Narwhals, the unicorns of the sea, have survived for a million years with low genetic diversity — a trait that usually suggests a species is close to extinction. But a recent survey found narwhals number in the hundreds of thousands, countering the assumption that lots of gene variants within a population are necessary for survival.

“There’s this notion that in order to survive and be resilient to changes, you need to have high genetic diversity, but then you have this species that for th