Cell

Textbooks taught for decades that bacteria outnumber human cells 10 to 1 — a 1972 rough estimate cited without scrutiny. A 2016 Weizmann study found about 38 trillion gut microbes vs. 30 trillion human cells: 1.3 to 1, not 10 to 1. The number was inflated tenfold.

If more cells mean higher cancer risk, whales and elephants should constantly get cancer. Yet they rarely do—less often than smaller animals. This contradictory phenomenon is called "Peto's paradox."

Taller people have higher cancer rates. More cells mean more cell divisions, and more divisions mean more opportunities for mutations to occur.