Part of understanding the goals of science is to realize that the questions we ask may never be answered, maybe because there is no answer. In one of my current classes we had a discussion about whether or not science can answer everything and the truth is that it cannot. At least not in today's world. Nothing can be proven 100% because we cannot test every single object on this earth to see if it fits our hypothesis. For many of our categories there are exceptions, for instance the Platypus is considered a mammal even though it lays eggs. There will almost always be an exception.
Answer to yesterday's question: It turns out that some amino acids in a protein's primary structure do not matter. As long as what it is changed to is either around the same size and/or polarity, the protein will not be effected. Other amino acids will greatly effect the protein: if it is necessary for a small amino acid to be at a certain spot on the chain and it gets switched out for a larger one, the protein will not be able to work correctly. It all depends on the location, size, and/or polarity.
Today's question is more of a though provoking one. There is no right or wrong answer. Do you think that one day science will have the ability to answer everything?