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The Nature of Science Science is a way of gaining knowledge through critical observation and exper- iment. Humans try in many ways to explain their universe, through music, art, literature, religion, philosophy and science, for example. While many of these approaches may provide answers that we seek, only one, science, is based on empirical tests about nature that can be repeated and verified.

All sciences—including physics, chemistry, molecular biology, geology, and biological anthropology—are based on three assumptions. The first assumption is natural causality, which states that all events in nature are due to natural causes. Thus, scientists assume that everything can be explained by natural means, without reference to a supernatural power or force. Scientific explana- tions, then, deal with cause and effect—the idea that one thing is the result of another, as opposed to teleological explanations, which believe that nature has a supernatural design and a purpose. The second assumption is uniformity in space and time, which states that all events occur in the same way wherever or whenever they may happen in the universe. Therefore, natural laws, such as gravity, do not change over time or distance. The third assumption is common perception, which states that all humans perceive events through their senses in the same way, although morals or ethics may vary. For example, all humans can perceive the color red in the same way through their visual system; however,

C h a p t e r 1

The Scientific Method

After completing this chapter you should be able to:

1. determine the difference between science and other ways of knowing;

2. know the assumptions that all sciences are based upon;

3. describe the basic steps of the scientific method;

4. design a simple experiment to test a hypothesis; and

5. describe the design of a typical scientific research article.

O b j e c t i v e s

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2 Chapter 1

Hypothesis

Observation

DATA

Experiment

Hypothesis rejected, supported or refined

in some societies red is the color of good luck or fortune, while in other cultures red may symbolize death.

EXERCISE 1

Some people claim that epileptic seizures are the result of a supernatural

force being directed at a person for punishment of past behavior. Is this a

statement of cause and effect or teleology? Does it violate any of the

assumptions above? If so, which one?

____________________________________________________________________

Others claim that epilepsy is the result of neurons misfiring in the brain of

afflicted individuals. Does this statement represent cause and effect or

teleology? Does it violate any of the assumptions above? If so, which one?

____________________________________________________________________

The Scientific Method The scientific method is a process for empirically testing possible answers to questions about natural phenomena in ways that may be repeated and verified. The questions arise from our observations of the world around us. The answers that result from the testing are added to the body of knowledge we have about the natural universe. Scientific explanations are always subject to updates and modifications based on further testing (see Figure 1-1). The scientific method generally has the following steps (an example is provided for each step):

1. Observation. A researcher may make observations directly from nature with his or her own senses, or from the written words of other investigators who have published scientific articles that are available in university libraries. Either way, the observed phenomenon must be repeatable—something that can be observed more than once.

Figure 1-1 The Scientific Method.

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The Scientific Method 3

• Observation: Historically, a scientist observed that maggots were found associated with spoiled meat.

2. Formulate a research hypothesis. A hypothesis is a proposed explana- tion for the observed phenomena (i.e., a general answer statement to the question). • Hypothesis: The maggots arise through spontaneous generation on

spoiled meat.

3. Experiment. All hypotheses must be testable. The testing, or experi- mental, stage produces more information (data) about the original obser- vation that may or may not support the hypothesis. This stage is often repeated multiple times, by different researchers, who may not have been involved in the original observations. • Experiment: Spoiled meat was placed into two containers, one with no

lid and another with a tightly secured lid. Both containers were left in one room for several days. As the experiment proceeded, flies entered the room and laid eggs on the meat in the opened container. The eggs later hatched into maggots. The meat in the covered container was unaltered.

4. Form a conclusion. This may or may not support the original hypothe- sis. It is based on the data collected and tested in your experiment and has some validity, or support. • Conclusion: The hypothesis was wrong. Maggots do not appear via

spontaneous generation but are the larvae produced by fly eggs.

Sometimes, countless experiments by numerous researchers working in many different countries all support the same conclusion and stand the test of time. In these cases, the validity of the results is not seriously doubted by the sci- entific community, and the conclusion may be considered a scientific theory. All scientific theories have been rigorously and exhaustively tested and are sup- ported by a significant body of data. Often the lay public believes that theories are just hunches or not well-supported claims; however, this is a common mis- conception. Theories continue to be tested and may be modified in the light of new knowledge, especially as we advance technologically. Some examples of modern scientific theories include gravity, the germ theory of disease, heliocen- trism, and evolution.

Experimental Design Experiments test hypotheses. Specifically, they test the relationship between two (or more) variables. Does a change in one variable, cause a change in the other variable(s)? In any test, there are three kinds of variables. The independent variable is the condition or event under study. The dependent variable is the condition or event that may change due to the independent variable. The control variables are all the other conditions and events, which the researcher attempts to keep the same. Control variables are also independent variables, but they are held constant, whereas the independent variable may be altered in the experi- ment. It is not always easy to identify all the variables that may affect an experi- ment. Reading about other people’s work is also important because it helps to familiarize us with what has already been done, helps us define the variables, and helps prevent us from repeating the same mistakes others have made.

■ In the preceding maggot example, the dependent variable is the presence/ absence of maggots; the independent variable that was altered is the open/closed container. The room temperature, humidity, amount of light, and so on are all independent variables that can be controlled in the experiment.

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4 Chapter 1

There are two types of experiments:

1. Controlled experiments. These occur when an investigator designs an experimental situation, usually in a laboratory. The researcher can alter one variable (the independent variable) and see what effect it has on the other variable (dependent variable). In all controlled experiments, one group should remain unchanged and unaltered in any way: the control group or comparison group. This control group is used as a baseline from which to compare the other group(s).

2. Natural experiments. The researcher has little or no control over any of the variables in natural experiments. Such experiments are common in animal behavior studies, where an investigator spends a considerable amount of time in the field observing subjects and taking careful notes of their observations. This type of experiment is common to some branches of the natural and social sciences.

EXERCISE 2

An experiment is done to test the effect of a new experimental drug for high cholesterol. Two hundred volunteers are separated into two groups of 100 each. Both groups are instructed to follow their regular diet and activities. Group 1 is given the experimental drug daily for 90 days, while Group 2 is given a placebo. The individuals in the groups do not know whether they are taking the new drug or the placebo. All participants are tested at the start of the study for their serum cholesterol levels. The average for Group 1 is 310 mg/dl, and the average for Group 2 is 302 mg/dl.

After 90 days, all participants’ serum cholesterol is tested with a blood test. The average serum cholesterol level for Group 1 is 299 mg/dl, and the average for Group 2 is 300 mg/dl.

Using this information answer the following:

a. What is the hypothesis being tested?_________________________________

___________________________________________________________________

b. What is the dependent variable?_____________________________________

___________________________________________________________________

c. What are the independent variables?_________________________________

___________________________________________________________________

d. Which variables are controlled?______________________________________

___________________________________________________________________

e. Which is the control group?__________________________________________

___________________________________________________________________

f. Did the experiment produce data that supports the hypothesis?_________

___________________________________________________________________

EXERCISE 3

An experiment is done to test the effect on mice of a high-fat diet. Fifty weanling mice are separated at random into two groups of 25 each. Group 1 is fed a nor- mal diet with balanced amounts of protein, carbohydrates, vitamin supplements,

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The Scientific Method 5

and fat. Group 2 is fed the same amount of protein, carbohydrates, and vitamin supplements but is given a much higher fat content. The cages are cleaned and mice are given fresh food and water daily.

After six months, all mice are weighed. The average weight in grams for Group 1 is 8.2 g. The average weight for Group 2 is 12.6 g.