Among the most astonishing revelations in biology was the discovery that all visible living creatures are themselves made up of living "creatures" called cells. Cells are not merely inert structural units or building blocks, but individual beings with lives of their own - living, reproducing, and dying just as we do. We are, in a sense, hives of cells. We move, eat, and speak thanks to the coordinated effort of specialized groups of individuals within our cellular community.

Cells are small. Caenorhabditis elegans, a worm so small it can barely be seen, is made of precisely 969 of them. You are made of an astronomical 5 trillion cells, give or take a few. Obviously, an aggregate that large requires an extraordinary degree of communication and cooperation. Cells must continuously "talk" to each other. They use electrical and chemical signals to control every action you take.

In community, cells organize themselves into specific patterns, maintaining their three-dimensional relationships with great precision. Two separated heart cells pulsating at different rates will, if placed side by side, fall into synchronus rhythm. Cells from different tissues will, if mixed in a blender, re-sort themselves into their original tissues is a short time.

	Throughout evolution, the more cells tended to stick together, the more information they shared. Slowly, the rudimentary systems of primitive single cells became connected and elaborated on, ushering in higher-level behavior such as seeing, feeling, and thinking.
Consider a face: Its basic features change very little in the course of a year. Yet in that time, most of its original cells and all of the molecules of which those cells are made will be replaced by new ones. The fabric changes, but not the pattern.

All material copyright © 1995 Times Books/Random House