Macroevolutionary freezing and the janusian nature of evolvability: Is the evolution (of profound biological novelty) going to end?
In a macroevolutionary timescale, evolvability itself evolves. Lineages are
sorted based on their ability to generate adaptive novelties, which leads to the optimization
of their genotype-phenotype map. The system of translation of genetic or
epigenetic changes to the phenotype may reach significant horizontal and vertical
complexity, and may even exhibit certain aspects of learning behaviour. This continuously
evolving semiotic system probably enables the origin of complex yet functional
and internally compatible adaptations. However, it also has a second, Bdarker^, side. As
was pointed out by several authors, the same process gradually reduces the probability
of the origination of significant evolutionary novelties. In a similar way to the evolution
of societies, teachings, or languages, in which the growing number of internal linkages
gradually solidifies their overall structure and the structure or interpretation of their
constitutive elements, the evolutionary potential of lineages decreases during biological
evolution. Possible adaptations become limited to small Bperipheral^ modifications.
According to the Frozen Evolution theory, some of the proximate causes of this
Bmacroevolutionary freezing^ are more pronounced or present exclusively in sexual
lineages. Sorting based on the highest (remaining) evolvability probably leads to the
establishment of certain structural features of complex organisms, e.g. the modular
character of their development and morphology. However, modules also Bmacroevolutionary
freeze^ whereas the hypothetical Bthawing^ of modules or their novel adaptive
combinations becomes rarer and rarer. Some possible ways out of this dead end include
the rearrangement of individual development, e.g. neoteny, radical simplification, i.e.
sacculinization, and transition to a higher level of organization, e.g. symbiosis or symbiogenesis. The evolution of evolvability is essentially a biosemiotic process situated
at the intersection of the genocentric modern synthesis and the evo-devo-centric
extended synthesis. Therefore, evolvability may eventually connect these three not
necessarily contradictory approaches.