Parents who've been told that one of their children has a behavioural or emotional problem often ask me: "How can it be that my children have turned out so differently, when we treated them all exactly the same?"
Every child is unique - although, surprisingly, one study found that children are likely to be more like their classmates than their siblings. The researchers argued that this is because children try harder to distinguish themselves from their siblings than from their peers, so that their parents will regard them as individuals. Whether or not this is correct, children in the same family often have very different personalities, even when they are twins.
Personality - those characteristics that determine how we think, behave and feel - is a complicated issue. Thankfully, no psychologist still believes personality is entirely inherited or entirely learnt. Everyone now agrees that personality results from an interaction between our experience and our genetic make-up. It's also accepted that no one will behave consistently in all situations. Our environment helped form our personality and it continues to exert an effect by testing the strength of our characteristics. It's also agreed that three environmental factors influence personality development most - the attitudes and rules of the culture we grow up in, the way we're parented, and our birth order position.
There's less agreement when it comes to choosing the most powerful personality traits, the ones most resistant to environmental influences, which can be assumed to have the highest genetic loading. The current view is that there are five: extroversion (outgoing, sociable), neuroticism (prone to negative emotions), agreeableness (trusting, easygoing towards other people), conscientiousness (organised, efficient, disciplined), and openness to experience (curious and unconventional). Even these can change if the environmental pressures on us are powerful - and if we are determined to change.
How can this information help parents puzzled by a "problem child"? Most of all, I hope it gives them hope. Personality theorists have shown us that any characteristic can be modified, although some - conscientiousness or sociability - will be harder to shift than others, such as assertiveness or honesty.