How do human tissues react to the passage of time? How much of my anatomy has stayed intact? If I weighed six kilos at birth and at present weigh several times that, what parts of my original body have remained? What parts have formed along the way?
When I look at my foot I do not think of a foot that is sixteen years old, as the entity I know of as “me” is, but rather a foot that has morphed into several incarnations over the last sixteen years. The foot of my newborn self was one eighth of my current foot. Nail, skin, bone, red blood cells have reproduced, died and been cast off into the surrounding medium. 30 liters of water, several dozen kilograms of carbon, oxygen, hydrogen, nitrogen, a few grams of salt, chlorine, iron – we know what it takes to make a human being! Gestation is the process by which elements are assembled, following guidelines and utilizing tools impossible to replicate artificially. This is nature’s trump card, leg up, ace in the hole. A body in the process of formation is perfect. How long does a body exist before it begins to decay?
Red blood cells develop from committed stem cells in bone marrow. They are in circulation for an estimated 120 days before dying off. The cells lining a stomach last a maximum of two days. Granulocytes, a variety of white blood cell, the stuff that keeps you alive on a daily basis, have a lifespan ranging from 10 hours to a few days. Macrophages eat the dead cells, and they in turn are eaten by other macrophages, once their 16 days of programmed service are up. The cellular lipids and membranes of a neuron are continuously renewed, bone cells are kept alive by satellite cells.
How long before my first body has shed itself away completely? When I look at myself, I see a life form in various stages of degeneration, several identical reincarnations extending from each other. In the mirror, I can pull back my sleeves to reveal scar tissue on my shoulder, the pink melding into the surrounding reddish-brown skin, the stretch marks on my stomach, the small grey freckle just beneath my nose. Sometimes I wake up and the soles of my feet will have hardened a bit, or a line on my skin will have diminished somewhere, or my stomach, kidneys, head will feel lighter. Though, logically, I am dying always, I prefer to think of it as being brand-new always. This is both a termination and a continuation.