The queue structure is one of my own ideas. It is possible that it has been done before, but I did not check. There does not seem to be a lot of research on this topic. That being said, it is a nice toy problem to explore genetic algorithms and diversity.

Regarding the stack approach, I would suspect that new genetic information would immediately be lost since a new organism dies before having much chance to produce offspring. In the off chance it manages to produce offspring, those offspring would also be lost almost immediately since they get popped first.

If you are really curious, you can change line 163 in vivarium.cpp from a pop_front() to a pop_back() to see what happens.