Yesterday I played around with the repo and found that (IIUC) one "environmental condition" already present in the simulation is the mutation rate. With relatively low mutation rates, I find that a whole tape filled with `<` is a good "substrate," in the sense that it can sit there stably for a long time until a random mutation puts `,` into one of its cells. Within a few generations, it will have spattered copies of the substrate into all its neighbors. Then they sit until a random mutation puts `,` into one of their cells... and so on.

I described what (I think) I'm seeing in https://github.com/Rabrg/artificial-life/pull/1 , and suggested in https://github.com/Rabrg/artificial-life/pull/3 that random mutations ought to blow away the whole tape rather than modify only one cell of it. However, even with that modification to the rules, I still see the `<` substrate taking over the whole map, except when the mutation rate is very high. (I admit this doesn't make a ton of sense to me.)

So, anyway, it's easy to make the mutation rate vary from one side of the map to the other. If you do that right, you can see the `<` substrate take over the low-mutation-rate side of the map, but fail to take over the higher-mutation-rate side.

The `<` substrate is easy to see in the gif: it's a rapidly spreading splotch of red with gold noise flickering inside.