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PY0547_Week 9_Sex Hormones & Aggression

Course Information

  • Course Title: Psychobiology (PYO547)

  • University: Northumbria University, Newcastle

  • Instructor: Dr. Fiona Dodd

  • Week: 9

Overview of Aggression

  • Impacts:

    • Evolutionary function

    • Role of sex hormones (mainly testosterone) and neurotransmitters (serotonin)

    • Implicated brain regions (e.g., pre-frontal cortex)

    • Genetic influences and the nature vs. nurture debate

Definitions of Aggression

  • Aggression Defined:

    • Physical or verbal behavior intended to cause harm, damage, or discomfort.

    • Includes:

      • Physical assault

      • Gossip and ostracization

      • Coercive tactics

Gender Differences in Aggression

  • Both genders exhibit equal levels of verbal aggression.

  • Men display higher levels of physical aggression.

  • Women show more indirect forms of aggression.

  • Reference: Björkqvist K. (2018)

Evolutionary Function of Aggression

  • Fitness:

    • In the animal kingdom, aggression can enhance status and resource acquisition.

    • Aggression increases access to resources and likely enhances reproductive success.

Aggression in Animals

  • Comparison to Humans:

    • Questions regarding whether human aggression parallels animal behavior over mates, territory, and food.

    • Examples: Modern gangs and territory disputes; implications of food shortages.

Biological Factors in Aggression

  • Key Influencers:

    • Hormones (e.g., testosterone, serotonin)

    • Brain regions (e.g., prefrontal cortex)

    • Genetic factors

Hormonal Influences on Aggression

Testosterone Studies in Animals

  • Higher testosterone in monkeys correlates with dominance and aggressive displays (Rose et al., 1971).

  • Castration leads to loss of dominance; testosterone injections can restore it.

  • Hyena Example: Female hyenas dominate males due to size and higher androgen levels (French et al., 2013).

Testosterone and Aggression in Humans

  • Crime rates peak in men aged 18-25.

  • Bidirectional Relationship:

    • Mazur & Booth (1998) notes that increased aggression raises testosterone levels, and vice versa.

  • Presence of women can elevate testosterone in dominant men (van der Meij et al., 2008).

Biological Markers of Masculinity

  • 2D:4D Digit Ratio:

    • Lower ratios in men correlate with prenatal testosterone exposure and suggest aggressive behavior traits.

  • Study by Bailey & Hurd (2005):

    • Found negative correlation between lower 2D:4D ratios and self-reported aggression in males.

    • No correlation found in females for anger or hostility.

Genetic Factors Affecting Aggression

  • “Warrior” Gene:

    • MAO-A enzyme linked to serotonin breakdown influences aggression; its low activity form is associated with higher aggression levels.

  • Study Reference: Capsi et al. (2002)

Brain Regions and Aggression

Role of the Prefrontal Cortex

  • Prefrontal cortex involvement is crucial for impulse control over aggressive thoughts.

  • Damage to this area potentially aggravates aggression due to diminished serotonergic regulation.

Research Studies

  • New et al. (2002): PET studies showed impulsive subjects lacked activation in prefrontal cortex when provided with serotonin boosts, suggesting irreversible damage.

Environmental Influences on Aggression

Nurture vs. Nature Debate

  • Do violent offenders originate from traumatic backgrounds or 'broken homes'?

  • Studies by Raine et al.:

    • Show discrepancies in metabolic activity in violent offenders compared to controls, revealing potential neurological markers.

    • Non-deprived murderers exhibited reduced activity in the prefrontal cortex, suggesting complex influences on aggression behavior should be explored.

Learning Aggression Through Observation

  • Bandura et al. (1961):

    • Children who observed aggression exhibited similar behaviors when interacting with toys, highlighting the role of social learning theory in aggression.

Ethical Considerations

  • Bandura’s Experiments:

    • Although notable for their controlled variables, criticisms include concerns over artificial violence and demand characteristics.

    • Long-term aggression effects remain an understudied area due to immediate measurement post-experiment.

Conclusion: Nature vs. Nurture

  • Aggression may stem from a combination of biological mechanisms (nature) and environmental influences (nurture).

  • Ongoing discussions in the field encourage a dual perspective on aggression's origins.

Assessment and Further Activities

  • Future Workshop: Exam revision session scheduled for December 4th to prepare for the January assessment.