Protein, the building blocks of proteins are amino acids, different sequences and combinations of these amino acids result in huge numbers of proteins which have a variety of functions.
Natural selection! In the theory of natural selection, those with less beneficial traits won't live to reproduce, but those with beneficial traits will be able to reproduce and pass on those traits to their offspring, which significantly increases the frequency of those beneficial traits.
the (drug and control) are the variable that you will change throught the conducted investigation.