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."

Most red grapefruit today descend from mutations born of gamma ray exposure. In a 1950s "Atoms for Peace" experiment, radioactive material was placed in a garden with plants around it. Those at the right distance mutated from pink into today's red, sweeter variety.

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.

In 1907, biologist Henry Van Peters Wilson pushed a sponge through silk mesh into loose cells. They regrouped in seawater and regrew into a sponge. Later experiments mixing two species found that cells sorted by species and formed separate sponges.