This is just an interesting article about the general role of epigenetics in humans. Epigenetics seems to assure a level of randomness and changeability unavailable in our genetic codes, further complicating our efforts to find the “blueprint” for any individual.
By allowing genes to be switched on or off, epigenetics allows the environment, both external and internal to the body, to change the expression of our individual genetic code.
This gives us hope to alter some of how our bodies are genetically programmed to act through subtle changes in our biochemistry, and also assures a level of randomness unavailable in our genetic code. And this further complicates our efforts to find a firm “blueprint” for any individual.
The unifying theme for much of modern biology is based on Charles Darwin’s theory of evolution, the process of natural selection by which nature selects the fittest, best-adapted organisms to reproduce, multiply and survive.
The process is also called adaptation, and traits most likely to help an individual survive are considered adaptive. As organisms change and new variants thrive, species emerge and evolve.
over the past century, advances in genetics and molecular biology have outlined a modern, neo-Darwinian theory of how evolution works: DNA sequences randomly mutate, and organisms with the specific sequences best adapted to the environment multiply and prevail. Those are the species that dominate a niche, until the environment changes and the engine of evolution fires up again.
But this explanation for evolution turns out to be incomplete, suggesting that other molecular mechanisms also play a role in how species evolve. One problem with Darwin’s theory is that, while species do evolve more adaptive traits (called phenotypes by biologists), the rate of random DNA sequence mutation turns out to be too slow to explain many of the changes observed.
The rapid emergence of trait variety is difficult to explain just through classic genetics and neo-Darwinian theory
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? And why do just a low percentage (often less than 1 per cent) of those with many specific diseases share a common genetic mutation?
Lamarck’s theory, long relegated to the dustbin of science, held, among other things, ‘that the environment can directly alter traits, which are then inherited by generations to come’.
The question is this: if natural selection isn’t acting on genetic mutations alone, then what molecular forces create the full suite of variation in traits required for natural selection to finish the job?
One clue came almost a century after Darwin proposed his theory, in 1953, just as James Watson and Francis Crick were unravelling the mysteries of DNA and the double helix. In that year, the developmental biologist Conrad Waddington of the University of Edinburgh reported that fruit flies exposed to outside chemical stimulus or changes in temperature during embryonic development could be pushed to develop varying wing structures. The changes the scientists induced in that single generation would, thereafter, be inherited by progeny down the lineage. Waddington coined a modern term – ‘epigenetics’ – to describe this phenomenon of rapid change.
the single-generation change in the fruit-fly wings were supportive of the original ideas of the heretic Lamarck. It appeared that the environment could directly impact traits.
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.
Today, that is the precise definition of epigenetics: the molecular factors that regulate how DNA functions and what genes are turned on or off, independent of the DNA sequence itself.
Epigenetics involves a number of molecular processes that can dramatically influence the activity of the genome without altering the sequence of DNA in the genes themselves.
One of the most common such processes is ‘DNA methylation’, in which molecular components called methyl groups (made of methane) attach to DNA, turning genes on or off, and regulating the level of gene expression.
Environmental factors such as temperature or emotional stress have been shown to alter DNA methylation, and these changes can be permanently programmed and inherited over generations – a process known as epigenetic transgenerational inheritance
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.
But epigenetic inheritance does not follow many of the Mendelian rules that apply to classic genetics and the neo-Darwinian theory of evolution.
Epigenetic transgenerational inheritance, by contrast, occurs when the germline (sperm or egg) transmits epigenetic information between generations, even in the absence of continued direct environmental exposure
a number of studies have indicated that environmental stress can promote epigenetic alterations that are transmitted to and induce pathologies in subsequent generations
Several studies now support the role of environmental stress in promoting the epigenetic transgenerational inheritance of disease.
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
In mammals with longer generation times, we have found toxicant-induced abnormal traits propagated for nearly 10 generations.
In most of these studies, the transgenerational traits do not degenerate but continue.
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.
Support for an epigenetic role in evolution continues to mount
Nearly all types of genetic mutations are known to have a precursor epigenetic change that increases the susceptibility to develop that mutation. We observed that direct environmental exposure in the first generation had epigenetic changes and no genetic mutations but, transgenerationally, an increase in genetic mutations was identified.
Since environmental epigenetics can promote both trait variation and mutations, it accelerates the engine of evolution in a way that Darwinian mechanisms alone cannot.
Generations of scientists and the public have been taught genetics, but few have been exposed to the relatively new science of epigenetics – in fact, inclusion of epigenetics into the molecular elements of biology and evolution has been met with opposition.
Author: Michael Skinner is a professor of biological science at Washington State University