This section will briefly describe part of the creatures that appeared, fought for life, and died in this digital jungle. As we will see, most of the adaptations brought by evolution are adaptations to the other creatures present in the soup, rather than adaptations to the very simple environment created by Tierra.
At the beginning was the ancestor. It was 80-instruction long, and endlessly replicated itself in memory. As it began filling the soup, it became a new resource of the environment. Some new creatures appeared in memory, a mutation having robbed them of part of their code. But the information they needed to reproduce was all around them, in the code of the "normal" creatures.
The first parasites were born. Because they were only
half as long as the ancestor, they only needed half the time to reproduce.
They were much faster. And they quickly invaded the soup.
However, they could not survive without their hosts because they needed
part of the code in the host in order to reproduce. Every time they began
dominating the soup, running the hosts to extinction, they died as quickly
as they had come, starved for information.
Their dying allowed some breathing space for the hosts, which were able
to reproduce again, thus adding to the soup the information needed by the
parasite. This led to a stable oscillation between a soup dominated by
parasites and a soup dominated by hosts.
This stability was short-lived. Hosts evolved ways to
protect themselves from parasites, and parasites evolved ways to circumvent
these protections.
This evolutionary race stopped when a new species of hosts appeared. These
hosts had learned how to use the parasites to boost their reproduction,
by tricking them into replicating their hosts. Because the tricky hosts
had a complete genome, they did not really need another creature to help
them reproduce. They simply got a bonus every time a parasite tried to
use them. They were untouchable, and they invaded the world. After a while,
they were the only thing left in the world.
Being alone in the soup, they evolved into social creatures,
and became inter-dependent. The new creatures could only reproduce when
gathered into clusters of close relatives. This cooperation implied trust,
and shortly after cooperation appeared, a new brand of parasites evolved.
These cheaters inserted themselves into a cluster of related creatures,
and "when the trust was passed to them, they violated it"
([7]).
They used a mechanism similar to the one the tricky hosts had evolved,
and tricked the social creatures into replicating their parasites.
A new evolutionary race had begun...
Along the way of evolution, some creatures had discovered sex. When Tom Ray tried to turn off mutation to stop evolution for a while and observe the different creatures, evolution kept going. The creatures were mingling parts of their genome to create offspring with a code different from their parents. Evolution was under way and unstoppable...