Under this scientific method, biologists formulate hypotheses, or predictions, from an existing body of knowledge and then test their hypotheses through experiments. Experiments range from simple to complex, and can be performed on a computer, in a laboratory setting, or outdoors. Technological developments during the twentieth century—including high-speed computing, DNA sequencing, and a wide array of visualization techniques— have opened the door to many exciting lines of biological investigation. Biologists are constantly developing new techniques to test increasingly complex questions, and have even designed experiments to re-create natural events such as hurricanes, forest fires, and floods.

The scientific method can be applied to many, but not all, types of scientific inquiry. Experimental methods cannot directly test hypotheses concerning the processes of evolution because these events took place over the course of millions of years, under environmental conditions that are as difficult to define as they...