Bottom-up To Humanity III - Atoms

We use the word atom to designate an aggregation of neutrons, protons, and electrons which form a stable structure. They have become common because, by definition, stable structures tend to survive longer than unstable structures.
This stability is very convenient for us as observers. We can trust that within certain conditions atoms behave in well-known ways, allowing us to abstract much of the hidden complexity. In fact, there's nothing new here - pretty much the same happened when we considered protons, neutrons and electrons as basic units.

I was just trying to find a nice explanation for the origin of atoms when I found the The History of Evolution page at the Principia Cybernetica Web. Looks interesting, but it didn't have the details I needed though.