Kettlewell field experiments reveal that alternative interpretation of experimental data is important for it helps eliminate historically misleading conclusions that were made by characterizing some popular experiments. Controlled field experiments are difficult to design because, in the case of moths, it was hard to determine the appropriate number of moths to be used for the experiment (Tajchman, 2011). Additionally, it is hard to choose an appropriate environment that would have similar conditions as the natural one. Experimental controls help the researcher identify different characteristics and traits of an organism under investigation. In order for Kettlewell to support his theories, he used the natural selection and adaptive evolution evidences.

If Harrison’s hypothesis had been correct, the rate of mutation would have been 100%. Mathematically, this is proved as follows:

Take ­no denote the number of moths before the experiment and n1 the number of moths that mutated


Following Harrison’s hypothesis, all moth fed with polluted leaves should mutate. This means that no = n1 at the end of the experiment hence;


Harrison may argued out that Fisher’s experiments were wrong and not based on scientific evidence since he (Harrison) had tested the rate of mutation and confirmed it to be 100% and not 0.01% as Fisher had approximated.

Background determined the degree of survival of different types of moths. Moths that camouflage well with the background were likely to survive than those that were highly conspicuous due the background as predators, like birds, could easily spot the moths. Therefore, background is really necessary for natural selection.

Kettlewell and other scientists found out that moths have a superior ability to choose their backgrounds compared to butterflies (Tajchman, 2011). Moths use both olfactory and visual tactics to determine a background that suits them and this made moths like dark backgrounds which apparently were laden with pollution from the industries. Since butterflies did not possess such tactics, they were mostly found in brighter backgrounds were pollution was minimal.

The overall difference in the recapture rates may be as a result of predation from birds. These birds may have preyed upon the moths that were more conspicuous in both the two settings: Birmingham and Dorset, reducing their population significantly hence the likelihood of recapturing twice the marked moths. With the camouflaged moths, it was possible to recapture twice the marked moths since most of them were camouflaged and hence little were preyed upon and therefore their population remained relatively constant.