Your whole body came from one cell. The moment your father’s sperm joined your mother’s egg, it formed a single cell with your full DNA inside. That cell then split into two identical copies. Each of those split into two more. And those split, and split, and split - about 50 doublings later - until you had trillions of cells.
The splitting process is called mitosis. Before a cell can divide, it copies all its DNA - about 3 billion letters’ worth. Then the cell aligns the two copies of DNA at its center, pulls them apart toward opposite ends, and pinches itself in half. Each half ends up with one full copy of the DNA, and they’re now two separate cells.
This isn’t just how you grew. It’s how you stay alive. Cells in your skin, gut, blood, and elsewhere are constantly dividing to replace ones that die. You’re producing tens of millions of new cells every minute through mitosis right now. When the process goes wrong - cells dividing when they shouldn’t, or refusing to stop - that’s how cancer starts.
