  Recently, Adami and coworkers have been able to measure the information
content of digital organisms living in their {\em Avida} artificial life
system. They show that over time, the organisms behave like Maxwell's demon,
accreting information (or complexity) as they evolve. In {\em Avida} the
organisms don't interact with each other, merely reproduce at a particular rate
(their fitness), and attempt to evaluate an externally given arithmetic
function in order win bonus fitness points. Measuring the information content
of a digital organism is essentially a process of counting the number of
genotypes that give rise to the same phenotype.
  Whilst Avidan organisms have a particularly simple phenotype, Tierran
organisms interact with each other, giving rise to an ecology of phenotypes. In
this paper, I discuss techniques for comparing pairs of Tierran organisms to
determine if they are phenotypically equivalent. I then discuss a method for
computing an estimate of the number of phenotypically equivalent genotypes that
is more accurate than the ``hot site'' estimate used by Adami's group. Finally,
I report on an experimental analysis of a Tierra run.
