Abstract: Fundamental to the success of any research project is asking the right question in the first place. In this chapter, Tinbergen's four questions about adaptation, causation, development, and evolution are discussed in the context of the kinds of observations that can be made to answer them. The central point of the chapter (and indeed of the whole book) is that science is about testing hypotheses and hypotheses can be tested just as effectively with observational data as they can with experimental data, with the great advantage that the animals can be studied in their natural environments. The chapter looks at how hypotheses are tested, which may sometimes mean that they are discarded because they do not fit the facts.

Keywords: hypothesis testing, Tinbergen, scientific method, adaptation, causation, development, evolution,