Friday, September 30, 2016

Extending evolutionary theory? - Sonia Sultan

I will be attending the Royal Society Meeting on New trends in evolutionary biology: biological, philosophical and social science perspectives. I'll post each of the abstracts and ask for your help in deciding what question to pose to the speakers. Here's the abstract for Sonia Sultan's talk on Developmental plasticity: re-conceiving the genotype.

For several decades, the phenotype of an organism (i.e, its traits and behaviour) has been studied as the outcome of developmental ‘instructions’ coded in its DNA. According to this model, each genotype is expressed as a specific phenotype; individual differences in fitness-related traits are seen to arise from this stably inherited internal information. This simplified view of development provides the foundation for a Modern Synthesis approach to adaptive evolution as a sorting process among genetic variants. As developmental biologists are aware, however, an organism’s phenotype is not strictly pre-determined by its genotype, but rather takes shape through the interplay of genetic factors with the organism’s environmental conditions. By means of this developmental plasticity, a given genotype may express different phenotypes under different environmental conditions. Accordingly, the genotype can be understood as a repertoire of potential developmental outcomes or norm of reaction.

Re-conceiving the genotype as an environmental response repertoire rather than a fixed developmental programme leads to three critical insights, as illustrated by norm of reaction data from Polygonum plants. Plastic responses to specific conditions often comprise functionally appropriate trait adjustments, resulting in an individual-level, developmental mode of adaptive variation. Environmental responses can extend across generations via effects on progeny growth and fitness, a form of inherited yet non-genetic adaptation. Finally, because genotypes are differently expressed depending on the environment, the genetic diversity available to natural selection is itself environmentally contingent.
Here's a possible question ...
Back in the 1960s we learned that transcription of the lac operon in E. coli was regulated by the environment. This regulation, activation or repression, was passed on to daughter cells as the cells divided. Why didn't this discovery lead to a major revision of evolutionary theory?

6 comments :

  1. The lac operon is a great example. If you wanted to use a human example you could point to tanning as a response to UV induced DNA damage from the environment. The discovery of this mechanism in humans didn't require a rewrite of the Modern Synthesis. Why?

    Fetal alcohol syndrome is suspected to be the result of epigenetic changes. If epigenetic changes can result in maladaptive phenotypes, then how can it be called an adaptive process?

    Ultimately, phenotype plasticity is a result of DNA sequence. The predictable response to a given environmental stimulus is controlled by sequence specific function. In order to get a different response to a specific stimulus you have to have a change in the underlying DNA sequence. How is this not exactly what the Modern Synthesis already states?

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  2. Larry wrote:

    "...........but rather takes shape through the interplay of genetic factors with the organism’s environmental conditions. "

    Not only genetic factors. But, very important and actually, essential:

    epigenetic factors. I have posted the list here several times.

    If these are not taken into consideration, the revision will not mirror and incorporate the new achievements and knowledge of various labs around the globe.

    At the topic " Where do complex organisms come from ", i have posted a list, which imho probably by far does not mention all mechanisms that determine body form and shape.

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    1. Perhaps you can clear something up for me, Otangelo: Why do some ID creationists get so excited about the idea of epigenetics? How would this increase the likelihood that life was created by God?

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    2. What determines which DNA bases are methylated in response to environmental stimuli?

      Like lutesuite, I really have to wonder why ID/creationists get in a lather over epigenetics. Perhaps they latch on to the idea that epigenetics somehow falsifies the theory of evolution which feeds into their God of the Gaps argument for ID.

      In the end, almost all of the methylation patterns in cells are wiped out during the process of gamete production. What little DNA methylation does make it through has very little impact on the resulting phenotype with respect to the differences between species. You may get fatter mice due to epigenetic factors, but you don't get cats from mice. The only explanation for the differences between divergent species is differences in DNA sequence, not epigenetics.

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  3. Back in the 1940s, Waddington offered a theory of "canalization" in development. Why was this considered such a major revision in evolutionary theory that it was summarily rejected by orthodox defenders of the synthesis?

    It seems to me that ideas about epigenetics, Baldwin effects, and canalization are ideas in the second tier - not as important as the first tier ideas about selection and heritability, but at least important as the other major cluster of second tier ideas: those dealing with sympatry and allopatry.

    So call it a minor revision of evolutionary theory.

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