This week at our local Toastmaster’s meeting the word of the day was bumfuzzled. The challenge is to use it as much as possible that night. As I struggled to give my two minute “Table Topic” an impromptu presentation about the paint color Tart Green – it was enough just to try and tell an entertaining story let alone work in a new word. But, as I write about epigenetics I can say without artifice that I am truly bumfuzzled.
Thanks to genomics, we know that we are not solely the product of our genes but also of nature and nurture (and increasingly a whole slew of bacteria, viruses and who knows what else – but that’s another story). Epigenetics, altered gene expression caused by an environmental influence is a part of this new understanding. In this context, the nature and nurture environment can include stress, temperature, nutrition, even toxic chemicals. All of which have been shown, under certain conditions, to reach right in and jiggle the genetic code – causing certain genes to be turned on, or off.
Just as silent pauses in music influence how we hear a song or melody, genes too can be either silenced or turned on to great effect. What’s more, some epigenetic changes don’t just influence the expression of our own DNA, but can influence our children’s and our grandchildren’s gene expression. This is pretty wild if you think about it. There are several ways this can happen. One way is for molecular tags (methyl groups) to be added to the DNA, like pins in a clock timer – telling DNA when to turn off.
An increasing body of literature suggests that epigenetic influences may last a generation or two or even more depending on the species (in some plants epigenetic tags may stick for several generations). For example studies are showing that a grandparent’s nutritional experience can influence their grandchildren’s health; possibly through epigenetic changes. Biologically, and hypothetically, this sort of makes sense. If you have been struggling to make that Saber Tooth stew stretch, it may be a good thing to produce metabolically thrifty descendants. But some toxic chemicals too can influence subsequent generations;not only the grandchildren but the great grands as well. Granted these studies to date have used concentrations of chemicals not relevant in the real world – but they certainly are suggestive. Could we inadvertently be jiggling the DNA of future generations with our modern day chemicals?
Where will this take us? I think about all the Yodels and Ding Dongs that I consumed back in the day, combining a sugar high with poor nutrition and quite possibly toxic chemicals. What if they influence future generations? Is this why my daughter craves an all white diet? What of her kids? Its enough to make one shudder. This is purely hypothetical of course. Scientists have not linked Ding Dongs to disease in grandchildren – though I wouldn’t be all that surprised if they did.
But you see where I’m going. Epigenetics raises fascinating questions. And in the context of my current project (rapid evolution in a chemical world), one in particular looms large. Are epigenetic changes relevant to evolution? And can they be caused by environmental exposures to industrial age chemicals? If my diet influences my grandchildren and perhaps beyond –could my generation’s poor choices from diet, to climate change to toxic chemicals – influence human evolution?
There certainly is quite a bit of excitement about the prospect. Here are biologists David Crews and Andrea Gore writing about the topic: “Epigenetics is the next epoch in evolutionary theory, as these mechanisms alter heritability and force us to confront classical genetic ways of viewing the environment.” Psychology Today ran this headline, A Revolution in Evolution: a return to Lamarck? While others get excited that Some Evolution May Not Depend on Genes. When it comes to evolution, it’s like Epigenetics is the new Black!
Yet as fascinating as many of these studies are, until we know more about the process we ought to proceed with some caution.
Think about it. One some level, it could certainly be beneficial to have this kind of genetic flexibility. Say if I were to move to the arctic wouldn’t it be great if my kids or grand kids were better adapted than I? Maybe stouter bodies or a little more insulation — they’d surely be grateful. But what if my kid decided southern Florida was more to her liking. So she moves there and starts a family. Would her kids be mal-adapted, thanks to me? Of course assuming there is still enough juice to power up the A/C in ten or fifteen years, the grand kids will survive. But consider the plight of wilder animals. While the ability to survive dramatic temperature shifts is a good thing – permanent change in response to temperature in an unpredictable world isn’t. Here is evolutionary biologist Jerry Coyne:
…if the DNA code changed unpredictably back and forth each generation, natural selection and evolution wouldn’t work. Second, there are also epigenetic changes that are induced not by the DNA sequence but by the environment. Temperature, starvation, and other environmental factors can cause methylation of the DNA as well. The thing is, though, that such changes, because they’re rarely passed on to future generations, cannot serve as the basis of evolutionary change. Such changes constitute true Lamarckian inheritance, i.e., the inheritance of acquired characteristics.
And lots of studies show us that Lamarckian inheritance doesn’t operate. Changes that are induced by the environment, or the organism’s “striving,” can’t somehow get incorporated into the DNA.…. My conclusion: if epigenetic changes are involved in an evolutionary adaptation, they must be coded for in the DNA rather than acquired from the environment alone…
So…. those Ding Dongs those of us of a certain age consumed in high school? Clearly not a great choice. But, even if they were to leave behind epigenetic marks influencing the health of my children’s children let’s hope that Coyne has it right. That they won’t change the course of human evolution; we’re leaving enough of a mess behind as it is, we don’t need to be messing with their genetic inheritance as well.