Birds migrate. Goats grow their gonads. Squirrels bury themselves. Migration. Reproduction. Hibernation. Seasonal rhythms. We know that every species from single-celled organisms to human beings express intricate daily rhythms — called circadian rhythms. But did you know many species exhibit annual patterns as well? They’re called circannual or seasonal rhythms and have their roots in evolutionary biology. Primarily governed by the length of sunlight …
