Killer instinct (human behaviour)

Killer instinct is a euphemism for ruthlessness. The killer instinct is the ability within a person to take the life of another human being without the psychological inhibition normally associated with taking life. Psychologists generally accept approximately 2% of individuals have a killer instinct, or formally psychopathy; other analysts question whether it can be taught (for example, through military training and/or after societal breakdown). Some argue that while the mechanical action of killing can be taught, the actual instinct to do so remains inborn or can only be brought out through severe abuse.

Often present in fighting, wars and confrontation, it is generally accepted that some humans possess an ability to kill another human in order to achieve a goal. Examples include soldiers, fighters such as boxers, and mixed martial artists, who often display a form of this when trying to finish off an opponent, whereas it is argued that the main goal is to master self-defense in fighting arts. In Mixed martial arts, however, it is not the end goal to kill the opponent, so it is therefore not able to be included. Soldiers commonly report that in combat, it is simplistic to determine which of their comrades "genuinely wish to kill" and which "are merely serving their time." Posture, walking behavior, attitudes towards the battle can be seen on both an preconscious and fully conscious level, with natural killers in a fire team actively seeking out opportunities to end the life of enemy combatants, while careerists seek out safe and/or supportive roles.