Where in my body is the original cell from which I was formed?
Category: Biology Published: October 25, 2013
By: Christopher S. Baird, author of The Top 50 Science Questions with Surprising Answers and Associate Professor of Physics at West Texas A&M University
From one point of view, the original cell you came from (the fertilized egg cell) was destroyed long before your body was formed. From another point of view, every cell in your body is the original. In either case, there is not just one original cell sitting in your elbow or toe that can be identified as the ancestor of all your other cells. Let us look at the mechanics of cell reproduction to make sense of this.
Two cells are formed from one cell through the process of cell division. In cell division, the DNA within a cell is replicated. The two copies of the DNA are then separated into two different cell nuclei. The cell then splits into two pieces, each piece containing its own set of DNA. In this way, two identical cells are now sitting where one used to be. You can't really identify one of the new cells as the "original cell" and the other cell as a mere copy, because the process is symmetric. Don't think of cell division as a builder constructing a new house patterned after his old house. Cell division is more like a builder cutting his old house in half and turning each half into a self-contained house. You can't really identity one of the new houses as the original house. They are both part of the original house. At the same time, they both aren't, because the original house was destroyed when you cut it in half. The case is similar with cell division.
You began life as a single cell. You became a fully-functioning, independent human after many cell divisions turned that first cell into the trillions of cells that make up your body. In a strict sense, that first cell was destroyed when it underwent the very first cell division. But the essence of the first cell, your DNA, was given to both daughter cells in the process of cell division. The essence of who you are continued to be passed along with each cell division, until all the trillions of your cells had been completed. From a philosophical perspective, the original cell lives on in all of your cells.
Note that even if the first cell had not been destroyed during cell division, it would have still been destroyed eventually through the normal wear and tear of life. Almost all of your cells die within a few days to a few years, depending on where they are in the body. Your cells are in a constant state of dieing and being replaced by new cells. As a result, very few of the cells in your body now are the exact same cells that you had 20 years ago. According to a study done by the Karolinska Institute in Stockholm, outer gut cells die after a few days, outer skin cells die after two weeks, red blood cells last four months, liver cells last a year, and bone cells last about a decade.