What is it that determines personality? Our future health, wealth, and happiness? Why do some people endure such hardships physically, emotionally, and economically, while others lead a relatively well-adjusted, healthy, and happy existence?
These are questions which fascinate Clinical Psychologist Professor Richie Poulton. Poulton spent decades observing people everywhere from kindergartens to maximum security prisons. To answer these questions, you must take a large group of people, and measure their life experiences in a great deal of detail, so that you get a comprehensive picture of the range of human experience, to better understand what makes us who we are.
In 1972, a medical school from a small city in New Zealand embarked on the ultimate nature/nature test. They decided to take every child born in the city that year and follow them for life. For 40 years scientists probed every aspect of their existence - their medical history, job history, habits, personality, genes, sexual activities, criminal offences, relationships, successes, failures... everything. Nothing was off limits. All information was guaranteed to be held entirely confidential, and is one of the reasons for the study's success. Decades later, over 96% of the participants still continue to take part; a remarkable rate, when with most studies there is less than a 50% take-up rate. (One of the secrets of the success of the study, is that participants are flown back, if necessary, for further testing, and for those who are unable to travel or are institutionalized in prison, the study experts come to them.)
The experiment is called The Dunedin Longitudinal Study, and its subjects are now the 1037 most studied people in the world, and the richest source of information on what really makes us who we are. It is highly-lauded and internationally recognized. There is no other significant study in the world which has accumulated the same level of data, including even undesirable behaviours, the way that the Dunedin has.
Results from this study can predict how children are going to turn out as adults. Typical longitudinal studies measure just a couple of metrics. What's special about the Dunedin Longitudinal is that it measured almost every aspect of human behaviour and development, resulting in a complete picture of a human life. From the study of these 1037 people came an avalanche of findings. 1500 papers, over 40 years, have been published in many scientific journals around the world.
Early criticisms to the study centred around the idea that conclusions made about one town in New Zealand couldn't possibly apply to the rest of the world. This often also included a stereotype of New Zealanders. To check and account for this, aspects of the study were then repeated in the suburbs of inner city Pittsburgh... with similar results. The findings demonstrated that there are fundamental truths driving behaviour, regardless of nationality, economic, or ethnic background.
* Cesarean births and left-handedness have no lasting effects.
* Thumb-sucking and bed-wetting are passing phases with no psychological significance.
* Children who slept the least during their early years become the most overweight adults. They also have poorer cognitive function during adolescence, and anxiety problems in their 20s.
* The more TV people watched as children, the more likely they were as adults to have unhealthy cholesterol levels and be cigarette smokers. The amount of TV watching also predicted how they would later do in university and whether they would end up getting a degree. Children who watched the most TV were 3X more likely to leave school without any qualifications. Those who watched the least were 4X more likely to graduate with a university degree, irrespective of IQ or family income.
The Dunedin study found that children can be classified into 1 of 5 basic personality types, and these early character types persist into adult life. It identified these traits in preschooler children, showing that our temperament at 3 is our temperament at 23.
Well-Adjusted: Active; organized; reasonably adaptable; quite social; flexible; resourceful; fit in well socially; make up ~ 40% of the population.
Confident: Go-getters; entrepreneurs; not afraid to take on challenges; a love of thrill-seeking; not necessarily the life of the party but are people with a presence; ~ 28% of the population.
Reserved: Somewhat timid, but not to the point of being paralyzed by it; quiet; a natural tendency to set back, watch, and observe; ~ 15% of the population.
Inhibited: An adult whose shyness tends to interfere with their ability to do very simple things; they have a hard time leaving home and establishing a life for themselves; fearful, anxious, neurotic; closed to experiences; high-strung; don't like novelty; prone to develop depression; Ex: Japan's Hikikomori; ~7% of the population.
Undercontrolled: Grow up to be high-strung, irritable, easily fly off the handle; closed to new experiences; do not like novelty; do not like change in their environment; involved in antisocial activities; have a much harder time adjusting to work lives and prone to long bouts of unemployment; impulsive, prone to hostility, rage, uncontrolled anger, and losing composure; more likely to develop heart diseases, diabetes, lung problems, STDs; ~10% of the population.
The Confident, Reserved, and Well-Adjusted personality types are generally productive members of society. Their mix of mostly positive traits means they tend to do well in life. They're more likely to be happily married, have friends, successful careers, and enjoy better health.
The Inhibited and Undercontrolled personality types tend to create a great deal of trouble and angst, both for themselves, and for the rest of the community. Lifelong negative outcomes are predicted.
Is There a Single Biggest Predictor of a Person's Success?
Is there anything in childhood that predicts who will be successful and who won't?
Yes, there is one trait, in particular, that can be measured in 4 yr olds that forecasts one's later economic, job, status, health, and relationship success. Answer: Self-control.
In almost every measure of success, self-control made a huge difference. High self-control children, as early as age 3-5, became adults who owned their own homes, were business entrepreneurs, had solid jobs, started saving for retirement, and were considered good money managers by their friends who knew them well. Whereas children exhibiting poor self-control became adults who had issues with debt, had their possessions repossessed, bankruptcy problems, and tended to be known as poor money managers by their friends. But the problems are not just financial. Low self-control also produces a range of health problems from obesity, heart disease, high blood pressure and cholesterol, and STDs. They are also more likely to be addicted to tobacco, alcohol, and drugs. Low self-control has high costs.
Are you in command of yourself, or is yourself in command of you? Some people think that they did not choose to explode, "it just happened", while others may feel the same irritation or anger, yet can down-regulate and control it.
One of the best-known demonstrations of self-control is the Marshmallow Test of Stanford University, first conducted in the 1960s. 4 yr olds were placed in a room with a marshmallow, and given a simple choice. Eat the marshmallow now, or hold back for 15 min and receive two. It is a simple but illuminating test of constraining one's impulses.
What promotes self-control?
Warm, balanced, sensitive and responsive parenting beginning in infancy; being firm and consistent in discipline; having peers who have self-regulating behaviour who enforce norms of social behaviour which exhibit control and regulation.
The Good News
The good news is that self-control is not fixed. With dedication, it can be improved. It is a lot harder to change the person than to change what the person does. But by trying to alter behaviour, you can change how the world responds to that person. It doesn't mean it changes the person's personality, but it does change the punishment-reward system the person experiences with certain behaviours.
The Dunedin study found there is something we can teach any child, any person, no matter what their personality type, self-control that can increase their future health, wealth, and happiness. All people benefit from better self-control skills; even those with average control can have an improved life from improving their regulation. These traits are not set in stone. However it also proved that many adult problems begin much earlier in life than previously imagined. The early years are seminal in all sorts of ways, and early intervention is the best predictor of altering one's path for good, but it is never too late to make changes to one's behaviour and improve the chance of happiness and success.
Transposed from the documentary 'Predict My Future: The Science of Us' (2016)