartic alternative to revenge. We feel good following the avenger on his way to settle the score without having actually to seek revenge ourselves. Maybe that’s why revenge is so pervasive in works of fiction.

Still, revenge may not be all that it’s cracked up to be. Newer research on the brain suggests that the sensual “pleasure” of vengeance often disappoints in the end. By obsessing about getting even, avengers expect to feel better and gain closure, but eventually they feel worse than those who just let it pass. Psychologist Kevin Carlsmith of Colgate University said it this way in an article published just before his death: “Those who don’t have a chance to take revenge are forced, in a sense, to move on and focus on something different — and they feel happier.”

In other words, revenge gets its comeuppance in the end. Maybe that’s a Christmas message to hold onto.