Commensalism is the term you are looking for
<u>Explanation:</u><u> </u>
In general, field of study refers to gaining the knowledge in a particular branch. On the other hand, science means the system where we can attain the knowledge about the universe. This always delivers with theoretical and experimental descriptions in a detailed manner about natural phenomenon.
This handles with each and every aspects about living organisms and environment. This paves the way to know more details in particular part. Hence, field of study like physics, engineering also referred a science in this manner.
The term that can be used to describe evolution by natural selection is SCIENTIFIC THEORY.
Theory means "the best explanation so far."
Scientific theory is a work in progress. It is a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method, and repeatedly confirmed through observation and experimentation.
I think it might be lyosomes as they help break down waste and other stuff in a cell.