If you read my blog regularly you know that issue of how genes and environment interact to produce traits is a topic near and dear to my heart. Generally the media misrepresent this subject as “nature versus nurture”, and even many scientists fail to properly explain modern scientific understanding in this area.
When I learned that the The Leonard Lopate Show on WNYC was going to run a feature on “Epigenetics“, I was hoping for a nice clear exposition. After all, understanding epigenetics is one way to rid one’s mind of the useless dualistic way of thinking that allows people to argue whether a trait is caused by genes (so-called “nature”) or environment (so-called “nurture”). Epigenetics is the study of modifications to genes that do not involve sequence changes. If for some reason the sequence of the genetic code is altered, we can clearly call this a “genetic change”. Sometimes that change is even brought on by some environmental cause — mutagenic forms of energy or chemicals frequently alter our gametic DNA — but such changes still should be labeled “genetic” because their main consequence is a change in the genetic code passed on to offspring. But what if some environmental change occurs that alters how the gene functions without actually changing the gene sequence? This is the realm of epigenetics, where the environment and genes mingle to produce inheritance factors that cannot be fully accounted for by genes alone. The best-understood form of epigenetic effect is methylation, where a chemical modification to DNA can change the way a particular gene is expressed. What makes methylation interesting is that it can effect the way genes passed on to offspring are expressed: we don’t just inherit genes from our parents but also the methylation pattern left by our parents (also referred to as “genetic imprinting”). Epigenetics makes the question of “nature or nuture?” a bit muddy, as the environment affects how a gene is expressed.
In this segment Lopate interviewed Richard C. Francis, author of a new book on epigenetics. Francis gave a pretty clear definition of epigenetics, although I wonder if listeners with no education in genetics would fully grasp his explanation. He went on to explain a number of studies that suggested that environmental conditions experienced by parents could affect how the genes they pass on to children (or even grandchildren) are expressed. His primary example was of Dutch children who experienced in-utero famine and later were more likely to be obese, suggesting that maternal environment produced the epigenetic inheritance of a more ‘thrifty’ metabolism. Francis also suggested that folic acid might be over-prescribed to mothers and could be the ‘missing cause’ of increased levels of autism; although this would be a remarkable example of epigenetic effects, it remains mostly conjecture.
By far the best part of this interview was the suggestion that epigenetics in part vindicate the oft-mocked Lamarck, who suggested that acquired traits could be passed on to offspring. Maternal and paternal epigenetic effects can arise from environmental influences, so to call them “acquired traits” makes sense.
Despite this one nice point, this was not the most shining example of clear scientific journalism. As I have discussed before, Leonard Lopate’s lack of basic biological understanding often leads to a lot of confusion, and Francis did a poor job of correcting the Lopate gaffs. For instance, Lopate suggested that “the body rejects most mutations”, a statement that is really hard to make sense of without more information. Is he talking about the process by which our immune system kills off mutant cells? Or is he mistaking the process of natural selection against deleterious mutations between generations for being a “within the individual” process? Francis let this all slide, missing a chance to clarify and educate. Lopate also betrayed on several occasions his outdated dualistic thinking, asserting that over-eating could have “no genetic effect at all” (as if you can eat without somehow employing any gene products). Again here was a nice chance missed to explain the difference between ‘no meaningful genetic variations related to differences in propensity to over-eat’ and ‘no genetic effect on our eating patterns’. Beyond missing chances to correct his host’s misstatements, Francis also created his own forms of confusion. In discussing the post-traumatic stress disorder (PTSD) effects that are found in the children or grandchildren of trauma victims, Francis made the strong suggestion that “inherited PTSD” is an epigenetic phenomenon. But an equally viable hypothesis is that the behavior of PTSD parents leads them to raise their children in a manner that leads to “inherited PTSD” — that cultural inheritance rather than epigenetic inheritance is to blame — and this alternative was not even offered to the listener. In general the fact that the inheritance of traits is hard to quantify because parents usually provide both genes and environment was ignored. While the epigenetic process of X-chromosome inactivation was mentioned, Francis weirdly referred to this as a “leveling of the playing field” between genders without really explaining what this means. Also missing was any discussion of how conflicts of interest are played out through epigenetics (as illuminated by the work of David Haig).
By the time that this meandering interview was over, it was pretty clear that both host and guest were tired of the discussion.Development, Epigenetics, Gene by Environment Interactions, Genetics, Radio & Podcasts