I like your example of emergent behavior to build the brick wall but I cannot help but think that while it is an interesting example, it seems to be orchestrated to deliberately build a wall (by specifying a set of steps rather than building a goal-oriented hierarchy) and could thus fail to properly be defined as emergent behaviour. That said, it's not always clear what constitues it and what doesn't. I mean, after all, even the classic wall-following example could be said to be deliberate.