Tinbergen is famous for emphasizing behavioral fieldwork and experimentation under natural circumstances, for founding the field of ethology, for getting a Nobel Prize, and for mentoring Richard Dawkins. He is known for dividing behavior studies into physiology, development, natural selection, and evolutionary history. In the decades since Tinbergen was active, some of the best research in animal behavior fuses Tinbergen's questions, connecting genes to behavioral phenotypes, for example. Behavior is the most synthetic of the life sciences, because observing the actions of an organism can tell us what all those physical and physiological traits are for. Insights from behavior tell us how traits in one individual impact those in another in ways that challenge our definition of an organism. Behavioral conflict and cooperation among animals has led to theory that explains within-organism conflict and cooperation and human malfunctions of many kinds. Darwin certainly began the evolutionary study of behavior, but Tinbergen brought it forward to the heart of biology. The challenge for the future is to apply concepts from animal behavior across biology with tools that would have amazed Tinbergen.