μείωσις

The Greek word meiosis (μείωσις) means 'lessening' or 'reduction'—from meioun, 'to lessen.' When J.B. Farmer and J.E.S. Moore observed egg and sperm cells under the microscope in 1905, they noticed these cells had half the chromosomes of normal cells. The number of chromosomes was reduced by half. Hence: meiosis.

This was the solution to a puzzle that had confused biologists for decades. If sperm and egg each have the full complement of chromosomes, and they fuse to make an embryo, then the embryo should have twice as many chromosomes as its parents. But it doesn't. Something must be cutting the number in half before fertilization.

That something is meiosis—a special kind of cell division that occurs only in reproductive tissues. It's like mitosis, but with a difference: the paired chromosomes separate so each new cell gets only one copy of each chromosome. Two divisions instead of one. The name was perfect: the number of chromosomes is literally lessened.

Without meiosis, all sexually reproducing life would collapse within one generation. Your children would inherit twice your chromosomes, your grandchildren four times, and by the tenth generation, a cell would be larger than a human. Every organism that makes sperm or eggs depends on meiosis to halve the chromosome number. We owe our existence to a process named after the one thing it does: make the number smaller.