Lecture Notes on Aggression and Human Behavior

Human Aggression: An Updated Perspective

Challenging Previous Assumptions

• Initial statement about human aggression needs revision based on 40 years of subsequent scientific advancements.
• Genetic methods allow for the reconstruction of phylogenies, illustrating relationships between humans and other animals, especially primates.
• These methods help estimate the evolutionary timeline from earlier primate forms.

Evolutionary Roots of Aggression

• Over 100 million years ago, mammals diverged into marsupials and other groups.
• Modern marsupials exhibit lower levels of aggression compared to other mammalian groups.
• Rodents branched off, showing that modern rodents are less violent than non-rodent mammals.
• Primates evolved, with tree shrews displaying less homicidal behavior than other primates.
• Humans have inherited a propensity for homicidal violence, evident in the increasing intensifications seen throughout mammalian evolution.
• Humans are among the more homicidal species, comparable to chimpanzees.

Chimpanzee Violence: A Closer Look

• Chimpanzees, despite perceptions, exhibit significant violence.
• Research from 1999-2009 documented chimpanzee killings between groups.
• Boundary patrols: Chimpanzees actively patrol territories, seeking chimpanzees from other groups.
• Territorial disputes: Chimpanzees engage in opportunistic encounters, sometimes leading to the elimination of rival groups.
• High death rate: Chimpanzee violence results in a high mortality rate (approximately two deaths per year in groups of 40-50).

Evidence from Early Human Skulls

• Analysis of pre-agricultural European skulls reveals significant head trauma (26% of well-preserved skulls).
• Forensic methods applied to 30,000-year-old skulls indicate intentional bashing.
• Skeletal remains found thrown in a lake show trauma from spears, arrows, or blunt force, suggesting violent deaths within a cultural group.
• Some remains indicated the individuals were bound, with at least one being pregnant.

Genes and Aggression

• Rather than single "genes for aggression," genes contribute to brain system development.
• Evolution and selection can lead to aggressive behavior due to the adaptiveness of aggression.
• Animal behavior studies explore the functions of aggression in non-human species.

Functions of Aggression

• Establishing hierarchy: Aggression helps determine an individual's position and access to resources.
• Deterring rivals: Aggression incapacitates or eliminates rivals.
• Defense: Aggression defends against attacks and resource theft.
• Reputation: Humans use aggression to acquire and defend their self-image.
• Aiding kin: Aggression benefits friends, family, and offspring.

Bird Wing Signals

• Birds utilize wing gestures as visual signals during conflicts.
• These gestures can resemble aggressive displays, like "flipping the bird."
• Physical attacks are rare but devastating, so birds use signals to resolve conflicts.

Human Aggression: Retaliation and Honor

• Humans use aggression to respond to provocations like insults, theft, or dishonesty.
• Retaliation serves to defend against ongoing attacks and deter future harm.
• FBI records show that arguments are a frequent precursor to homicides (~25%).
• Trivial incidents can escalate to murder when individuals feel disrespected.
• Revenge is a fundamental human desire.

Laboratory Studies on Aggression

• Provocation in lab settings shows individuals are more likely to aggress against the provoker than a third party.
• Aggression is often responsive to provocation, particularly attempts to diminish self-esteem.

Thomas Hobbes and the Leviathan

• Hobbes argued that a powerful entity (Leviathan) is needed to prevent humans from constant conflict ("war of all against all").
• In a state of nature, defense relies on individual willingness to use force.
• Advertising a willingness to victimize others is vital for self-preservation.
• Hamilton's death exemplifies Hobbesian obsession: seeking higher valuation from others by being ready to damage a perceived offender.

Neural Systems Regulating Aggression

• Humans possess neural systems to regulate aggression.
• All vertebrates have two systems that take in information from the environment to manage aggression.
• A direct motor pathway creates innate, reflex-like aggressive responses utilizing sensory cues.
• Olfactory cues play a role in aggression, specific to each species.