These replicating systems could not, individually, grow beyond N, but Eigen was able to prove that things would be different for systems that contained different types of RNA. If the cycles of X individual systems could be combined into a single complex cycle – that Eigen called hypercycle – one would have a supersystem of XN monomers that would maintain the same replication potential of the individual systems. Eigen proposed therefore that the formation of hypercycles was the mechanism by which primitive replicating systems could increase the number of their components, and therefore their own complexity.
In 1981, however, Ursula Niesert proved that things are not at all that simple, because hypercycles too are under threat, and risk to be swept away by at least three new types of catastrophes. An hypercycle can be destroyed by a selfish RNA that replicates faster without giving any contribution to the system (the selfish gene catastrophe). It can furthermore be destroyed by a mutant that skips one or more steps, and makes the hypercycle progressively shorter until it degenerates into a simple cycle (the short-circuit catastrophe). And finally it has been demontrated that an hypercycle with more than four cycles is intrinsically unstable and spontaneously tends to degenerate (the population collapse catastrophe). As anyone can see, hypercycles do not guarantee that primitive RNAs had a realistic probability of going on replicating themselves for millions of years. Primitive RNAs, in conclusion, could certainly behave both as genes and enzymes, but this does not save the replication paradigm, because it cannot avoid the various catastrophes that necessarily affect all replicators.

Eigen’s paradox

In 1981, Manfred Eigen proposed that the first replicators would have had a greater chance of surviving if they had been housed into small compartments instead of being freely diffusing in a solution. This because compartments have an individuality, and individuals are the units on which natural selection can operate.