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Why we do stupid stuff
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.
We lieSlide 2 of 21
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: ViolenceSlide 3 of 21
We crave violenceSlide 4 of 21
We crave 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: StealingSlide 5 of 21
We stealSlide 6 of 21
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: CheatingSlide 7 of 21
We cheatSlide 8 of 21