Biological Psychology: Darwin’s Theory of Evolution and the MAOA gene

Evolutionary Psychology

• Human brain circuitry was naturally selected to solve adaptive problems like tracking animals, evading predators, acquiring calories, finding mates, and forming social bonds.
• Evolutionary past sheds light on why contemporary humans behave the way we do.

Apes vs Humans

• Similarities: communication, group work, walk upright, use tools, aggressive behaviors.
• Differences: teeth, anatomy, brain size, language, opposable thumbs.

Darwin's Theory of Evolution by Natural Selection

• Genetic Variation: Naturally occurs in a population due to new alleles formed by mutations.
• Selection Pressure: A change in environmental conditions creates a selection pressure, favoring organisms with beneficial alleles.
• Survival and Reproduction: Organisms with favorable alleles survive, reproduce, and pass on desired characteristics.
• Phenotypes Eliminated: Loss of unfavorable phenotypes reduces the gene pool.
• Evolution: The process by which inherited characteristics in living organisms change over generations.
• Survival of the Fittest: Organisms with favorable characteristics adapted to their environment survive and reproduce.
• Natural Selection: Favorable genes are inherited, while genes that do not aid survival are not.
• Genetic Variation: Differences between the genes of organisms in a species.
• Genetic Mutation: A change in DNA sequences alters gene coding and protein function.
• Allele: A different form of the same gene produced during genetic mutations.
• Selection Pressure or Adaptive Problems: Environmental and social factors which determine which characteristics are favourable.
• Aggression: A range of behaviours that can result in both physical and psychological harm to yourself, others, or objects in the environment.
• Sexual Selection: Success of reproduction rather than survival.
• Symbol of genetic fitness.

Aggression: Survival and Reproductive Benefits

• Guarding a partner/mate retention strategies.
• Guarding offspring.

Warrior Gene (MAOA)

• Mono Amine Oxidase A (MAOA) is a gene that codes for the MAO-A protein, carried on the X chromosome.
• Women can carry 0, 1, or 2 copies (XX), while men can carry 1 or 0 copies (XY).
• MAO-A protein normally breaks down excess neurotransmitters like serotonin and dopamine.
• Mutation in MAOA gene causes enzyme malfunction, resulting in continued/sustained synaptic neurotransmission manifesting as aggressive human behavior.
• The 2R allele is the form of the MAOA gene that correlates with more severe violent impulses.
• Too low MAOA-L allele results in a lack of breakdown of neurotransmitters increasing synaptic neurotransmission and resulting in aggressive behaviours.
• Too high MAOA-H allele results in continual breakdown of neurotransmitters decreasing synaptic neurotransmission and resulting in anxiety disorders.

Supporting Evidence for Evolution and Aggression

• Thornhill & Palmer (2000) hypothesize humans have evolved adaptations to rape to obtain otherwise inaccessible partners.
• Chester et al. (2015) found that low-functioning MAOA-L genotype (‘warrior gene’) was linked to greater aggression.
• Mertins et al. (2011) indicated that a high-functioning MAOA-H genotype was associated with greater prosocial behavior, while the MAOA-L allele is associated with antisocial behavior.

Refuting Evidence Against Evolution and Aggression

• Henian et al (2013) refutes the idea of low MAOA-L genotype is linked to aggression instead proposes that low MAOA-L is linked to human happiness in females, no such difference in men explaining gender differences in aggression.
• Freud, Lorenz (1966) suggests that violence exists within everyone due to a basic instinct to dominate.
• Bandura (1966) Social Learning Theory: Aggressive behavior may be observed in the environment and imitated from same-sex role models.