Is MAOA gene really unique to people with violent behavior or tendency? There have always been two opinions in the scientific community, one is that there is an inevitable connection, and the other is that there is no inevitable connection. Until 2009, some researchers held a positive view. In 2009, Kevin Beaver of Florida State University found that relatively speaking, boys with MAOA-L gene prefer to join criminal gangs, and the proportion of weapons used in fights is four times higher than that of boys without MAOA-L gene. In his published paper, he declared: "The culture of criminal gangs may be attributed to the' fighter gene'. Boys with this gene may be dangerous. They advocate violence and like to wear weapons. "

Many researchers refuted Beaver's point of view, and the most important evidence was found: a sample survey of whites found that 1/3 of them carried MAOA-L gene, most of them had nothing to do with criminal gangs, and there was no evidence that they were prone to violence. In other words, MAOA-L gene is not a "violent gene", but it is more common in humans. In fact, scientific research has not found a clear pointing relationship between genes and human behavior. Although scientists published the human genome map ten years ago, the relationship between genes and human behavior is still one of the most difficult tasks in biological research. Humans have far fewer genetic genes than originally thought. It is still a very arduous and complicated task to find out how these genes constitute hundreds of millions of different people and how they affect people's behavior.

It is found that there are two types of MAOA genes, one is MAOA-L gene studied by beaver, and the other is MAOA-H gene. Because their activities are different, they have different influences on people. The weak activity of MAOA-L gene will not excite people, but may cause some negative emotions and behaviors, such as sadness, depression, anxiety, attention deficit hyperactivity disorder, anorexia, schizophrenia, nervousness, pathological gambling, smoking and alcoholism. Of course, these negative emotions and behaviors may lead to crime, but they may also lead to self-harm, and these emotions and behaviors are generated under specific circumstances, even people who do not carry MAOA-L gene may produce them. The research shows that MAOA-H gene has little effect on people's mood and behavior, but mainly acts on people's decision-making behavior. For example, MAOA-H gene carriers prefer to take risks, especially investment risks. They prefer to buy stocks rather than insurance.

The study of two types of MAOA genes shows that aggression is not the only association with MAOA, so there is no need to exaggerate the relationship between them. Scientists in Taiwan Province Province of China also found that the highly active MAOA-H gene is related to gout. The pain caused by this disease comes from the excessive uric acid in blood, which has nothing to do with MAOA-H gene, but MAOA-H gene affects the level of dopamine in human body, and dopamine affects the function of kidney to eliminate uric acid, thus producing gout. Other studies have found that women with MAOA-L gene are more likely to suffer from depression during pregnancy, but only if they also carry COMT gene.

It can be seen that MAOA-L gene has only a weak correlation with violence, while MAOA-H gene has no correlation with violence. Therefore, whether it is "fighting gene" or "violent gene", their description of MAOA gene is very one-sided. People's behavior is by no means as simple and clear as the color of their bodies. The rash practice of labeling genes with bad behavior will inevitably mislead the media and the public.