We breathe because each and every cell in the body requires oxygen to create energy so it can accomplish its work. We breathe to move outside air into the lungs, and into the lungs’ tiny sacs called alveoli, where oxygen is transferred into the bloodstream and where carbon dioxide is transferred from the bloodstream into the air for disposal back out into the surrounding air. This process of breathing is called ventilation, whereas the cellular-level oxidative process of using the oxygen is properly called respiration.
Before the evolution of many-celled organisms with thick bodies, there was no need for ventilation because every cell was adjacent to the air and could transfer oxygen and carbon dioxide directly with the outside air. But in order for larger, thicker organisms to emerge, there had to be a new mechanism for supplying the cells with this gas exchange. The development of lungs and heart and blood– the entire respiratory and cardio-vascular systems– was to solve this ‘engineering problem.’
I don’t know if this has been substantiated by research, but I like to imagine that our breathing, especially its rhythmic movements, express their origin in the rhythmic swimming movements of fishes and jellyfish. The swimming movement accomplishes two things at once: the creature propels itself forward through the water while forcing water across the gill surfaces. The gills are the fish equivalent of our lungs; as water moves over the surface of either one, oxygen and carbon dioxide are tranferred between the creature and the water (or air). Watch a video of a jellyfish swimming, it seems perfectly obvious that our breathing movement originated long before any creature crawled up onto land.
Our breathing, therefore, links each one of us not only to every other breathing person alive today, every other homo sapiens on the planet, it also makes each one of us a member of the breathing community comprised of each and every creature that breathes.
Now that’s what I call a breathing community!