We are all fish

In another round of being amazed by science discussed in a recent series of videos from Hank Green, I’m fully on board with the idea that — genetically, biologically, technically — we are all fish, except for the animals that aren’t fish. Basically, you, me, cats, dogs, birds, lizards and even whales — yes, whales — are fish.

Going back hundreds of millions of years, every land-dwelling, air-breathing animal is a descendant of a common ancestor that was a fish — and by fish, of course, we mean water-dwelling animals with bones. Which, by extension, makes a shark not a fish because they don’t have skeletons — they have cartilage.

Wait, so humans, horses and hawks are more closely related to a brook trout than the brook trout is to a shark or a starfish or an octopus? Yes, because it turns out many of the fish we think of as fish have lungs and hands and skeletons — they just don’t look like ours. And by extension, we’re still fish because we and the dinosaurs and woolly mammoths and dodos evolved to have skin to hold our 70% watery body inside. We never left the water — we brought the ocean with us.