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Glad to have Anne's (and anyone else's) thoughts, as an aid to my further thinking about how I presented the simulation, about the simulation itself, and about biological evolution.  To wit ....
What is being simulated is not all of biological evolution but only a particular set of features of biological evolution.  In particular, sexual reproduction has been left out of the simulation altogether.  Also left out are the existence of several copies of the same gene ("diploidy") as well as any other characteristics that create a distinction between genotype (what genes are present in a given organism) and phenotype (the appearance of an organism), and any related mechanisms that enhance phenotypic diversity ("recombination") or reduce it ("chromosomal organization").  In the simulation there are only two genes, phenotype is a direct and simple consequence of genotype, and organisms reproduce individually rather than by interaction with other individuals. The point of the simulation is not to replicate the entirely complexity of biological evolution but rather to show that some features of it (a tendency to increasing diversity, and a dynamic interaction between that and differential reproductive success yielding adaptation to selection pressures) can be accounted for without any of the features of biological evolution other than "descent with variation," and differential reproductive success.  This needs to be made clearer in my presentation of the simulation.  And I need to give further consideration to the issue of whether the points the simulation illustrates will necessarily continue to hold if additional features of biological evolution are added to the simulation.  
Clearly, I also need to be clearer about the "visual representation."  I forget that people tend to see displays like the one in the simulation in terms of spatial location.  What's represented is not at all spatial location, what is instead represented is "phenotypic" space, the space of all possible organisms with two phenotypic characteristics with one (perhaps height) corresponding to location on the y-axis and the other (perhaps weight) corresponding to location on the x-axis.  When the population of organisms in this space is less scattered, it is of lower diversity.  When it is more scattered, it is of higher diversity.  Over time, the population samples more and more of the space.  Its not that "the space was getting bigger" but rather that the space having been explored by the population gets bigger.
Yes, I also need to make it clearer that the issue the simulation addresses  is "not "why change occurs," but rather where increasing diversity comes from."  To put it slightly differently, the simulation shows that a particular kind of directional change, increasing diversity, can occur in the absence of any kind of selection or other influence from anything outside the "descent with variation" system and without any kind of directionality in the individual entities exhibiting descent with variation.   Even when all the offspring of all entities are fully randomly distributed, and all entities are equally likely to reproduce, the population as a whole moves from exhibiting lower diversity to exhibiting higher diversity.  Adding "natural selection" doesn't change this; it only keeps the population from displaying the maximal diversity of which it is capable. 
All of this is not intended to answer the general question of where change comes from but instead to make it clear that directed change can occur as a result of undirected change even in the absence of an external director of any kind (ie "natural selection").  And to motivate the suggestion that some form of undirected change, an inherent randomness in all things (From random motion to order), may actually be the underpinnings of all directed change.  The key idea here is that undirected change may be the starting point rather than something that requires explanation (Making sense of the world: the need to entertain the inconceivable).  And that all directed change needs to be thought of from that starting point.    
Glad to have the issue of a "biological imperative" raised, for future consideration in the course (and elsewhere).  Yes, I think there is an important distinction to be made between directed change in biological evolution and that involving "conscious intention", and we'll develop that idea more as we talk about cultural and individual evolution.  Is there something comparable to "unconscious drives" operating in biological evolution? in the simulation?  Yes, probably in both.  And in cosmic evolution as well, so I'm not sure I'd call it a "biological imperative."  And that-whatever-it-is, in any case, is quite different from what humans experience/think of as "intention."  In particular, there is in the simulation, and probably in biological evolution for the most part, nothing corresponding to a representation of a place-to-be-gotten-to, any sense of an objective to be achieved.