Apoptosis is a programmed system of cellular death or cellular "suicide" in multicellular organisms, which is as essential to the well being of the organism as any of the normal living functions of a cell. Consider our own bodies for instance. Each one of us has millions of cells that make up different organs and which are constantly undergoing division and multiplication. If it were not for the mechanisms of apoptosis in place, the unchecked growth of cells would prevent any single part from working properly - which as we know, is what happens in certain cancers. in fact, the reason why so many of us escape cancer is because the body has a way of recognizing cells with damaged DNA and inducing apoptosis in such cells. It is only when there is some trouble with the detection and elimination system, that cancer actually occurs!
Apoptosis is especially important in the developmental phases of an organism. The proper formation of our fingers and toes for example, requires the death of certain cells during the process of limb and digit formation, while certain connections between neurons (nerve cells) in the developing brain also depends on the apoptosis of specific cells. A common example of a regular apoptosis in an adult human is the sloughing off of the inner lining of the uterus at the start of woman's menstrual cycle.
Exactly what happens in apoptosis? Scientists who have studied this problem have shown that apoptosis may be induced either passively - i.e. due to the shut down of the signals that tell the cell (or cells) what to down under normal circumstances - or because of signals that actively tell the cell to shut down. The shutting down of the cell's normal growth activities, activates certain enzymes, which in turn, degrade various parts of the cell, eventually leading to the fragmentation of DNA (a landmark of apoptosis) and the phagocytosis of the dying cells by other cells in the body.
In 2002, Sydney Brenner, Robert Horvitz and John Sulston, shared the Nobel Prize in Physiology and Medicine for their discoveries that lead to a better understanding of this vital process of apoptosis.