Before presenting this punctuated equilibrium theory or PET about knowledge growth and social change, I want to give proper due to all the individuals who have helped me on this intellectual voyage. One of the mantras of contemporary life focuses on the complexity of the world, especially social change processes. My own mantra of an adaptive solution consists of forming diverse (skills, languages, networks, and access to resources— heterogeneous social capital) research teams at each distinctive analytical level. This book and its insights rest on the foundation of multiple diverse teams. Beyond the many interdisciplinary research teams in which I participated, I also want to thank individuals, friends, colleagues, and students who opened doors for me to learn about other countries from particular vantage points and provided special skill sets that I was lacking. Nor should I forget the many funding agencies that were extremely generous to my teammates and myself over the course of my career. Finally, I conclude with a special thanks to my evolving family tree that has sustained me over these past six decades.

This journey began in January 1959 when I was a first- year graduate student at Columbia University. At the time, no courses were offered on the topic of social change. Indeed, as Wilbert Moore (1963) noted in his book, Social Change, the topic had been neglected. I decided at that time to dedicate my professional life to the problem of developing a new theory of social change. But how to do this? I appreciated that the subject matter was too varied for me to comprehend immediately and that I would need to chunk topics into disparate issues and levels of analysis and explore them one at a time. This was at odds with the dominant thinking of the 1960s and remains so even now; the differences between the micro and macro levels are still usually brushed aside. In contrast, I felt that each of these analytical levels had a distinctive reality that could not be reduced to one or the other, despite all the arguments popular at the time (and today) that involve either psychological reductionism/ methodological individualism or describe sweeping tides of macro forces that carry everyone along (i.e., a rising tide lifts all boats).