Genome complexity: importance of epigenetics (Introduction)

by David Turell , Friday, March 31, 2017, 16:12 (2794 days ago) @ David Turell

A very supportive new article:

https://aeon.co/essays/on-epigenetics-we-need-both-darwin-s-and-lamarck-s-theories?utm_...

"genetic mutation rates for complex organisms such as humans are dramatically lower than the frequency of change for a host of traits, from adjustments in metabolism to resistance to disease. The rapid emergence of trait variety is difficult to explain  just through classic genetics and neo-Darwinian theory. To quote the prominent evolutionary biologist Jonathan B L Bard, who was paraphrasing T S Eliot: ‘Between the phenotype and genotype falls the shadow.’

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"And the problems with Darwin’s theory extend out of evolutionary science into other areas of biology and biomedicine. For instance, if genetic inheritance determines our traits, then why do identical twins with the same genes generally have different types of diseases? ...How is it that hundreds of environmental contaminants can alter disease onset, but not DNA sequences? In evolution and biomedicine, the rates of phenotypic trait divergence is far more rapid than the rate of genetic variation and mutation – but why?

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"At the start, Lamarck might have been pilloried as a religious heretic, but in modern times, it is the orthodoxy of science – and especially Darwin’s untouchable theory of evolution – that has caused his name to be treated as a joke. Yet by the end of his career, Darwin himself had come around; even without the benefit of molecular biology, he could see that random changes were not fast enough to support his theory in full.

"Lamarck’s – make sense. Indeed, although the vast majority of environmental factors cannot directly alter the molecular sequence of DNA, they do regulate a host of epigenetic mechanisms that regulate how DNA functions – turning the expression of genes up or down, or dictating how proteins, the products of our genes, are expressed in cells.

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"All of these epigenetic mechanisms are critical and have unique roles in the molecular regulation of how DNA functions. The regulation of biology, it follows, will never involve a ‘genetic-only process’, nor an ‘epigenetic-only process’. Instead, the processes of epigenetics and genetics are completely integrated. One does not work without the other.

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"Environmentally induced epigenetic transgenerational inheritance has now been observed in plants, insects, fish, birds, rodents, pigs and humans. It is, therefore, a highly conserved phenomenon. The epigenetic transgenerational inheritance of phenotypic trait variation and disease has been shown to occur across a span of at least 10 generations in most organisms, with the most extensive studies done in plants for hundreds of generations.

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"Much as Lamarck suggested, changes in the environment literally alter our biology. And even in the absence of continued exposure, the altered biology, expressed as traits or in the form of disease, is transmitted from one generation to the next.
The environment plays an essential role in evolution. In a Darwinian sense, it determines which individuals and species will survive through the inexorable engine of natural selection. But a large number of environmental factors can also impact evolution and biology more directly, through epigenetic means: traits can shift through exposures to temperature and light or in response to nutritional parameters such as high fat or caloric restriction diets. A host of chemicals or toxins from plants and the general environment can impact phenotypic variation and health.

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" Although the field of evolution is currently focused on neo-Darwinian genetic concepts, our findings suggest that epigenetics also has a role in the speciation and evolution of Darwin’s finches.

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"Neo-Darwinian and neo-Lamarckian mechanisms both drive evolution, and they appear to be intertwined... Classic neo-Darwinian evolution involves genetic mutation and genetic variation as the main molecular mechanisms generating variation. Add to these mechanisms the phenomenon of environmental epigenetics, which directly increases trait variation, and you enhance the ability of the environment to mediate natural selection and evolution.

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" embracing neo-Lamarckian ideas does nothing to challenge classic neo-Darwinian theory. The accepted sciences are essential and accurate, but part of a bigger, more nuanced story that expands our understanding and integrates all our observations into a cohesive whole. The unified theory explains how the environment can both act to directly influence phenotypic variation and directly facilitate natural selection,

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"A unified theory of evolution should combine both neo-Lamarckian and neo-Darwinian aspects to expand our understanding of how environment impacts evolution. The contributions of Lamarck more than 200 years ago should not be discounted because of Darwin, but instead integrated to generate a more impactful and insightful theory. Likewise, genetics and epigenetics must not be seen as conflicting areas, but instead, integrated to provide a broader repertoire of molecular factors to explain how life is controlled."

Comment: Very supportive of Lamarck