What Is a Hypothesis and How Is It Tested

A hypothesis is a conditional explanation of an observation, or series of observations, that typically proposes a cause for the observations (Fig. 2.3). A hypothesis results from asking the questions:

■ "What caused the observed fact?"

■ "How did the observed fact occur?" and

■ "Why did the event that I observed happen, and not some other phenomenon?"

Important characteristics of a hypothesis are that it must be:

1 testable;

2 falsifiable;

3 based on independently verifiable and observable factual information; and

4 used to make predictions.

In paleontology, the last of these qualities is about predicting future discoveries rather than future experiments, because all fossils and sediments that covered them occurred in the past. Paleontologists, therefore, make retrodictions, not predictions.

Testing a scientific hypothesis means that another observer can make more observations repeatedly with regard to the hypothesis. An idea that does not have

FIGURE 2.3 Example of the difference between fact and hypothesis, as well as description and interpretation. Facts: Two features occur on the surface of a rock in Big Bend National Park in western Texas, USA. Both features show semi-circular and crescentic lines emanating and expanding from a point, but one feature is larger than the other and the larger one is also concave, whereas the smaller one is convex. Hypotheses to explain the features:

1 They are completely unrelated forms of unknown origin;

2 They are odd patterns made in the rock when it fractured on this surface and their similarity in form is a result of the uniformity of the rock, which controlled the fracturing;

3 They are plant leaves that were bent upward and downward in the sediment soon after they were buried in the sediment that later formed the rock;

4 They are trace fossils made by animals that lived long ago in the sediment, where the animals were progressively feeding out from a central point but one went up and the other went down;

5 They are the outside and inside imprint of animal bodies, where the animals were similar but just had different sizes at the time they were buried;

6 They are carvings made in the rock by Native Americans, before Europeans settled in the area, that symbolize the light coming from the sun (the larger one, because it gives more light) and the moon (the smaller one because it gives less light, and also carved in opposite relief to the "sun" to symbolize the opposites of night and day).

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