  The issue of how to create open-ended evolution in an artificial system is
one the open problems in artificial life. This paper examines two of the
factors that have some bearing on this issue, using the Tierra artificial life
system.
  {\em Parsimony pressure} is a tendency to penalise more complex organisms by
the extra cost needed to reproduce longer genotypes, encouraging simplification
to happen. In Tierra, parsimony is controlled by the \verb+SlicePow+ parameter.
When full parsimony is selected, evolution optimises the ancestral organism to
produce extremely simple organisms. With parsimony completely relaxed,
organisms grow larger, but not more complex. They fill up with ``junk''. This
paper looks at scanning a range of \verb+SlicePow+ from 0.9 to 1 to see if
there is an optimal value for generating complexity.
  Tierra (along with most ALife systems) use pseudo random number generators.
Algorithms can never create information, only destroy it. So the total
complexity of the Tierra system is bounded by the initial complexity, implying
that the individual organism complexity is bounded. Biological systems,
however, have plenty of sources of randomness, ultimately dependent on quantum
randomness, so do not have this complexity limit. Sources of real random
numbers exist for computers called {\em entropy gatherers} -- this paper
reports on the effect of changing Tierra's pseudo random number generator for
an entropy gatherer.
