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IB DP Psychology — Biological Approach | SL & HL | Paper 1
🎯 Learning Intentions By the end of this note, you will be able to:
- Define hormones, neurotransmitters, and pheromones using IB-aligned biological terminology.
- Explain how oxytocin influences bonding, trust, and prosocial behaviour in interpersonal relationships.
- Describe the role of testosterone in dominance, aggression, and mate-seeking behaviour.
- Explain how dopamine and serotonin contribute to attraction, romantic love, and relationship maintenance.
- Evaluate research evidence for the role of chemical messengers in relationships using supporting and opposing studies in ACAS format.
- Apply biological concepts to a real-world case study from the biological perspective.
- Discuss the extent to which chemical messengers provide a complete explanation of human interpersonal behaviour.
- Analyse the role of chemical messengers using relevant concept areas: Causality, Bias, Perspective, and Responsibility.
Introduction & Context
Think about the last time you felt an immediate, almost inexplicable sense of warmth toward someone you had just met — or the way a long hug from a close friend seemed to dissolve anxiety almost instantly. These experiences feel deeply personal and emotional, yet beneath them, a complex chemical conversation is taking place inside your body. Your brain and bloodstream are flooded with molecules that shape how you feel about other people, how much you trust them, and how strongly you are drawn to them.
Psychology has long recognised that our relationships are not shaped by conscious choice alone. The biological approach asks us to look beneath the surface of social behaviour and consider the role of chemical messengers — hormones and neurotransmitters — that regulate the emotional and motivational states underlying attraction, attachment, and conflict. Understanding these messengers does not reduce love or friendship to mere chemistry; rather, it reveals one layer of a richly complex picture of why humans relate to one another the way they do.
🔁 Analogy Think of your brain as a city and chemical messengers as the traffic signals and road signs that direct the flow of vehicles. Without these signals, drivers (neurons and organs) would not know when to stop, accelerate, or yield to others. Hormones and neurotransmitters are the city's communication infrastructure — invisible to the naked eye, yet entirely responsible for whether the city runs smoothly or descends into chaos. In the same way, chemical messengers coordinate the invisible infrastructure of your social and emotional life.
Core Concepts
Before we examine individual chemical messengers, it is worth establishing what we mean by the term itself. The body uses two main types of chemical communication: hormones, which travel through the bloodstream and act on distant organs, and neurotransmitters, which transmit signals across synapses between neurons in the brain. Both types of chemical messenger influence mood, motivation, and social behaviour — and both are therefore relevant to understanding interpersonal relationships.
📖 Key Definition — Chemical Messengers Chemical messengers are biological molecules — including hormones and neurotransmitters — that transmit signals within the body to regulate physiological and psychological processes. In the context of interpersonal relationships, they influence emotional states such as trust, attraction, jealousy, and attachment by acting on specific receptors in the brain and body.
With this foundation in place, we can now examine the four most extensively researched chemical messengers in the context of human relationships: oxytocin, testosterone, dopamine, and serotonin. Each plays a distinct but interconnected role, and together they help explain the biological underpinnings of how we form, maintain, and sometimes rupture our connections with others.
Concept A —