In nature you are suppose to hunt for food and that usually involves chasing after a prey and using energy. But now that all our food is bought, we don't have to do that. It does not mean that we arent supposed to just lay around all day. That's how we get fat.
You need to exercise to keep healthy and yes it is possible to maintain weight without exercise (liposuction, acai berry (if it works), and all those other things) , the best way is to exercise because that gives you many many more benefits than all the other choices of weight loss