Every living thing, it turns out, is built from the same basic unit
Botanist Matthias Schleiden and physiologist Theodor Schwann compared notes in 1838 and realized plant and animal tissue were both made of cells, proposing the cell as the basic unit of all life. Two decades later Rudolf Virchow closed the last gap by showing cells don't spontaneously form: every cell comes from a pre-existing cell dividing.