Did you know that all around the world, more people are overweight than ever before in the Earth's history? This is partly because of the way we eat, partly because of the way we live, and it's also partly because of the types of bodies our parents passed on to us. A long time ago, children and grownups were active every day, just doing all the jobs that needed to be done to stay alive. Food was sometimes scarce, and so people who could store fat were more likely to stay alive. Today, though, grownups and children don't move around nearly as much as they once did. Food is almost always plentiful. And our bodies' ability to store weight now means that we easily become overweight. It's a complicated problem!