Frozen plasticity theory
This theory suggests a mechanism of the origin of adaptive traits in sexual organisms. The classical Darwinian mechanism of the origin of adaptive traits by natural selection can explain the evolution of such traits only under a very special situation, e.g., in a genetically homogeneous population of asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in a genetically heterogeneous population of sexual organisms.
The frozen plasticity theory suggests that sexual species can evolve new adaptations by accumulation of random mutations only when their members are genetically uniform, i.e., only after a portion of the population of the original species has split off, balanced on the edge of extinction for several generations, and then undergone rapid expansion. After a short period of time, corresponding to 1-2% of the duration of the species (estimated on the basis of paleontological data), polymorphism accumulates in the gene pool due to frequency-dependent selection; and thus, in each generation, new mutations occur in the presence of different alleles and therefore change their selection coefficients from generation to generation. The species ceases to behave in an evolutionarily plastic manner and becomes evolutionarily elastic on a microevolutionary time-scale and evolutionarily frozen on a macroevolutionary time-scale. It then exists in this state until such changes accumulate in the environment that the species becomes extinct.
The first version of the theory of frozen plasticity was presented in the paper: On the "origin" of natural selection by means of speciation. Flegr J. 1998, Riv Biol -Biol Forum 91:291-304.
Current version of the theory was presented in the papers:Flegr J. 2010: Elastic, not plastic species: Frozen plasticity theory and the origin of adaptive evolution in sexually reproducing organisms. Biology Direct, 5:2..
More recent results related to frozen evolution and frozen plasticity theories:
Flegr, J. 2013: Why Drosophila is not Drosophila any more, why it will be worse and what can be done about it? Zootaxa, 3741(2): 295-300
Toman, J., Flegr, J. 2017: Stability-based sorting: The forgotten process behind (not only) biological evolution. Journal of Theoretical Biology, 435, 29-41. doi.org/10.1016/j.jtbi.2017.09.004
Toman, J., Flegr, J. 2018: Macroevolutionary freezing and the janusian nature of evolvability: Is the evolution (of profound biological novelty) going to end? Biosemiotics, 11: 263-275. https://doi.org/10.1007/s12304-018-9326-y
Toman, J. & Flegr 2018: A virtue made of necessity: Is the increasing hierarchical complexity of sexual clades an inevitable outcome of their declining (macro)evolutionary potential? Evolutionary Biology, 45: 374-394. https://doi.org/10.1007/s11692-018-9462-y.
Flegr, J. & Ponížil, P. 2018: On the importance of being stable – evolutionarily frozen species can win in fluctuating environments. Biological Journal of Linnean Society, 125, 210–220. bly110, https://doi.org/10.1093/biolinnean/bly110
Flegr, J. 2022: Adaptations, By-products, and Spandrels. In The Cambridge Handbook of Evolutionary Perspectives on Sexual Psychology, ed. Shackelford T.K., Cambridge University Press. doi.org/10.1017/9781108943529