In an attempt to explain the uniqueness of the coding mechanism of living c
ells as contrasted with the multispecies structure of ecosystems we examine
two models of individuals with some replicative properties. In the first m
odel the system generically remains in a multispecies state. Even though fo
r some of these species the replicative probability is very high, they are
unable to invade the system. In the second model, in which the death rate d
epends on the type of the species, the system relatively quickly reaches a
single-species state and fluctuations might at most bring it to yet another
single-species state.