Charles Darwin, not Albert Einstein, is the more appropriate role model for psychologists because he did not begin the Beagle voyage with a favorite idea he wished to prove. Rather, he was open to pursuing any puzzling observation without prejudice. Fortunately, nature furnished the evidence that his intelligence recognized as inconsistent with popular ideology. The rest is history.

I made the few modest discoveries that brought me a small measure of recognition because I adopted Darwin's strategy. I distrusted a priori hypotheses and remained vigilant for observations that were reliable and appeared to be related to a theoretically important issue. When chance presented such observations, I pursued them with the methods available at that time.

This approach generated several discoveries that, I hope, contributed to a deeper understanding of human development. The unexpected observation, in the 1970s, of an increase in attention to faces by infants of seven to nine months old implied an enhancement in working memory due to the maturation of a circuit connecting the temporal and frontal lobes. This discovery, which was later confirmed by others, was satisfying because it explained why seven to nine months is the interval when most infants cry when a stranger approaches them too quickly or their mother leaves them alone for a few minutes in an unfamiliar room. Infants cry because they compare the event with their acquired knowledge and cannot resolve the discrepancy. That comparison requires an improved working memory.

The research on temperament, conducted over the past thirty-five years, has brought more satisfaction, partly because most psychologists regard the discoveries as more significant. Hence, this short essay describes the events that led to the invention of the concepts of high- and low-reactive infants and inhibited and uninhibited children.

These ideas had their origin in the early 1960s, when Howard Moss and I were studying a large group of twenty- to thirty-year-olds on whom extensive observations from infancy to late adolescence were available. A small number of adults whose personality was marked by caution, uncertainty, and a risk-averse posture to challenge typically also had retreated from unfamiliar people or events during their first three years. A second, equally small group showed the contrasting profile of an exuberant approach to, rather than avoidance of, unfamiliar people, objects, or places.