  We twice modify the Penna model for biological ageing. First we introduce
back (good) mutations and a memory for them into the model. It allows us to
observe an improvement of the species fitness over long time scales as well as
punctuated equilibrium. Second we adopt a food/space competition factor that
depends on the number of accumulated mutations in the individuals genomes, and
get rid of the fixed limiting number of allowed mutations. Besides reproducing
the main results of the standard model, we also observe a mortality maximum for
the oldest old.
