Frozen plasticity is a hypothesis in evolutionary biology based on punctuated equilibria and augmenting it with a mechanism for species stability based on evolutionarily stable strategies on the gene and allele level. Evolutionary biology is a sub-field of Biology concerned with the origin of Species from a Common descent, and Descent of species Punctuated equilibrium is a theory of evolutionary biology which states that most sexually reproducing populations experience little change for most of their geological In Game theory and Behavioural ecology, an evolutionarily stable strategy (ESS is a strategy which if adopted by a population of players History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance An allele (ˈæliːl (UK /əˈliːl/ (US (from the Greek αλληλος allelos, meaning each other) is one member of a pair or series of different forms
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Mechanism
Mature species
In a mature species, many genes have several alleles and the alleles of different genes interact in a complex web of epistatic interactions. Epistasis is the Interaction between genes Epistasis takes place when the action of one Gene is modified by one or several other genes which are sometimes called Most traits are codetermined by a large number of genes, many of which contribute in various degrees to different traits. In sexually-reproducing species, only 50% of these will be passed on to a descendant, with the other 50% coming from the other parent. As such, the selfish gene cannot be simply selfish; it is participating in a large number of games against other genes, one game per generation, and many of the solutions will be mixed evolutionarily stable strategies, corresponding to particular frequencies of different alleles. In Game theory and Behavioural ecology, an evolutionarily stable strategy (ESS is a strategy which if adopted by a population of players An allele (ˈæliːl (UK /əˈliːl/ (US (from the Greek αλληλος allelos, meaning each other) is one member of a pair or series of different forms
As with the Hawk-Dove game, if we apply artificial selective pressure, the frequencies will shift; however, as soon as the pressure is removed, the game will return to its natural equilibrium. The game of Chicken, also known as the Hawk-Dove or Snowdrift game is an influential model of conflict for two players in Game theory.
Similarly, if a new mutant allele arises (and is not immediately eliminated), the frequencies of the various existing alleles may shift, but the nature of the equilibrium is unlikely to be significantly changed.
Speciation and evolution through natural selection
Peripatric speciation (or another event which leaves a small number of individuals genetically isolated) reduces genetic variability through the founder effect and further through subsequent genetic drift. Peripatric speciation is a form of Speciation, the formation of new Species through Evolution. In Population genetics, the founder effect refers to the loss of genetic variation when a new colony is established by a very small number of individuals from a larger In Population genetics, genetic drift is the accumulation of random events that change the makeup of a gene pool slightly but often compound over time This makes the group genetically plastic, but too small for natural selection to work.
When the number of individuals grows, natural selection takes over. Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of Because of the low genetic variability, a mutation has a good chance that it will "mean the same thing" in offspring. There are fewer other genes that could adjust to compensate for its effects. The species can evolve new adaptations to its environment.
Eventually, as mutations pile up, the amount of genetic variability grows to the point that plasticity is frozen and the new species is fixed.
Note that this process is not necessarily successful every time; it may take many tries before it produces a daughter species rather than a dying colony.
Sexual vs Asexual species and gradualism
This mechanism only works for sexual species. Frozen plasticity would therefore expect that while sexual species evolve in punctuated equilibria, asexual species undergo gradualistic evolution. Punctuated equilibrium is a theory of evolutionary biology which states that most sexually reproducing populations experience little change for most of their geological Phyletic gradualism is a macroevolutionary Hypothesis rooted in uniformitarianism.
Microevolution and Macroevolution
A mature sexual species retains the ability to respond to selective pressure by adjusting the frequencies of the various alleles within the already present genetic variability - microevolution. Microevolution is the occurrence of small-scale changes in Allele frequencies in a population over a few generations also known as change at or below the Species
Advantage of sex
Not only is microevolution much faster than asexual evolution, it is much more robust against temporary fluctuations. When the fluctuation passes, the species can swiftly return to the norm.
The capability for microevolution is therefore an important advantage of sex.
Experiments
Most experimentation and breeding experience is with microevolution; typically we see elasticity - as soon as the experimenter or breeder relaxes the pressure, the species will tend toward its natural form.
In addition, artificial selection is usually conducted with species and lines known to have been derived from a small number of individuals (which would tend to plasticity) or which have been successfully domesticated (which may mean that they were plastic at the time) or both. As such, they may not be representative of species in nature.
See also
References
Flegr, J. Punctuated equilibrium is a theory of evolutionary biology which states that most sexually reproducing populations experience little change for most of their geological In Game theory and Behavioural ecology, an evolutionarily stable strategy (ESS is a strategy which if adopted by a population of players , On the "Origin" of natural selection by means of speciation, Rivista di Biologia / Biology Forum 91 (1998) 291-304 [1]
Encyclopedia of Life Support Systems (EOLSS), Al Gobaisi D. and Badran A. (eds), UNESCO, Eolss Publishers, Oxford,UK
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