Reply to comment

Well, I thought it would be fun to take on a project that seems a little over-ambitious.  However, I don't expect to make a model that I can point to and say, "Look, that's evolution."  I'm starting with the basic necessaries of an evolving system:

• A population of critters
• with a certain 'trait' (sight distance)
• which reproduce, passing on their trait value to their children, with slight variations.

I also wanted a good way to visualize the distribution of trait values in the population over time.  This setup successfully demonstrated an important idea about evolution (which Paul Grobstein pointed out)- evolution can occur without any selective pressure, due to variations within a population and the left-wall effect.  The next step was to see if I could introduce some form of selective pressure and see its effects on the population.  For this, I:

•  Introduced 'predators'
• which could eat members of the 'prey' population,
• BUT the prey could sense the presence of predators when they came within a certain distance related to the prey's trait value (sight distance)
• on sensing a predator nearby, the prey would run away

Over time, the prey population 'evolved;' those prey with higher trait values were more likely to survive and reproduce, passing on their trait value (with variation) to their offspring.  This created a trend toward a population with a larger mean trait value over time (check out the model here).  From there I wanted to add another trait, controlling the prey's 'field of vision,' which I did and which showed a similar trend in the presence of predators (mean field of vision steadily increased up to a complete circle).  This model is not yet on Serendip but can be seen here.

From that point, I have gone in several directions without seeming to make any particular headway.  I tried giving predators some traits which would affect how good they were at catching prey, with more successful predators having a better chance of reproducing and passing on their trait values.  I also played with several more traits for prey (mostly controlling their response on sensing the presence of a predator), all of which showed basically the same pattern over time as the existing traits, and didn't get me anywhere particularly new and interesting.  Additional ideas I have come up with but not really tried to incorporate yet include:

• Creating a more varied landscape, which could introduce new complexities into the evolutionary process.  This could include some 'resources' the critters need, affect both predator and prey's sight ability (and maybe encourage 'hiding' or 'sneaking' behavior).
• Making some traits to control group dynamics- how prey and predators interact with their kind 
• Somehow generalizing the trait creation process such that I don't have to create a specific trait and name how it will vary and how it will affect behaviors, but let turtles discover traits for themselves and surprise me with some ingenuity or mis-ingenuity.

I would welcome any ideas, suggestions, questions, or challenges, and look forward to seeing what other people are working on and where they are.  Go team!