Many of us might say the main goal of staying alive is just that: not dying. As stupidly obvious as this seems, it isn't necessarily true. Zoom in to the level of molecules and cells in any living creature, and you will see quite a different picture from the world we're all used to living in.
Perhaps one of the most interesting aspects of this world is called "apoptosis," or programmed cell death. Essentially, this is a process by which cells in the body intentionally disassemble and decompose themselves. It's a kind of cell suicide.
Granted, this can be brought about by many different factors, both intrinsic and extrinsic to the cell. Generally speaking, it involves a signaling molecule to bind to receptors in the cell, often called "death receptors" (and you thought science was all sunshine and rainbows). Once this happens, a cascade of chemical pathways is initiated, resulting in the cleavage of key structural components and the cessation of cell growth factors. Sounds complicated? It is:
While it is possible for toxic substances to induce apoptosis in a bad way, it is generally believed that this is an essential and useful process for the brain to carry out. Apoptosis is useful in controlling the growth of many areas in the body, preventing tissue from becoming cancerous. It's also necessary in fetal development and the immune system response.
Apoptosis is a fascinating process, and yet another reminder of the delicate balance that must be maintained in every living organism. While we're moving about our lives, decidedly focused on not dying, there are armies of cells in a constant flux of life and death. After all, you can't make an omelette without breaking any eggs.