Three formative experiences in my life primed me for what I like to think is my most important scientific contribution: bringing genetics into the mainstream of psychology. First, when I was in fourth grade in an elementary Catholic school in Chicago, I was suspended from school because of a book I innocently brought to class for a show-and-tell assignment. The book was about Darwin's voyage on the Beagle; at that time, evolution was not mentioned in Catholic schools because it was considered to be a mortal sin to believe in evolution. To my mind, evolution seemed an idea that was beautiful and obviously true. The religious opposition, coupled with my stubbornness, planted a genetics seed in my mind.

Second, when I was a philosophy major at DePaul University in Chicago, I kept trying to think of testable hypotheses to solve disputes in philosophy, until I realized that if you can come up with a testable hypothesis, it's no longer philosophy – it's psychology. This realization made me switch my major to psychology, and it primed me to stay close to data. (My most overused phrase is “it's empirical.”)

The third experience occurred when I went to graduate school in psychology at the University of Texas at Austin in 1970, which, unknown to me when I accepted their offer, had the only graduate program in behavioral genetics in the world. I was completely bowled over by a required course in behavioral genetics about early animal and human studies that suggested substantial genetic influence on many aspects of psychology. Genetics had not been mentioned in my other classes until then, and I was excited to get a first glimpse of the potential impact of this new way of thinking about psychology and society.

As I learned more about psychology, I saw that genetics was generally ignored or even abhorred. The environment was thought to be completely responsible for individual differences in psychological traits – for example, why some children are shy, why some find it difficult to read, and why some are autistic. During the past few decades, my research, and the research of others in the small field of behavioral genetics, has shown that genetics can no longer be ignored.