Your Blood Cells Are Ancient Time Travelers From 700 Million Years Ago

Scientists discovered that the cells floating around in your blood are super distant relatives of the tiniest living things that existed 700 million years ago! By studying how blood cells evolved, they found out that your immune system [the body's defense team] grew from some of the first life forms that ever lived on Earth. Pretty wild to think that inside you right now are descendants of creatures so ancient that dinosaurs hadn't even shown up yet!