R. Douglas Fields, a very calm government scientist in his 50s, was emerging from a Barcelona metro stop with his daughter when a man tried to rob him.

The next thing Fields knew, he had the guy in a choke hold on the ground.

"Now I'm on the ground in a street fight, realizing that this signal never went to my cerebral cortex. There was no consciousness involved," Fields, a neurobiologist at the National Institute of Child Health and Human Development, said at a talk at New York University on April 20. "And then I realized that if there's something in your environment that can cause you to engage in violence, risk your life and limb, in an instant ... I wanted to understand how that worked."

He was so intrigued by this uncharacteristic display of rage that Fields decided to research what made him — and so many others found in news stories every day — snap. This inquiry turned into his latest book, "Why We Snap: Understanding the Rage Circuit in Your Brain."

In it, Fields has gathered what he calls the "nine triggers of rage." He has based most of the book on interviews and case studies of particular incidents of violence or heroism, but Fields also cites various neurological and behavioral studies throughout.

"If you learn to recognize these triggers," he writes, "you can understand why a person snapped in a specific situation." Here's what the triggers are — though bear in mind these are not justifications for inevitable violence, simply the things that frequently spark it.

1. Life-or-death situation

This one makes sense biologically. If your life is in danger, you're probably going to react rashly, possibly in anger.

"Almost anyone, and most animals," Fields writes in the book, "will defend themselves in what is perceived as a life-or-death attack."

If you're about to die, fighting back may be your only option.

2. Insult

Triumph the Insult Comic Dog may provoke some rage.

Men used to duel to the death over insults.

"Verbal insults are the human equivalent of head-butting — a means of challenge and establishing dominance," Fields writes in the book.

Animals fight; we sling mean words. Both can provoke an angry response.

3. Family

Liam Neeson's character in the Taken movies was protecting his family, violently.

Like a mama bear protecting her cub, humans are also wired to guard our own family.

It's part of how our species has survived.

"Evolutionary success is determined by passing on an individual's genes to the next generation," Fields writes. "Protecting offspring, and even siblings and parents who closely share your genes, increases the odds that your genes will be passed on."

4. Environment

Humans are so territorial that in some states it's even legal to shoot someone who broke into your home.

"Most animals will protect their own environment, their territory and home," Fields writes. "The reasons are clear: home and territory provide the basic necessity for survival."

5. Mate

The 2009 Beyonce movie, "Obsessed," was a prime example of a jealous lover reacting with rage.

People can become enraged both when they are trying to win — and trying to keep — a mate.

"Violence between males and females frequently occurs within intimate sexual relationships," Fields writes. "This is the trigger for violence in domestic disputes, infidelity, and attacks by jealous lovers."

6. Social order

Road rage has several triggers, one of which is "order in society."

If people feel their social status is threatened, they can get very angry.

This trigger can be responsible for incidents ranging from road rage to peaceful protests that erupt into violence.

"Rage attacks frequently break out in response to a perceived social injustice," Fields writes. "This trigger often incites mob violence."

7. Resources

If you're being robbed, like Fields was in Barcelona, your instinct may be to fight back.

This is because you are trying to protect your resources, just as animals do in the wild with food.

"In human society, money and other forms of valuable property are equivalent to food," Fields writes, "because these valuables can be transformed into food, housing, and territory."

8. Tribe

Law enforcement officials inspect an arrested individual's tattoos for signs of gang affiliation in Houston, Texas on March 8, 2016.

Humans are highly social creatures, so if we feel that our tribe or group is threatened, we can react in rage.

People build moats, walls, and go to war over tribal altercations.

"These same triggers of violence we see popping up again and again as the cause for wars, the cause for riots, the cause for violence breaking out at political campaigns, and political rallies — that's tribalism," Fields said at the NYU talk.

9. Stopped

"Animals will struggle violently to escape restraint, even to the extent of gnawing off their paw if caught in a trap," Fields writes. "Humans are no different."

We want to be free. One side of this reaction is exemplified by Aron Ralston cutting his own arm off when he got trapped under a rock (as depicted in the movie, "127 Hours").

But this trigger can also be responsible for revolutions, war, and massacres.

"Any one or more of these [nine] triggers can initiate an automatic rage response," Fields writes in his book. "Whether it does or doesn't depends on additional factors specific to the situation, the individual's state of mind, and other contributing stresses and influences."

Culled from Business Insider