Hormones and genes in aggression

Introduction to Hormones and Genes in Aggression

Welcome! In this chapter, we are looking at the biological reasons why people might behave aggressively. Instead of looking at how someone was raised or what they are thinking, we are looking deep inside the body at our "internal chemistry" (hormones) and our "biological blueprints" (genes).

Biological psychology assumes that our actions are controlled by physical processes. If we can understand the chemicals and DNA that make us up, we can understand why some people might be more prone to aggression than others. Don't worry if the science feels a bit heavy at first—we will break it down step-by-step!

1. The Role of Hormones in Aggression

Hormones are chemical messengers produced by the endocrine system. They travel through the bloodstream to help regulate different body functions. While the central nervous system (CNS) uses fast electrical signals, hormones are usually slower-acting but have long-lasting effects on behavior.

Testosterone: The "Aggression Hormone"

The primary hormone linked to aggression is testosterone. It is an androgen (male sex hormone), though it is present in both males and females. Research suggests that higher levels of testosterone are often associated with higher levels of aggressive behavior.

• The Mechanism: High levels of testosterone can influence the brain's limbic system (the part of the brain that handles emotions) and reduce the activity of the pre-frontal cortex (the part that helps us control our impulses).
• Observation: Males generally have higher levels of testosterone than females and, statistically, show higher levels of physical aggression. This provides a biological correlation between the hormone and the behavior.

Real-World Example: Think of testosterone like a "volume knob" for emotions. If the volume is turned up too high, a small provocation might lead to a loud, aggressive response.

Key Takeaway

Hormones like testosterone are chemical messengers. Higher levels of testosterone are correlated with increased aggression, likely because they affect how the brain processes emotional threats and impulse control.

2. The Role of Genes in Aggression

If hormones are the chemicals currently in our system, genes are the instructions we inherited from our parents. Biological psychologists want to know if some people are "born" more aggressive because of their DNA.

The MAOA Gene (The "Warrior Gene")

The most famous gene linked to aggression is the MAOA gene (Monoamine oxidase A). This gene provides instructions for making an enzyme that breaks down neurotransmitters like serotonin, dopamine, and noradrenaline in the brain.

• MAOA-L (Low Activity Variant): Some people have a version of the gene that produces less of the enzyme. This means neurotransmitters are not broken down efficiently.
• The Result: When these neurotransmitters build up, it can lead to problems with mood regulation and an increased likelihood of aggressive outbursts, especially when the person is provoked.

Did you know? The MAOA gene is often called the "Warrior Gene" because people with the low-activity version have been found to react more aggressively in laboratory experiments when they feel they have been treated unfairly.

Quick Review: How do Genes and Hormones differ?

1. Genes: Inherited instructions (DNA). They are constant from birth.
2. Hormones: Chemical messengers in the blood. Levels can change depending on age, time of day, or stressful events.

3. Key Research into Biological Aggression

To prove these biological theories, psychologists conduct research. In your exam, you may need to refer to these specific studies:

McDermott (2008) – MAOA and Provocation

This study investigated how the MAOA gene interacts with the environment. McDermott found that participants with the low-activity MAOA gene (MAOA-L) were more likely to act aggressively (by forcing a "victim" to eat hot spicy sauce) than those with the high-activity version, but only when they were provoked. This shows that biology (genes) and the environment (provocation) work together.

Brendgen et al. (2005) – Twin Studies

Psychologists use twin studies to see if behavior is genetic. Monozygotic (MZ) twins share \(100\%\) of their DNA, while Dizygotic (DZ) twins share \(50\%\).

• The Findings: Brendgen found a higher correlation for physical aggression in MZ twins compared to DZ twins. This suggests that physical aggression is strongly influenced by genes.
• Social Aggression: Interestingly, social aggression (like spreading rumors) was found to be more influenced by the environment than by genes.

Helpful Hint: If a behavior is purely genetic, MZ twins should behave almost exactly the same (\(r = 1.0\)). If they don't, we know the environment must play a role too!

4. Evaluating the Biological Explanation

When studying Psychology (XPS01), you must be able to evaluate (look at the strengths and weaknesses) of these theories.

Strengths (AO3)

• Objectivity: Measuring testosterone levels through saliva or blood tests, or identifying genes through DNA samples, is highly objective. It doesn't rely on someone's opinion; it relies on hard data.
• Scientific Credibility: This approach uses laboratory experiments and brain scanning (like PET or fMRI scans), which are highly controlled and have high reliability.
• Practical Application: If we know aggression is biological, we might be able to develop medical treatments or interventions to help people manage their behavior.

Weaknesses (AO3)

• Reductionism: Critics argue that focusing only on genes and hormones is "reductionist." It reduces a complex human behavior (aggression) down to simple chemicals, ignoring the person’s upbringing, culture, or social situation.
• Cause and Effect: In hormone studies, it is hard to tell if high testosterone causes aggression, or if being aggressive causes testosterone to rise. This is a problem with validity.
• Generalisability: Much of the early research on hormones and aggression was done on animals. Because human brains are much more complex, we must be careful when generalising those results to humans.

5. Summary Checklist

Before you move on to the next chapter (which covers "Brain Structure and Aggression"), make sure you can answer these questions:

• Can you define what a hormone is and name the one most linked to aggression?
• Do you understand that testosterone is a correlation, not necessarily a direct cause?
• Can you explain how the MAOA gene affects the brain's chemistry?
• Can you explain why twin studies (like Brendgen et al.) are useful for studying genetics?
• Are you aware of the McDermott (2008) study regarding provocation?

Common Mistake to Avoid: Don't say that people with the MAOA-L gene are "born criminals." Biology only gives us a predisposition (a tendency). The environment still plays a huge role in whether that aggression actually happens!