Empirical Problems Before looking at the empirical problems with evolution, two observations should be noted about the nature of scientific theories and their empirical test. All theories work on paper. Any scientific theory can be described so that it sounds correct, even manifestly correct. The reason why an empirical test is needed is because on paper a theory can make any assumptions it needs to make in order to work. Often, these assumptions turn out to be false when the empirical situation is evaluated.
Negative evidence is more important than positive evidence.
Usually, this is why the theory was formulated in the first place. If many examples of supporting evidence are found, but only a few pieces of negative evidence are found, it might seem that the positive examples outweigh the negative. But empirical evidence does not add up this way. A single piece of strong, negative evidence can destroy a theory. Theories are confirmed not primarily by positive evidence, but by a lack of credible negative evidence.