The consistent pattern of men committing mass violence is rooted in biological evolution. Men are wired for aggression and physical confrontation, a trait historically selected for by women seeking protectors. This is a biological reality, not a surprising social anomaly.

Neurons for fear and offensive aggression are located closely together in the hypothalamus. Activating these fear neurons can immediately stop a fight, causing the animals to freeze. This reveals a functional hierarchy where the fear state is dominant and can override aggressive impulses.

Aggression is not a switch that flips but a sequence of neural circuit activations with a beginning, middle, and end. Understanding it as a verb or a process allows for intervention at various stages—preventing its initiation, halting it mid-course, or even prolonging it if adaptively necessary.

High levels of the stress hormone cortisol, combined with low levels of serotonin, increase the "hydraulic pressure" for aggression. This state primes the sympathetic nervous system for reactivity. Managing cortisol through tools like sunlight exposure, sauna, or ashwagandha can directly reduce the biological tendency toward aggression.

The common belief that testosterone causes aggression is incorrect. Testosterone is converted into estrogen in the brain via an enzyme called aromatase. It is this brain-derived estrogen binding to specific receptors that directly activates the neural circuits for aggression in both males and females.

Proactive aggression can stem from a neurological difference where the brain doesn't learn from mistakes through fear. The negative consequences that deter most people don't register. Instead, the harmful behavior might produce a reward signal, motivating the individual to continue rather than stop.

The brain's deliberative "Pause & Piece Together" system is suppressed by stress, which boosts the impulsive "Pursue" (reward) and "Protect" (threat) systems. This neurological process explains why we make rash choices when tired or under pressure.

Distinct neuron populations control mating and aggression. Activating mating neurons in a male mouse's medial preoptic area during a fight causes it to immediately stop attacking and instead attempt to mate with the other male, demonstrating a clear neural override mechanism between competing social behaviors.

In mice, prolonged social isolation causes a dramatic increase in the neuropeptide tachykinin. This neurochemical surge is directly responsible for increased aggression, fear, and anxiety. A drug that blocks the tachykinin receptor can completely reverse these isolation-induced effects.