Emergence: This is the concept that leads to us using a wiki to to compile, sort and refine knowledge. Science, language and civilization are all the product of emergence. Put simply it is the tendancy for order to emerge out of a large system in small increments that build to a regular pattern. It the case of language this idea is intriguing as it implies that we are, as a group of speakers, creating the language we speak. It does not come from a dictionary, but from common usage. This idea implies that large system emerges from a collective rather than from an authority. It is a bottom-up view of the how the world works rather than a top-down one.
Ants finding food - ants move in random paths in there serach for food and other materials. As they do so they lay down tracks with pheremones that other ants can follow. There are a large number of tracks for any of the next ants to follow but the tracks that lead to a food sourse, say might have get redundant tracks. When there are two tracks the path attracts a few more ants than a single track would. As the track attracts more and more ants, more and more ants make it to the food source.
Flower district in NY, NY - Similarly to the ants, one flower shop opens on a street that people start swerving over to to pick up flowers. If sufficient traffic emerges to this spot other vendors take advantage of the traffic and open more flower shops thereby causing more swerving. If this continues you have a whole district of flower vendors.
Crowd sourcing - One of the first people to describe emergence as a property was a founder of eugenics (name?) who went to a county fair and was intrigued by a carnival game where fair goers would guess the wieght of a bull. He thought that the these "lower class" people would guesses would be well off the mark and he would use this as further evidence of the superiority of the "upper class". What he found when he averaged out all of the guesses however was that they were basicly, collectively right on the money. Most of the individual guesses were way off, but taken as a group they could figure the wieght almost freakishly acurately. The idea that the collective knowledge of a whole group of people is better than the knowlege of an individual eventually lead to websites such as the one you are looking at right now. (I would argue that this is exactly what science is as well.)
Trails - social trails are great example of this concept in action, but even the spine trail or Blakley Ave started out as social trails, then logging roads, then more developed roads....It is entirely possible that any road started out as a game trail.
Common practices - When one part of a lesson goes really well we tell other instructors, some might try it, if it works for them they share with even more people. If the idea works very well the education staff may pass it on to future grad classes. Some of these ideas might turn into lessons and get written down. Some may just become a common pratice (eg. perspective stories are effecting on the canopy tower or E1T1 might be a great way to get students up the Yama Hill)
Argot - using words such as E1T1 or Yama Hill
Source - most of the examples above come from an episode of the radio show/pod cast of RadioLab (www.radiolab.org/2007/aug/14/) which in turn used various other sources.