Mitochondria, the power plants of your cells, were once free-living bacteria. More than 1.5 billion years ago, one was engulfed by another cell without being digested, and the two never parted. Evidence of that past: mitochondria still carry their own DNA, ring-shaped like a bacterium's and passed down only through the mother.
In 2022, a young tagged bar-tailed godwit flew from Alaska to Tasmania in about 11 days of nonstop flight, covering 13,560 km without eating, drinking or landing. Before departure, these birds pile on huge fat reserves and shrink their digestive organs, which are useless during the journey.
To escape rivals, a dung beetle rolls its ball of dung in a straight line. At night, it holds its course using the glowing band of the Milky Way. In a planetarium, researchers showed that beetles rolled straight under a starry sky but wandered aimlessly when the galaxy was switched off. It was the first animal known to navigate this way.