Hormones: What is Testosterone? (SL IB Psychology)

What is a hormone?

• A hormone is a chemical that is secreted by the endocrine glands into the blood stream which then distributes it around the body
• Hormones act slowly (unlike neurotransmitters which are fast) and may take years to fully have an effect e.g. puberty occurs over several years
• The major gland which regulates hormones is the pituitary gland, located at the base of the hypothalamus
• Hormones will have different effects on the body and on behaviour, depending on the nature of the hormone itself e.g. cortisol regulates the stress response; melatonin regulates the sleep-wake cycle

What is testosterone?

• Testosterone is the key male sex hormone that regulates fertility, muscle mass, fat distribution and red blood cell production
• Testosterone levels rise during puberty when males begin to show secondary sexual characteristics e.g. bodily hair, deepening of the voice
• Females produce testosterone but in much smaller volumes than males
• Testosterone has been linked to behaviours such as aggression and competitiveness 
• Some research shows that males in prison for violent offences have higher levels of testosterone than male prisoners convicted of non-violent crimes

Which studies investigate the effect of testosterone on behaviour?

• Zak et al. (2009) – a lab experiment to investigate whether testosterone makes people less generous and less prosocial towards strangers 
• Armstrong et al. (2022) – increased testosterone levels may lead to impulsive and violent criminal behaviour

The study by Zak et al. (2009) can be found in Two Key Studies of Hormones on this site: just navigate the Hormones & Pheromones topic to find it.