Epigenetics and Fitness

My column this week in the Globe and Mail looks at the links between epigenetics and fitness/health:

Skipped the gym yesterday? Oops – now your unborn kids, and their kids, are going to struggle with weight and cholesterol for their entire lives. If only you’d spent more time practising tennis, they’d inherit your devastating passing shot.

Or maybe not.

The nascent science of epigenetics, which enabled the research that won the 2012 Nobel Prize in medicine, is rewriting our understanding of how nature and nurture interact. Experiences in one generation can produce echoes in the next, contrary to what biologists believed for more than a century. But before you start feeling too guilty, it’s worth taking a closer look at what epigenetics does – and doesn’t – tell us about our future health and fitness, and how much of it you can actually control.

Your genes – about 24,000 of them – are encoded in the DNA you inherited from your parents and will pass on to your children. But DNA is only part of the story. A series of chemical markers determines which of those genes are switched on and which are suppressed, and these epigenetic markers (meaning “above the genes”) are affected by your lifestyle and environment.

[READ ON…]

Epigenetics is a fascinating topic that I’ve been wanting to write about for quite a while. When I actually sat down to do it, though, I discovered that the topic was quite a bit more complex and subtle than I’d realised. The ultra-simple understanding that’s been gaining currency over the last few years is that everything you do affects your epigenome, and some of those changes can be passed down to your descendents. That what I thought I’d be writing in theGlobe piece, but it turns out that epigenetic inheritance isn’t quite that straightforward. Still, it’s a pretty cool area of research.

If you’re interested in the topic and want to learn more, the first stop I’d recommend (after my Globe article, of course!) is this “deleted” book chapter from David Epstein’s bestseller The Sports Gene. Epstein ended up deciding that the research was too new and speculative to include in the book, so he pulled it before publication (and then agreed to publish it, with a cautionary disclaimer, on the sci-fi/futurist site io9). It’s a great intro to the field, and also provides appropriate context for how little we actually know at this point.

For a deeper dive, there was a special issue of the Journal of Physiology back in June devoted to the intersection of physiology with evolutionary biology, and how that’s changing our understanding of genetics and inheritance (thanks to Dr. Mike Joyner for pointing it out to me). Some points that caught my attention:

– What is a “gene”? The word dates back to 1909, and initially was an abstract term for the fundamental discrete unit of inheritance – i.e. if eye color is passed from parents to children, there must be a “gene” for eye color. As science advanced, the understanding of what a gene was evolved. First there was the realization that each gene was the “blueprint” for a specific protein with some function in the body; then, with the discovery of DNA, came the understanding of the gene as a transcribed code that contains the instructions for making the protein. But with advances in fields like epigenetics, the definition needs an update.

– The Modern Synthesis: In many ways, that view still dominates our understanding of human biology, in what’s often called the Modern Synthesis: we inherit DNA that contains the code for our genes; those genes contain the instructions for writing proteins that determine (at least in part) who we are. That view motivated the Human Genome Project, though the hoped-for one-to-one correspondence between specific genes and diseases didn’t materialize. Instead, most physical traits are influenced by a very large number of genes, each with relatively minor influence; and each gene may influence many different physical traits. (A factoid from the Journal of Physiology special issue: if you knock out a single gene in a yeast molecule, 80% of the time there’s no observable change.)

– What’s next? This is where epigenetics comes in – and in fact, epigenetics is just one of several mechanisms of “soft” inheritance that violate the dogma that acquired traits can’t be passed on to future generations. Direct epigenetic inheritance still seems to be quite rare, but there are some interesting possibilities to speculate about – for example, the fact that some types of epigenetic changes are “mutagenic,” raising the probability of a subsequent mutation in the actual DNA itself. That raises the intriguing possibility of “guided” evolution that doesn’t simply rely on random mutations sorted by natural selection.

Anyway, one thing I can safely conclude here is that I only have a superficial grasp of the meaning and importance of epigenetics. I’m looking forward to following the field and writing more about it in the future.