Final answer:
Rudolf Virchow, in 1858, proposed that cells only come from other cells, which is now a key concept in cell theory.
Step-by-step explanation:
The early scientist who proposed that cells arise only from preexisting cells by a process of division was Rudolf Virchow. In 1858, Virchow developed the hypothesis that all cells come from other cells, a foundational concept for the cell theory. This idea was a critical advance in biology, providing a clear understanding of how cells reproduce and how continuous growth and development occurs in living organisms. His proposal was concisely expressed in the Latin phrase 'omnis cellula a cellula', meaning 'all cells arise from cells'.