Richard et al. (2014) meta-analyzed data from 14 separate studies and found that Blacks had higher levels of free floating testosterone in their blood than Whites suggesting that testosterone levels may predispose Blacks towards higher rates of crime.
Compounding this, a high percentage of Blacks have dysfunctional versions of the MAOA androgen receptor gene which is a key part of the mechanism by which testosterone has its effects throughout the body and brain.
MAOA’s job is to break down crucial neurotransmitters which can build up in the brain and cause a loss of impulse control and an increase in violence and rage.
The MAOA gene can come in the form of 2, 3, 3.5, 4, or 5 allele. A 3-repeat allele is considered dysfunctional and is what is referred to as the “warrior gene”. A 2-repeat (2R) allele is considered very dysfunctional.
The 2-repeat allele does not produce a protein needed to break down old serotonin. It is strongly correlated to criminality and doubles the rate of violence of the 3R without needing an environmental interaction mechanism. People with a 2-repeat allele MAOA gene have a permanent chemical imbalance in their brain making the person more likely to be agitated, aggressive, and impulsive.
Only 0.00067% of Asians and .5% of Whites have the MAOA 2-repeat allele version, compared to 4.7% of Blacks.
That means Blacks are 9.4x more likely to have the very dysfunctional version of the MAOA gene than Whites. Considering that Blacks are 10x more likely to commit extreme violence and anti-social behavior than Whites, this is very significant.
Exploring the association between the 2-repeat allele of the MAOA gene promoter polymorphism and psychopathic personality traits, arrests, incarceration, and lifetime antisocial behavior
A line of research has revealed that a polymorphism in the promoter region of the MAOA gene is related to antisocial phenotypes. Most of these studies examine the effects of low MAOA activity alleles (2-repeat and 3-repeat alleles) against the effects of high MAOA activity alleles (3.5-repeat, 4-repeat, and sometimes 5-repeat alleles), with research indicating that the low MAOA activity alleles confer an increased risk to antisocial phenotypes. The current study examined whether the 2-repeat allele, which has been shown to be functionally different from the 3-repeat allele, was associated with a range of antisocial phenotypes in a sample of males drawn from the National Longitudinal Study of Adolescent Health. Analyses revealed that African-American males who carried the 2-repeat allele were, in comparison with other African-American male genotypes, significantly more likely to be arrested and incarcerated. Additional analyses revealed that African-American male carriers of the 2-repeat allele scored significantly higher on an antisocial phenotype index and on measures assessing involvement in violent behaviors over the life course. There was not any association between the 2-repeat allele and a continuously measured psychopathic personality traits scale. The effects of the 2-repeat allele could not be examined in Caucasian males because only 0.1% carried it.
Blacks are also more likely to have versions of dopamine genes like ANKK1 and DAT1 that have been linked to antisocial behavior.
A 2012 study using the Add Health data found that the 2-repeat version of the MAOA gene is significantly associated with antisocial behavior and the likelihood of criminality in Black males.