More than half a century ago, Phil A. Silva conceived a study that changed our understanding of human development. In 1972, in the southern New Zealand city of Dunedin, he began an ambitious research project that included every child born in the city over the course of a single year. He probably did not imagine at the time that he was laying the foundations for one of the most influential, thorough, and long-lasting studies ever conducted on a large group of people.

The Dunedin Longitudinal Study soon proved to be a real treasure trove of knowledge. The original plan to follow the children until the age of three was expanded. Researchers began inviting participants back for detailed examinations every few years. Over time, the laboratories accumulated an enormous amount of data, covering everything from mental and physical health to personality traits, social relationships, financial circumstances, and even genetic predispositions.

Over time, the researchers began to discern complex patterns and connections within this vast body of information, revealing links that no one had ever noticed before. More than 1,400 scientific papers have been published so far, many of which have become key references in psychology, medicine, sociology, criminology, genetics, and public health.

The first findings already pointed to an unexpectedly large proportion of three-year-olds with developmental and behavioral difficulties. It also became clear that mental health problems often begin in childhood. Another surprising discovery was that a large share of people experience at least one period of mental distress by the time they reach middle age.

The study also greatly strengthened our understanding of the close connection between mental and physical health. Long-term data showed that poor mental health affects more than just one’s current well-being; it can also lead to poorer physical health and even accelerated biological aging. People with long-standing mental health problems were often in worse physical condition by middle age and showed signs of faster wear and tear of bodily systems. The reverse is also true: chronic physical illnesses or inflammatory processes can negatively affect mental well-being.

These findings highlight the importance of integrating mental health care into general health systems for the entire population, since temporary episodes of psychological distress are more the rule than the exception. The researchers also discovered that people age at remarkably different rates — differences in biological age among individuals born in the same year can be surprisingly large, revealing the influence of lifestyle, environment, and genetic factors on the aging process.

One of the most striking and widely discussed findings of the Dunedin Study concerns the influence of personality traits, especially self-control, on the course of a person’s life. The researchers found that individuals who, already as children, had difficulty regulating their impulses, persisting with tasks, and thinking prudently tended to face far greater difficulties as adults. Children with lower levels of self-control were later in life more likely to experience poorer physical health (such as obesity, high blood pressure, or frequent infections), various forms of addiction (including smoking, alcohol, or drug use), financial problems (debt, lack of savings), and criminal behavior. Even when intelligence and social background were taken into account, self-control remained an exceptionally strong predictor of life success.

A groundbreaking study published by Terrie Moffitt and Avshalom Caspi, who joined the research team in the 1990s, provided evidence that self-control can be strengthened. Children who improved their ability to regulate themselves as they grew up achieved better outcomes than their initial assessments would have predicted. This carries an important message: investing in the development of self-control skills during childhood can be highly beneficial, both for individuals and for society as a whole.

In the 1990s, the research team also began exploring genetics. They discovered that certain genetic variants, such as those in the MAO-A gene, can increase the risk of violent behavior, but only among individuals who experienced severe abuse or maltreatment in childhood. These findings highlighted the importance of the interaction between genes and environment and encouraged discussions on preventive measures to protect children from traumatic experiences.

One of the greatest strengths and defining features of the Dunedin Study is its exceptionally high level of participant engagement. Even after fifty years, nearly 94 percent of the original members remain active in the research, which is remarkable compared to other long-term studies that typically struggle with high dropout rates. The key to this extraordinary commitment lies in the trust and strong bond that has developed between participants and researchers. The team consistently emphasizes that the participants are the true heroes of the study, as they continue to respond to invitations for extensive and sometimes exhausting assessments, believing that their involvement contributes to knowledge that will benefit future generations. Researchers even visit them while they are serving prison sentences, and some participants see their continued involvement in the study as their main contribution to society.

The team is now preparing for a new round of assessments at the age of 52. They plan to use the latest tools, including whole-genome sequencing and gut microbiome analysis. The careful, decades-long tracking of an entire generation of Dunedin residents provides an invaluable source of data for science and a solid foundation for designing compassionate and equitable health and social policies around the world.

Translated from the Slovene original, available here: Življenja pod drobnogledom znanosti.

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THE ANATOMY OF KNOWLEDGE

What a Thousand Lives Reveal