BIOL 217 SCIENTIFIC METHOD Page 1 of 2 The hypothetico‐deductive method is the major approach that scientists use to enhance our understanding the natural world. The key feature of the H‐D method is hypothesis testing. For science to advance, three critical elements are needed: observation, hypothesis, and experimentation. Before attempting to explain anything about an ecological phenomenon, we must first observe it. Once we have made an observation or a set of observations, we must recognize that there is a problem to be solved. Alternatively stated, we must ask questions about the observed data. We next consider possible answers to our questions, possible explanations for the observations. Generically speaking, a hypothesis is a tentative, unproven explanation for some observation(s). In science, a hypotheses must be testable. For example, we cannot test the hypothesis that the sky is blue because undetectable genies painted it. A null hypothesis (H0) states that a relationship is not true, that there is no difference between groups. In ecology there are two major stages that require use of null hypotheses. First, we gather descriptive field data that are tested statistically to establish whether or not there are real differences to be explained. If we cannot reject Ho, there is nothing to explain. If Ho is rejected, we next try to develop hypotheses to account for the observed difference. Hypotheses are hunches, which may well be wrong. They must be tested. At the explanatory stage, testing is ideally done experimentally. An experiment is a procedure conducted to test alternative hypotheses. The great advantages of experimentation are that it allows us to disprove hypotheses and to isolate the effects of single factors on the phenomenon being studied. Experiments may be of two general sorts, those classic experiments in which we manipulate some variable to observe an effect, or “pattern analysis”, wherein we look for patterns in the world around us and infer some meaning to them. As an interesting philosophical aside, some argue that the latter is not real science, since nothing was manipulated. Biology yes, but maybe not science. In an experiment we can control the effects of all but one variable. We study the effects of differences in the experimental treatment variable (independent variable) on a second variable (dependent variable), which may or may not be affected by the independent variable. If we can establish that experimental manipulation of the independent variable is associated with differences in the dependent variable, we can than say that the differences in the independent variable cause the differences in the dependent variable. In contrast, nonexperimental correlations between variables observed in the field cannot establish causation. A theory is an explanation of observed patterns based on numerous supported hypotheses. A paradigm is a theory that has become so well supported that is assumed to be true, and as such becomes the foundation for further theoretical development. Evolution by natural selection is a paradigm in biology. EXAMPLE Suppose we have casually observed that a human population sampled in China appears to be shorter, has lower heart attack rates, and consumes less protein per capita than a sample population from Canada. 1) How would we determine whether these apparent differences are real? 2) If the differences cannot be shown to be real, what should be done next? 3) If the differences are real, suppose we simply measure the height and amount of protein in the diets of the several human populations. What are the possible findings for size versus protein consumption? What can be concluded? If size and heart attack rates are correlated, can we conclude that small size confers protection against heart attacks? Is the high potential for heart attacks rather than high protein levels the cause of large size? 4) Suppose that we hypothesize that the mean height differs in the two human populations due to amount of protein in the diet during childhood. What would Ho be? 5) Devise a controlled experiment to determine the effect of dietary protein level on height in the two populations. What are the predictions and possible findings? 6) How might you exclude potential for heart attack as a factor affecting height?