We all know that one cannot make a doppelganger, or find one in an alternate universe, without that doppelganger being evil. But how is that great capacity for malice instilled in a twin? We asked biologist Terry Johnson, author of How to Defeat Your Own Clone, how to construct an evil twin using science.

To begin with, we have the disclaimer. As everyone knows, there is no absolute physical characteristic that will produce an 'evil' person. The best way to get someone to act like a horrible human being is to be a horrible human being to them, especially for prolonged periods of time. However, since we are a science fiction website, and not a catalog of the incredibly sad things that portions of humanity do to other portions of humanity, we'll at least attempt to take a look at the best way to scientifically engineer an evil person.

The Genes of Evil


Although genetics are put forward as all-powerful in this day and age, they are, according to Johnson, the least likely way to build an evil twin. He says, in no uncertain terms, "Genetic tweaking is right out. While there are gene correlations with behavioral problems, there are none so strong that would "build an evil twin". At best, they would "build a twin with a slightly higher predisposition to a specific bad behavior, which comes along with many other predispositions - good, bad, and neutral - that are unknown. Lots of genes have been put forward as correlating to bad behavior, but none that have ever even been sold as causative, let alone proven."

And it looks like all available studies support that. Some time ago there was a great deal of fuss made about men with an extra Y chromosome, due to an initial study at a state hospital. An unusually high percentage of the male patients were XYY. This correlated to a bit of extra height, but researchers wondered, in an initial paper, if perhaps the patients were in the hospital due to anti-social behavior. Any link was disproved later, but people took notice, and a mistaken public perception spread.


The closest thing to a genetic predisposition to aggression and violence happens in genes that control, in some way, the neurotransmitters in the brain that relate to emotional stability. The most definitive study on humans was done in New Zealand. A group of children were studied from birth to adulthood. Out of the group, 442 boys were studied and tested for a gene that controlled the production of monoamine oxidase A. This gene was on the X chromosome, and so harder to study in girls, since they can have two different versions. The enzyme breaks down neurotransmitters that regulated mood - like serotonin. One version of MAOA gene produced very little of the enzyme. The boys who had that gene were more likely to lie, steal, fight, or bully, but only if they had been abused as children. Of this subset of a subset of a group of kids, 85 percent percent continued criminal activity into adulthood. Still, it took social, and not only genetic factors, to influence the kids.

Other tests do show correlations between genes that mess with the emotional part of the brain and aggressive behavior, but they are not as extensive. A test of 500 women, much smaller in scope than the New Zealand test and done at the University of Pittsburgh, found that women who had a gene that inhibited reception of serotonin scored higher on basic tests for anger and aggression than women who did not have the gene.

The best evidence for genetics alone causing aggression and violence comes from a test done at Johns Hopkins on specially-bred mice. The mice were engineered so that they would lack a gene that controls the production of nitric oxide. This is a neurotransmitter that is found in pathways in the brain that regulate emotional behavior. The mice were both hypersexual and extremely aggressive. Researchers noted that the mice would also be bold in situations that other mice would find intimidating, and concluded that the specially-bred mice lacked inhibitions and fear responses that other mice had. The mice would often fight each other, sometimes to the death. However, the missing gene came with other physiological abnormalities, and so the researchers were unable to conclude absolutely that it was the lack of nitric oxide that caused the aggression, and not some other modification.

Aggressive Hormones

Could one make an evil twin with hormones? They are a little more likely than genetics. After all, the brain specifically cooks us up a cocktail of them when we believe that we need to fight. But, when we look at the data out there, the results are confusing. Testosterone is generally what leaps to mind when people think of aggression, and both men and women have it - though generally in differing amounts. Studies on what exactly it does to people differ. Researchers in India thought that there might be a correlation between sensitivity to testosterone and criminal behavior. They found that violent criminals had a particular sensitivity to the stuff. However, a research team from the University of Alberta found the exact opposite. The people who were less sensitive to testosterone were more aggressive, because their body made more of the stuff in an attempt to get the same effect.

Another stress hormone, cortisol, might trigger sudden spontaneous aggression. When researchers triggered the release of corticosterone - the equivalent to human cortisol - in rats, the rats would attack whatever was nearby. When the rats had their adrenal glands removed, but were injected with the hormone, they would again attack, even if there was no threat. Hormones can provide only occasional bursts of aggression - nothing anyone would associate with actual evil as a personality trait.

Brain Injury

This is what Terry Johnson thinks is the thing that would be the most likely to turn someone into an 'evil,' twin, telling io9, "I'd go with brain injury - and a mindbendingly terrible childhood. It would be likeliest to produce evil, though potentially a not very productive evil."

As evidence, at least for the brain injury, he points to a study published by the American Academy of Neurology, which dealt with stroke patients. A full third of the patients found themselves unable to control their anger and aggression in the year following their stroke. The physicians treating them found lesions in the frontal lobe of their brain. This lead to what clinicians termed 'emotional incontinence.' Patients were irritable, angry, depressed, and most of all impulsive. The usual barriers keeping them from following through on their flashes of anger were gone.

Still, it must be said, that even when it came to something physically changing the brain and causing uncontrollable anger, the likelihood of a person developing that kind of response aggression was linked to alcoholism and depression before the injury occurred. And like other physical and emotional problems brought on by strokes, the effects of the lesions could be obliterated as, over time, the patient healed.

So it looks very much like making an 'evil' twin is an extremely difficult thing to do, at least physically. It's undeniable that plenty of twins have different personalities - and some physiology has to be different in order for that to happen. And that people behave in ways that could be termed 'evil' for a lot of different reasons, from personal preference to driving need to uncontrollable impulses. But as with intelligence and ability, how a person is treated is going to be the most likely determinant of what they'll be like. The data agrees, and so does Terry Johnson, who told us that, "Training is almost certainly going to be your best bet."

Sad. But true.

DNA Image: Christoph Bock

Testosterone Image: DEA

Brain Image: everyone's idle

Via CBS, JHU, Psych Central, APA, and Science Blog.