The removal of the cell membrane.
The membrane regulates homeostasis by letting "stuff" (general term) in and out of the cell.
Answer - Theory
Reasoning - Your best bet and term to describe the evolution by natural selection is theory as to still scientific theory/research is still ongoing and changes can be made in a different direction.
Bacteria! Bacteria! Bacteria! :)
A circle is to round as an oval is to elliptical/egglike.