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Scientific methods combine observation, experimentation, and logic

Textbooks often describe “the scientific method,” as if there were a single, simple flow chart that all scientists follow. This is an oversimplification. Although flow charts such as the one shown in Figure 1.12 incorporate much of what scientists do, you should not conclude that scientists necessarily progress through the steps of the process in one prescribed, linear order.

Figure 1.12 Scientific Methodology The process of observation, speculation, hypothesis, prediction, and experimentation is a cornerstone of modern science, although scientists may initiate their research at several different points. Answers gleaned through experimentation lead to new questions, more hypotheses, further experiments, and expanding knowledge.

Animation 1.1 Using Scientific Methodology

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Observations lead to questions. To answer those questions, scientists make additional observations, formulate possible answers, and do experiments to test those possibilities. This investigative approach traditionally has five steps: (1) making observations; (2) asking questions; (3) forming hypotheses, which are tentative answers to the questions; (4) making predictions based on the hypotheses; and (5) testing the predictions by making additional observations or conducting experiments.

After posing a question, a scientist often uses inductive logic to propose a tentative answer. Inductive logic involves taking observations or facts and formulating a new proposition that is compatible with those observations or facts. Such a tentative proposition is a hypothesis (plural hypotheses). For example, in the opener to this chapter, you learned that Rachael Bay observed corals growing in pools that reached temperatures known to kill corals. She formulated two hypotheses:

The populations of corals in the warm pools have evolved genetic differences that enable them to survive heat stress (adaptations), or
Individual corals have the ability to adjust physiologically to different thermal conditions (acclimation).

Rachael and her colleagues conducted experiments and made observations to test these hypotheses. How do scientists design experiments to test hypotheses?

The next step in the scientific method is to apply a different form of logic—deductive logic—that starts with a statement believed to be true (the hypothesis) and then goes on to predict what facts would also have to be true to be compatible with that statement. Rachael’s team tested their hypotheses by measuring how corals from the warm and cool pools responded to laboratory experiments that simulated the heat-stress conditions that occurred sometimes in the warm pools. They predicted that the cool-pool corals would bleach at higher rates under the experimental conditions than the warm-pool corals would. That experiment revealed differences between the two populations, but did not reveal whether the differences were a result of long-term evolutionary changes in the populations (adaptations) or short-term acclimation of individuals to their current environments. The researchers therefore looked for genetic differences in the corals living in the warm and cool pools (adaptations). They also looked for differences in gene expression patterns when the corals were transplanted to different environments (acclimation). Did the two populations have fundamental genetic differences, or did the environments they lived in stimulate different patterns of gene expression and therefore physiological acclimation?