I'm sure I have written here before about Caenorhabditis elegans, a tiny worm -- about the size of this letter i (without the dot) -- that has become one of the most thoroughly studied animals in biology. Its habits are humble. It is nonpathogenic, noninfectious. It breeds prodigiously. It is transparent. It can be frozen and thawed alive. And heaven knows what else makes it the darling of the wormologists..
More than anything else, it is about a simple an organism as you can find with a nervous system. C. elegans (of the dominant hermaphrodite variety; there are also a few males to enliven the mix) has just 959 cells, which have been individually mapped, exactly the same from worm to worm. Think of that! Less than a thousand cells and it eats, defecates, wiggles from place to place, lays eggs, and otherwise lives a rather full and robust life. Contrast that with the tens of trillions of cells in the human body.
More. C. elegan's genome programs not 959 cells, but 1090. Of these, 131 are slated in advance to die, rather like the cells that die between the webbed digits of a human embryo to give us our useful fingers. Apoptosis, it's called. Programmed cell death. The 2002 Nobel Prize in physiology went to Sydney Brenner, Robert Horvitz and John Sulston for their work on programmed cell death in C. elegans. Tens of billions of cells in our own bodies die each day by apoptosis. We are dying all the time, in bits and pieces. Death is always with us, holding hands with life, hitchhiking in our genome. Whispering in our ear: "I'm here." Nibble, nibble. Waiting, waiting, for the full feast, the final meal.