Life

There isn't one perfect definition of 'alive,' but most living things share a few habits. They take in stuff from outside to keep going (you eat). They keep themselves organized and don't just fall apart (your body fixes itself, mostly). They grow. They make copies of themselves. The copies are a little different each time, so over many, many generations, living things slowly change. Everything alive on Earth — every tree, ant, fish, person, awkward houseplant — shares the same basic chemistry, which suggests we all came from a single starting point about three and a half billion years ago. We are, structurally speaking, one giant family with very loud cousins.