Your comments are a mischaracterization. Suppose for the sake of argument that no humans could digest pasta. But someone came along and invented pasta to see if we could eat it for food. The people that tried to eat only pasta quickly became malnurished and had to go back to eating other things or died. Suppose later we found some humans that could only survive on pasta. Their bodies could not digest anything else. We then discover a genetic difference that is unique to them and makes them only able to digest pasta. We find that they have three additional amino acids that nobody else has for example, that allows for the metabolism of pasta.
This example illustrates how a change in an environment combined with mutations to create diversity within a population can create something entirely new and unique.
It illustrates just one way in how evolution works.