Experiment An experiment is a test of the hypothesis. Experiments are useful in disproving hypotheses. Hypotheses are not proved. This idea will be discussed later. To test the bird predation hypothesis, H.B.D. Kettlewell released moths of each type and then measured the number that were later recaptured. The experiment was performed in a polluted area in Birmingham, England and in a clean area in Dorset. The moths were marked with a dot of paint so that he could identify them after they were released and then recaptured. The bird predation hypothesis (above) predicts that the light form should survive better in the clean area and the dark form should survive better in the polluted area. An estimate of survival can be obtained by using the number of moths recaptured. Obviously, moths that were taken by predators were not recaptured; only survivors were recaptured. Experimental Design Scientists often perform experiments by doing some sort of a manipulation. In the example above, one group of mice was given a hormone and the other group was not. The group of mice that was
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