On the Other Hand… Epigenetic Changes May Have Less Effect On Evolution Than We Think
September 22, 2011 Leave a comment
I love this: I posted a TED talk about the potent future of genetic sequencing in medicine, then posted an article about the importance of epigenetic changes in a model plant, and made an offhanded comment about how that reined in my enthusiasm about the TED talk. Now Science Daily brings us an article from researchers who’ve monitored epigenetic changes in that same model plant over the course of several generations, and found that while the epigenome changes rapidly, those changes don’t necessarily stick – so they’re not necessarily an important factor in evolution, or at least not as important as that last article would’ve had you believe.
Why do I love this? Because, in a sense, it’s science at its best: constantly re-evaluating and self-correcting. Clearly Science Daily had no problem juxtaposing these articles within a few days of each other, because it’s not its agenda to push one view or another (as far as we can tell, anyway); just to advertise the truth, or rather the closest thing we have to it.
I also love it for my own educational value, because suddenly I was like “Wait – I just swallowed that last article uncritically. Now I feel kind of silly.” The thing is, individual scientific findings are rarely interesting on their own – they’re interesting in terms of the implications and applications, which is why any of these articles will probably have less to say about the actual study conducted than about what the researcher thinks this means for the future. And this latter part, unfortunately, will always be conjecture. We’ll just have to absorb and move along with the actual findings, and try not to get too attached to the hypothetical implications 🙂
Jean-Baptiste Lamarck would have been delighted: geneticists no longer dismiss out of hand his belief that acquired traits can be passed on to offspring. When Darwin published his book on evolution, Lamarck’s theory of transformation went onto the ash heap of history. But in the last decade, we have learned that the environment can after all leave traces in the genomes of animals and plants, in form of so-called epigenetic modifications…
Using Arabidopsis, the workhorse of modern plant genetics, the researchers determined how often and where in the genome epigenetic modifications occur — and how often they disappear again. They found that epigenetic changes are many orders of magnitude more frequent than conventional DNA mutations, but also often short lived. They are therefore probably much less important for long-term evolution than previously thought.
A team led by Detlef Weigel, director of the Department for Molecular Biology, focused on one of the most important epigenetic marks, methylation of DNA. Tiny chemical building blocks, methyl groups, are thereby attached to individual letters of the DNA, mostly to cytosines. The genetic information itself in form of the four different letters or nucleotides that make up the genetic code remains unchanged in this process…
“Our experiments show that methylation changes are often reversible.” In other words: New epimutations are often not maintained over the long term. “Only when selection wins out over reversion can these epimutations affect evolution,” says Hagmann. A new epimutation thus must have a strong evolutionary advantage so that it can become established before being lost again. Because reverse mutations do not necessarily happen in the next generation, it is still possible that epigenetic differences contribute to inheritance of traits between parents and their children or grandparents and their grandchildren…
What makes epigenetics interesting for human health is the fact that some epigenetic changes can be triggered by external factors. There is evidence that nutrition or the bond between children and their parents can leave traces in the genome that can be passed on to the next generation. The limited stability of DNA methylation implies, however, that such differences do not necessarily last forever, which is probably not a bad idea because a famine might not last forever. It also means that altered DNA methylation often cannot become subject to natural selection.
I wonder if epigenetics will ever take as prominent a role in students’ education as genetics? I don’t think I ever heard of an “epigenetics class” in university… Quick, to the future!