Compared with most animals, we humans engage in a host of behaviors that are destructive to our own kind and to ourselves. We lie, cheat and steal, carve ornamentations into our own bodies, stress out and kill ourselves, and of course kill others. Science has provided much insight into why an intelligent species seems so nasty, spiteful, self-destructive and hurtful. Inside you'll learn what researchers know about some of our most destructive behaviors.
Editor's Note: This list was first published in 2011 and was updated in March 2016 to include the latest studies and new information.
Nobody knows for sure why humans lie so much, but studies find that it's common, and that it's often tied to deep psychological factors.
"It's tied in with self-esteem," says University of Massachusetts psychologist Robert Feldman. "We find that as soon as people feel that their self-esteem is threatened, they immediately begin to lie at higher levels."
Feldman has conducted studies in which people lie frequently, with 60 percent lying at least once during a 10-minute conversation.
And lying is not easy. One study concluded that lying takes 30 percent longer than telling the truth.
Recent studies have found that people lie in workplace e-mail more than they did with old-fashioned writing.
It's a whole other matter whether people really mean to lie in many instances. Figuring that out requires coming up with a complicated definition of lying.
"Certain conditions have to be in place for a statement to rise to the level of a lie," explains philosophy professor James E. Mahon of Washington and Lee University. "First, a person must make a statement and must believe that the statement is false. Second, the person making the statement must intend for the audience to believe that the statement is true. Anything else falls outside the definition of lying that I have defended."
However, a study in 2014 found that white lies, for the right reasons, can can strengthen relationships
Animals are also known to be capable of deception, and even robots have learned to lie, in an experiment where they were rewarded or punished depending on performance in a competition with other robots.
Scroll up to click to the next item: Violence
The oldest evidence of human warfare dates back 10,000 years ago. Skeletons of 27 people show signs of projectile wounds and blunt force trauma. And so it has been ever since.
Some researchers figure we crave violence, that it's in our genes and affects reward centers in our brains. However, going back millions of years, evidence suggests our ancient human ancestors were more peace-loving than people today, though there are signs of cannibalism among the earliest pre-history humans.
A study in 2008 concluded that humans seem to crave violence just like they do sex, food, or drugs. The study, reported in the journal Psychopharmacology, found that in mice, clusters of brain cells involved in other rewards are also behind their craving for violence. The researchers think the finding applies to human brains.
"Aggression occurs among virtually all vertebrates and is necessary to get and keep important resources such as mates, territory and food," said study team member Craig Kennedy, professor of special education and pediatrics at Vanderbilt University in Tennessee. "We have found that the reward pathway in the brain becomes engaged in response to an aggressive event and that dopamine is involved."
Many researchers believe violence in humans is an evolved tendency that helped with survival.
"Aggressive behavior has evolved in species in which it increases an individual's survival or reproduction, and this depends on the specific environmental, social, reproductive, and historical circumstances of a species. Humans certainly rank among the most violent of species," says biologist David Carrier of the University of Utah.
Scroll up to click to the next item: Stealing
Theft can be motivated by need. But for kleptomaniacs, stealing can be motivated by the sheer thrill of it. One study of 43,000 people found 11 percent admitted to having shoplifted at least once.
"These are people who steal even though they can easily afford not to," says Jon E. Grant of the University of Minnesota School of Medicine.
In a study in 2009, participants either took a placebo or the drug naltrexone — known to curb addictive tendencies toward alcohol, drugs and gambling. Naltrexone blocks the effects of substances called endogenous opiates that the researchers suspect are released during stealing and which trigger the sense of pleasure in the brain.
The drug reduced the urges to steal and stealing behavior, Grant and colleagues wrote in the journal Biological Psychiatry.
Theft may be in our genes. After all, even monkeys do it. Capuchin monkeys use predator alarm calls to warn fellow monkeys to scatter and avoid threats. But some will make fake calls, and then steal food left by those that scattered.
Scroll up to click to the next item: Cheating
Few human traits are more fascinating. While most people would say honesty is a virtue, nearly one in five Americans think cheating on taxes is morally acceptable or is not a moral issue, according to a survey by the Pew Research Center. About 10 percent are equally ambivalent about cheating on a spouse.
People who espouse high moral standards are among the worst cheats, studies have shown. The worst cheaters tend to be those with high morals who also, in some twisted way, consider cheating to be an ethically justifiable behavior in certain situations.
Cheating on spouses by celebrities and politicians thought to be moral leaders has become rampant. The behavior has a simple explanation, experts say: Guys are wired to want sex, a lot, and are more likely than gals to cheat. The behavior may be particularly likely for men with power.
"People don't necessarily practice what they preach," says Lawrence Josephs, a clinical psychologist at Adelphi University in New York. "It's not clear to what extent people's ethical values are actually running what they do or don't do."
Experts say there are two main reasons people cheat on their spouses: Either they bored with their sex life or they are unhappy with their relationship. A 2015 study found that a person who is economically dependent on their spouse is more likely to cheat than those in a financially equitable relationship.
Scroll up to click to the next item: Clinging to bad habits
Perhaps everything else on this list would be far less problematic if we were not such creatures of habit. In fact, studies have found that even when the risks of a particular bad habit are well-known, people find it hard to quit.
"It's not because they haven't gotten the information that these are big risks," says Cindy Jardine of the University of Alberta. "We tend to sort of live for now and into the limited future — not the long term."
Jardine, who has studied why people cling to bad habits, cites these reasons: innate human defiance, need for social acceptance, inability to truly understand the nature of risk, individualistic view of the world and the ability to rationalize unhealthy habits, and a genetic predisposition to addiction.
People tend to justify bad habits, she says, by noting exceptions to known statistics, such as: "It hasn't hurt me yet," or, "My grandmother smoked all her life and lived to be 90."
Scroll up to click to the next item: Bullying
Studies have found that half or more of grade-school children experience bullying. A European study found that children who bully at school are likely to also bully their siblings at home. That led a researcher involved in the study to speculate that bullying behavior often starts at home.
"It is not possible to tell from our study which behavior comes first, but it is likely that if children behave in a certain way at home, bullying a sibling for instance, if this behavior goes unchecked they may take this behavior into school," said Ersilia Menesini of the Universita’ degli Studi di Firenze, Italy.
But bullying is not just child's play. One study found that almost 30 percent of U.S. office workers experience bullying by bosses or coworkers, from withholding of information critical to getting the job done to insulting rumors and other purposeful humiliation. And once it starts, it tends to get worse.
"Bullying, by definition, is escalatory. This is one of the reasons it’s so difficult to prevent it, because it usually starts in really small ways,” says Sarah Tracy, director of the Project for Wellness and Work-Life at Arizona State University.
Experts say to combat workplace bullies, respond rationally, specifically, and consistently.
Why do we do it? To gain status and power, psychologists say. And for some, it may be hard to resist the behavior. Researchers have seen bullying behavior in monkeys and speculate that the behavior may stretch way back in our evolutionary tree.
Scroll up to click to the next item: Nipping, tucking and plumping
Americans spent a record $13.5 billion on surgical and nonsurgical "aesthetic procedures" in 2014, the latest year for which data is available. Some 17 percent of U.S. residents now get cosmetic procedures, the industry estimates. Some would call it self-edification, of course, or art, or a way to kill time or perhaps rebel against authority. But in general, and given that people have died from cosmetic surgery procedures, what makes so many people so intent on artificially remaking themselves?
First, it's worth noting that while options at the body shop have never been more varied, the practice is ancient, often tied to cults and religions or power and status, and in fact much of the modern nip, tuck, paint, poke and plump procedures are benign compared with some ancient practices. People have reshaped their heads, elongated their necks, stretched their ears and lips, painted their bodies or affixed permanent jewelry for thousands of years.
Perhaps the strongest motivations nowadays are to be beautiful, however one might define that, or simply to fit in with a particular group.
The lure of beauty can't be denied as a prime motivator to nip and tuck. Studies have shown that shoppers buy more from attractive salespeople; attractive people capture our attention more quickly than others; and skinny people have an easier time getting hired and promoted.
"There's this idea that if you look better you'll be happier. You'll feel better about yourself," says psychologist Diana Zuckerman, president of the National Research Center for Women & Families. "And logically that makes so much sense, because we live in a society where people do care what you look like."
A sign of the times, as Baby Boomer age: While cosmetic surgery sales sagged during the Great Recession a few years back, wrinkle-blasting laser treatments skyrocketed. In 2015, the industry said cosmetic procedures for men were up 43 percent over the past 5 years.
Scroll up to click to the next item: Stress!
Stress can be deadly, raising the risk for heart problems and even cancer. Stress can lead to depression, which can lead to suicide — yet another destructive behavior that's uniquely human (and glaringly not on this list).
But exactly why we stress is difficult to pin down. These truths will resonate with many, however: The modern workplace is a source of significant stress for many people, as are children.
More than 600 million people around the world put in 48-hour-plus workweeks, according to the International Labor Organization. And advances in technology — smartphones and broadband Internet — mean a blurring of the lines between work and free time. About half of Americans bring work home, according to a recent study.
The stress of being a parent while also working is borne out by a 2007 study that found older people feel less stress. However, research in 2015 found high-stress jobs raise the risk of stroke, and stress can increase the risk of memory problems in older people.
"Many older workers are empty-nesters," says researcher Gwenith Fisher, an organizational psychologist at the University of Michigan's Institute for Social Research (ISR). "They don't have the same work-personal conflicts that younger and middle-aged workers deal with, juggling responsibilities to children along with their jobs and their personal needs."
Health experts suggest exercise and adequate sleep are two of the best ways to battle stress. [More Tips]
Scroll up to click to the next item: Gambling
Gambling, too, seems to be in our genes and hard-wired into our brains, which might explain why such a potentially ruinous behavior is so common.
Even monkeys gamble. A study that measured monkeys' desire to gamble for juice rewards found that even as potential rewards diminished, the primates acted irrationally and gambled for the chance to get a wee bit more.
A study published in the journal Neuron last year found that almost winning activates win-related circuitry within the brain and enhances the motivation to gamble. "Gamblers often interpret near-misses as special events, which encourage them to continue to gamble," said Luke Clark of the University of Cambridge. "Our findings show that the brain responds to near-misses as if a win has been delivered, even though the result is technically a loss."
Other studies have also shown that losing causes gamblers to get carried away. When people plan in advance how much to gamble, they're coldly rational, a study last year found. But if they lose, rationality goes out the window, and they change the game plan and bet even more.
Scroll up to click to the last item: Gossiping
Gossiping is a social skill, not a character flaw, argues psychology researcher Frank T. McAndrew at Knox College in a 2016 op-ed article.
We humans are evolutionarily set up to judge and talk about others, no matter how hurtful it might be, researchers say. Here's how Oxford primatologist Robin Dunbar sees it: Baboons groom each other to keep social ties strong. But we humans are more evolved, so we use gossip as social glue. Both are learned behaviors.
Gossip establishes group boundaries and boosts self-esteem, studies have found.
In many instances, the goal of gossip is not truth or accuracy. What matters is the bond that gossiping can forge, often at the expense of a third party.
People are mostly likely to spread a story if it's about someone familiar to them, and if the story is particularly "juicy," according to a 2014 study. "When two people share a dislike of another person, it [gossip] brings them closer," says Jennifer Bosson, a professor of psychology at the University of South Florida.