  The problem of evolutionary complexification of life is considered one of the
fundamental aspects in contemporary evolutionary theory. Parasitism is
ubiquitous, inevitable, and arises as soon as the first replicators appear,
even during the prebiotic stages of evolution. Both in theoretical approaches
(computer modeling and analysis) and in real experiments (replication of
biological macromolecules), parasitic processes emerge almost immediately. An
effective way to avoid the elimination of the host-parasite system is through
compartmentalization. In both theory and experiments, the pressure of
parasitism leads to the complexification of the host-parasite system into a
network of cooperative replicators and their parasites. Parasites have the
ability to create niches for new replicators. The co-evolutionary arms race
between defense systems and counter-defense mechanisms among parasites and
hosts can progress for a considerable duration, involving multiple stages, if
not indefinitely.
