Final answer:
The principle that 'All cells come from pre-existing cells' is part of the cell theory, which is a fundamental concept in biology and is a part of cell theory.
Step-by-step explanation:
The principle that states "All cells come from pre-existing cells" is part of the cell theory. This foundational concept in biology acknowledges that all living organisms are composed of cells, that the cell is the basic unit of life, and that all living cells arise from other living cells through the process of cell division. This was a significant development in biological science, and no evidence has refuted this aspect of the cell theory.