Oh wow - I haven't thought of Tierra in 25 years. There was a time in the early 90's where I was super fascinated by genetic algorithms, artificial life, and chaos theory. I think it was all kicked off by James Gleick's Chaos and following threads in the bibliography.

I think Tierra was featured in Steven Levy's book Artifical Life.

In another thread on HN, people are talking about where programmers of the 90's thought we were headed and your mention of Tierra reminds me that I thought artificial life was going to be a big, big deal.