What is important of the theory of evolution to modern biology?

All organisms alive today have been, is and will be evolving. Therefore nothing in Biology makes sense except in light of evolution. For example, in medicine, the resistance of bacteria to antibiotics would not make sense except for evolution. If a drug has been killing bacteria so effectively (e.g. penicillin) for decades, why would it start to gradually become less and less effective? The answer lies in the fact that the drug creates an enormous selection pressure in favour of resistance, and this leads to an increase in the proportion of resistant bacteria in each generation. This process is an artificial and miniature version of evolution but it is evolution nonetheless. In nature, the selection pressure is usually much smaller and the process takes much longer (millions of years instead of decades).