The Harvard Study of Adult Development, one of the longest-running longitudinal studies in history, plays a significant role in shaping the contemporary understanding of human development and the factors that contribute to a fulfilling life. The study’s findings, which Duhigg discusses in the Afterword of Supercommunicators, provide an important backdrop for exploring the impact of effective communication and social connections in achieving happiness and well-being.

The study began in 1938 as two separate research projects: The Harvard Grant Study and the Glueck Study. The Harvard Grant Study, led by psychiatrist George Vaillant, initially enrolled 268 Harvard sophomores from the classes of 1939-1944, with the aim of identifying the psychosocial predictors of healthy aging. The Glueck Study, led by criminologists Sheldon and Eleanor Glueck, recruited 456 disadvantaged youths from inner-city Boston neighborhoods to study the factors that contribute to delinquency and poor mental health outcomes.

Over time, these two studies were combined and expanded to include the spouses and children of the original participants, creating a multi-generational study that has followed its subjects for over 80 years. The researchers collected data through regular questionnaires, interviews, medical records, and psychological tests, providing a rich and detailed portrait of the participants’ lives.

One of the study’s most significant findings, which Duhigg highlights in Supercommunicators, is the paramount importance of social connections and relationships in determining life outcomes.