logo4 Evolution is progress—                          
progress is creativity.        
home button home active button book button book active button wiki button wiki active button cladogram button cladogram active button blog button blog active button contact button contact active button about button about active button

Latest Blog Entries

Recapitulation Rule

Adaptability Rule

Property/Behavior Rule

Moral

Morality

< January 2012 >
MonTueWedThuFriSatSun
      1
2345678
9101112131415
16171819202122
23242526272829
3031     
 vline

Genetic Assimilation

Genetic Assimilation is an evolutionary concept developed by Conrad Hal Waddington. It is explains with Darwinian principles how acquired characters become inheritable. Probably because of his leftist political views his ideas never became widely accepted.

General confusion

On genetic assimilation exists a not so instructive instructive wikipedia page. I didn't read the original publication. I have no access. I found many quotations that leave the matter more or less dubious.

Among those who tried to summarize it is Mary Jane West-Eberhard[1],

"
Genetic assimilation treated environmentally induced traits as polygenic threshold traits, which could spread if positive selection lowered the threshold for their expression.
"

Jonathan M W Slack [2], and

"
This is a Darwinian mechanism that mimics the inheritance of acquired characters. ... His key idea was that a qualitative morphological change can be produced by an external treatment, but the competence to respond to the treatment is a quantitative variable that depends on many loci. If the treatment is applied, and a proportion of individuals show the morphological effect, then selective breeding from this group can eventually produce a population in which the morphological change arises spontaneously without the treatment.
"

Christian Braendle and Thomas Flatt [3].

"
Genetic assimilation is the evolutionary process by which a phenotype produced specifically in response to some environmental stimulus, such as a stressor, becomes stably expressed independently of the evoking environmental effect. How does this process of assimilation work? \\ **First**, in the absence of an environmental stimulus, a particular threshold trait is stably expressed, and phenotypic deviants remain cryptic because the environmental threshold for their expression is too high. \\ **Second**, in the presence of an environmental stimulus, previously cryptic genetic variation for the threshold trait is uncovered and the threshold for the expression of deviant phenotypes not seen under normal conditions is lowered. \\ **Third**, selection in the presence of the environmental factor enriches the previously cryptic alleles determining the trait. \\ **Eventually**, these alleles become so frequent that the expression of the trait overcomes the higher threshold in the absence of the environmental stimulus. Thus, genetic assimilation transforms an environmentally induced (phenotypically plastic) trait into a phenotype which is stably expressed without the eliciting environmental stimulus: the genetically assimilated phenotype is no longer plastic, but exhibits a genetically fixed response independent of the environmental conditions, a phenomenon called canalization.
"

If anyone can make something reasonable out of it, I can't. Therefore let's start with the phenomenon Waddington tried to explain.

[Error: Macro 'include' doesn't exist]

References

1. Mary Jane West-Eberhard, Toward a Modern Revival of Darwin’s Theory of Evolutionary Novelty, Philosophy of Science 75, Nr. 5 (Dezember 1, 2008): 899-908.
2. Jonathan M W Slack, Conrad Hal Waddington: the last Renaissance biologist?, Nature Reviews. Genetics 3, Nr. 11 (November 2002): 889-895.
3. Christian Braendle and Thomas Flatt, A role for genetic accommodation in evolution?, BioEssays 28, no. 9 (September 1, 2006): 868-873.

Genetic Accomodation

Genetic accommodation is a concept of evolution introduced by Mary Jane West-Eberhard[1,2]. According to Braendle and Flatt[3], genetic accommodation is a generalization of the concept of genetic assimilation. Although I cannot uncritically follow their explanation, I agree as from fauceir perspective the scope of genetic accommodation includes one more fauceir. In that sense. genetic accommodation is one more step up the ladder towards Fauceir Theory.

General Confusion

Evolutionary Novelties & Latent Capacities

The Concept of genetic accommodation tries to explain evolutionary novelties by latent capacities. An evolutionary novelty is defined

"
a discrete phenotypic trait that is new in composition or context of expression relative to established ancestral traits.
"

Such an approach raises more questions than it answers. Which are in particular:

  1. Can we really call a trait a novelty if its capacity is latently present already?
  2. But most of all, how does the latent capacity evolve?

Many species bear the capacity to exhibit different phenotypes such as in metamorphosis and temperature dependent sex determination [4]. From these example we can learn that not the phenotype itself but the capacity do show it under appropriate circumstances is a target of evolution.

A this point I refuse to discuss the various hues of the theory. I understand so many authors offering so many modified definitions as an indicator that none of these concepts really meets our data sufficiently. That's time to introduce Fauceir Theory.

References

1. Mary Jane West-Eberhard, Developmental Plasticity and Evolution, 1. Aufl. (Oxford University Press, USA, 2003).
2. .
3. Christian Braendle und Thomas Flatt, „A role for genetic accommodation in evolution?“, BioEssays: News and Reviews in Molecular, Cellular and Developmental Biology 28, Nr. 9 (September 2006): 868-873.
4. Neuwald, Jennifer L, und Nicole Valenzuela. „The lesser known challenge of climate change: thermal variance and sex-reversal in vertebrates with temperature-dependent sex determination“. PloS One 6, Nr. 3 (2011): e18117.
 
   

(c) Mato Nagel, Weißwasser 2004-2024, Disclaimer