We breath, secretes, sweats, release in and or out things that our body needs and does not need and because of that, we are able to move, fly, walk, talk, laugh, run, swim naturally. These reactions have become weight effecting. Weight is that factor that speeds, accelerate, and decelerate our natural landing, distances, total area, ability and control of our surroundings e.g. Ongoro flies hundreds of kilometres than ladet because their weight mature later in time compared to ladet wherefore, their bodies contain enough energy to move them supper distance. Animals e.g. human, the four legged, and two legged with short wings e.g. penguins etc mainly are created to move. Things that makes them interesting is how they move/walk compared to those that flies. Moving livings swift directions because they jump, sit, sleep, run forwards and backwards, sideways. Flying livings however, do all moving can do but not backwards. Fish swimming is by far the most interesting compared to all of the above because it does all livings e.g zigzag, forward, up, down, and around do at their highest speed. Also we need to remember is that things that do not move/fly backwards, comes to standstill at that stage it can move backward by strength of water current or wind. Human are created the way they are because they are logically dangerous to all other things that are like them or around them, but are created creative hence they learned their opponents and have so forth replicated them and in a good way become teacher, helper, healer etc to them in whatever way possible.
Note: There are so many theories that talks about the above. None of them is used to explain this.