If our genes and cells arose randomly through competition for supremacy, then how can we explain so many wonderful processes where cells are programmed to sacrifice themselves for the good of the whole, especially during development?
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Find Out More To date, science offers no real definition for life, but from our human experience, nothing defines life better than death. Yet drawing the line between life and death can get quite interesting. For instance, the mere absence of life is not death—after all, rocks are not “dead.”
The Gift of Life—From a Single Cell Life is always a gift from one being to another, like an eternal flame that is passed along from one generation to the next. However feeble the flame may be, at least one is needed to light others, and they, in turn, light some more. And so it goes on; there is no spontaneous combustion. The over 7 billion life candles we see in the world today bear the flame that God first kindled in Adam and Eve some 6,000 years ago.
Among humans and many animals and plants, the continuity of life involves two gametes (or sex cells, namely sperm and an egg) coming together and forming a single fertilized egg. Remarkably this new cell in a human is so tiny that we can observe it only under a microscope. The wonder of this new life is even more staggering when we perceive that an “Ashley” or a “David,” a future singer or plumber or president, arises from that single cell.
This special cell divides over and over again, until it becomes the 100 trillion or so cells that characterize an adult human. The trillions of cells somehow come together at defined points to form beautiful symmetry with mind-boggling, nano-scale precision.
What if the two sides of the nose failed to meet midway? Instead of a puddle or scar face, what usually forms on every one of our faces is something that even the great master artists can only dream of capturing.
Both the unicellular zygote and the trillions of adult cells have life, but this life exists apart from the individual cells. During development, cells often “die,” but life remains.
The Necessity of “Cell Death” to Build Our Bodies
Indeed, many cells must purposefully sacrifice themselves for the good of the whole body, a marvelous testimony to the Creator’s hand. For example, some serve as scaffolds, supporting the emergence of more permanent and specialized cells. In the wake of each new organ is a fast-disappearing trail of cells—cells that must “die” by design.1 This process is appropriately termed programmed cell death (PCD).
The clean-up and removal of the scaffolds is far from a random process. Thus a grand orchestration of cell death sculpts organs and organ systems; and as the baby grows to maturity, trillions of cells are lost, eliminated by this precisely controlled process. Amazingly, the immune system remains silent while the body gradually loses several persons worth of cells!
In an adult, when any one of these trillions of cells turns rogue, the self- destruct button in that cell is frantically triggered (the programmed cell death tool kit is present in all cells with nuclei). When the self-destruct machinery fails, just one rogue cell can—as a spreading cancer—threaten the life of the whole organism.
Note: PCD should not be confused with a better-known process called necrosis. Necrosis usually involves the uncontrolled demise of cells in response to external forces, such as heat or trauma. Necrosis is an ugly affair, characterized by the breakdown of the cell membrane, loss of energy, swollen organelles (tiny parts of the cell—like mitochondria), and the dumping of cell contents into the outside environment, thereby provoking the body’s immune response. The surrounding region may also suffer scarring.
The PCD machinery in cells can sometimes be hijacked by certain viruses and cancer cells. Some viruses and cancers halt programmed cell death so they can proliferate unchecked in the undying cell.
Other viruses, such as HIV, are harmful because they trigger programmed cell death in certain immune cells that normally fight off pathogens. In particular, they attack the white blood cells known as helper T cells, thereby compromising the body’s immune system and opening the body to numerous secondary infections.
Death Programs Cells have several different ways to bring about their own demise, with fancy names such as apoptosis, autophagy, anoikis, and excitotoxity. The details are complicated, but an example or two will help illustrate their crucial role during development and adult life.
Our skin must constantly produce and replenish a tough layer of outer armor, made of “dead” skin cells (beauty is skin deep!). These cells die by producing a protein called keratin, which eventually chokes off the cell (keratin is the tough but flexible material in your fingernails and hair). This particular form of cell death is called cornification. Another example of programmed cell death is the removal of the webbing that exists between fingers during fetal life; and this process is called apoptosis.
Formation of the Eye Let’s consider the role of programmed cell death in sculpting just one organ, the eye.2
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