Advantageous traits aren't retained in the population, they're lost because we're just averaging the two best solutions over and over with a little bit of noise. 

population 50, don't keep best creatures, mutation rate 4% - somehow the creatures don't evolve. would debug logic but short on time. 

chunk, multipoint mutation.

Ah, seems that the population disappears? Within 20 generations, no matter what the population size is, all of them disappear and mutations stop being introduced because it's just the same organism over and over.

This time, not even generation 10 and the population is all gone. This was a population with "keep best ones" OFF, and 1% mutation rate. Population disappears, set mutation to 100% - you can see that the fitness will not change, no mutations happen, because somehow the population is 0.