Emergence by Steven Johnson

Pop science book about emergent behavior, fun factoids follow:

If the slime cells pumped out enough cyclic AMP, clusters of cells would start to form. Cells would begin following trails created by other cells, creating a positive feedback loop that encouranged more cells to join the cluster. If each solo cell was simply releasing cyclic AMP based on its own local assessment of the general conditions, Keller and Segel argued in a paper published in 1969, then the larger slime mold community might well be able to aggregate based on global changes in the environment ...
I would give seminars to biologists, and they'd say, "So?, Where's the founder cell? Where's the pacemaker?' It didn't provide any satisfaction to them whatsoever." Indeed, the pacemaker hypothesis would continue as the reigning model for another decade, until a series of experiments convincingly proved that the slime mold cells were organizing from below.
-- page 16
Look at what actually happened here: they've (harvester ants) built the cemetery at exactly the point that's furthest away from the colony. And the midden is even more interesting: they've put it at precisely the point that maximizes its distance from both the colony and the cemetery. It's like there's a rule they're following: put the dead ants as far away as possible, and put the midden as far away as possible without putting it near the dead ants.
-- page 33
The town itself is peculiarly built, so that someone can live in it for years and travel into it and out of it daily without ever coming into contact with a working-class quarter or even with workers...
I know perfectly well that this deceitful manner of building (rich over here, poor over there) is more or less common to all big cities. I know as well that shopkeepers must in the nature of the business take premises on the main thoroughfares. I know in such streets there are more good houses than bad ones, and that the value of land is higher in their immediate vicinity than in neighborhoods that lie at a distance from them. But at the same time I have never come across so systematic a seclusion of the working class from the main streets as in Manchester...
And yet it is precisely Manchester that has been built less according to a plan and less within the limitations of official regulations -- and indeed more through accident -- than any other town.
Friedrich Engels, page 37
More is different. This old slogan of complexity theory actually has two meanings that are relevant to our ant colonies. First, the statistical nature of ant interaction demands that there be a critical mass of ants for colony to make intelligent assessments of its global state.
(it) also applies to the distinction between micromotives and macrobehaviour: individual ants don't "know" that they're prioritizing pathways between different food source when they lay down a pheromone gradient near a pile of nutritions seeds.
Ignorance is useful. The simplicity of the ant language -- and the relative stupidity of the individual ants -- is, as the computer programmers say, a feature not a bug.
Encourage random encounters. Decentralized systems such as ant colonies rely heavily on the random interactions of ants exploring a given space without any predefined orders.
Look for patterns in the signs. While the ants don't need an extensive vocabulary and are incapable of syntactical formulations, they do rely heavily on patterns in the semiochemicals they detect.
Pay attention to your neighbors. ... You can restate it as "local information can lead to global wisdom."
pages 78-79
(post-medieval cities expanded due to) First, the heavy wheeled plow, which tapped the muscular energy of domesticated animals, arrived with the German invaders, then swept through the river valleys north of the Loire; at roughly the same time, European farmers adopted triennial field rotation, which increased land productivity by at least a third. Capturing more energy from the soil mean that larger population densities could be maintained. As larger towns began to form, another soil-based technology became commonplace, one that was even more environmentally friendly: recycling the waste products generated by town residents in the form of crop fertilizer...
The result is a positive feedback loop: the plow and the crop rotation makes better soil, which supplies enough energy to sustain towns, which generate enough fertilizer to make better soil, which generates enough energy to sustain even larger towns.
page 112