Biochemical battle in the brain determines your temper

In an unborn baby’s brain, four biochemicals – dopamine, serotonin, testosterone and oestrogen – compete to influence how nerve paths are laid out between the different centres of the brain, and so how the baby’s basic personality is formed. Dopamine and serotonin contribute to determining the paths of nerve signals through the brain, and depending on which gets the dominant role, the person may become broadly curious and energetic, or cautious and responsible. The two sex hormones influence the sizes of different brain centres. Where testosterone is dominant, it seems to contribute to an analytical and straightforward temperament, whereas if oestrogen has the upper hand you may become more helpful and compassionate.

At the age of two, children start to develop self-consciousness and social skills, feeling pride, embarrassment and shame, and becoming aware of their own needs. In the beginning, the innate temperament is crucial in determining what a child is willing to do to satisfy various needs, but this changes at the age of 6-9, when the adrenal glands begin to produce rising quantities of the hormone DHEA, which stimulates the growth of brain neurons and so the brain’s continued development.

The hormones further influence the personality, so children this age may develop lower self-esteem or become more aggressive. The quantity of hormones and the neurotransmitters serotonin and dopamine rises and falls abruptly in the teen years, considerably changing the chemistry of the body and the brain. These variations can lead to mood swings and reduced impulse control, which is why young people can act spontaneously with fewer fears about consequences. This can be compounded by a need to follow the example of others to secure position in the social pecking order, which can make teenagers experiment with personalities that may have little influence on their later life.

The biggest and most permanent personality changes happen in the early years of adulthood, when radical changes in life require responsibility for education, work, a home, and a family. Many people experience increased emotional stability and become calmer during this period.

Although menopause and midlife crises later in life can briefly influence the personality, long-term changes in middle-aged people primarily involve them becoming more trusting and cooperative, or opening up to new interests such as art and culture.