It is because they have a lesser developed prefrontal cortex of the brain compared to other races. This causes them to be more impulsive and spontaneous(and loud, rude, rowdy, annoying as Hell, etc...), in other words they have a harder time controlling themselves and their impulses than non-Blacks do. Besides that they tend to have larger levels of testosterone and other hormones, an overall higher sex drive. This all proves to be a dangerous combination!   FYI this is the function of the prefrontal cortex of the human brain:     This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior. The basic activity of this brain region is considered to be orchestration of thoughts and actions in accordance with internal goals.