Well, this blog isn't about your heart beats or how you breathe per se. It about the enlightening you with other subtle life-facts. I was never a biology student; so there is a good change you won't find hardcore biology stuff out here.
But I am, through my knowledge of evolution and natural selection, going to try explaining why your heart beats, or why you breathe.
Then again breathing isn't unique to the human species! Fishes breathe under water. Granted, their biological process is different, but biologically they aid in a process called respiration. So do all insects. So by that analogy, they all "breathe".
The essence is in realizing that a simple phenomenon such as "breathing" is very common on the face of earth, and I am just trying to explain why so.