EPIGENETICS: THE SCIENCE OF GENETIC MEMORY

Isobel Whitcomb ‘17

Environmental Columnist

When schools teach kids about evolution, they often begin with a story about two men: Jean-Baptiste Lamarck and Charles Darwin. In case you’ve blocked middle and high school out of your memory, here’s a quick refresher. Lamarck and Darwin were both naturalists who studied how species evolve. However, unlike his contemporary, Darwin, Lamarck did not believe in natural selection or extinction. Instead, Lamarck thought that species acquired characteristics and then passed them onto their offspring. If you think back hard enough, you might recall the ubiquitous giraffe example, in which the short-necked parent giraffe stretches its neck out to reach the tallest leaves, and subsequently, gives birth to a baby giraffe with a slightly longer neck who then stretches its neck out (and so on).

The main point of these lessons was that Lamarck is wrong, and Darwin is right. However, modern biology is finding that inheritance might not be so simple.

Enter epigenetic inheritance.

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Epigenetics is the process by which the expression of genes are affected by our environment. While genetic code is important in determining how organisms look, behave and function, the environment is also crucial in determining characteristics. For example, while identical twins have the same DNA, rarely do you meet a pair of adult identical twins who look exactly alike, at least if you look closely.

What causes two people with the exact same genetic code to look and act differently?

Much of epigenetics is a process that affects our genes on a minute, molecular level but doesn’t actually change the backbone of our genes - our DNA - in any way. Think of genetics this way: there’s your DNA, but there are also a whole lot of other processes happening around it. For example, in the most commonly studied mode of epigenetics, chemicals called methyl groups bind onto certain portions of a cell’s DNA. These methyl groups have the power to switch the traits encoded in the DNA on or off.

If only there was a way to pass on these epigenetic changes to offspring, things would begin to sound awfully Lamarckian. As it turns out, the most recent studies in epigenetic research show that epigenetic inheritance is a real occurrence, and it happens all the time.

For instance, one area of study that has garnered a lot of attention recently in both biology and psychology is the epigenetic inheritance of trauma. Some research in this area is showing that people who experience trauma pass on the effects of trauma to their children. However, other scientists are finding that parents who experience trauma pass on increased resilience. Rachel Yehuda, at James J. Peters Veterans Affairs Medical Center found in her study of the survivors of the Nazi Holocaust and their children, that holocaust survivors had 10% higher methylation, which promotes the expression of a gene associated with PTSD and depression. However, their children had 7.7% lower methylation at that site, indicating an increased resilience to stress.

While epigenetics complicates the way we look at evolution, it’s important to note that these changes don’t indicate that Lamarck was correct in any way. The fact is that Lamarck had no idea genes existed, so he could not have predicted the complexity of the interaction between inheritance and environment. Epigenetics is not an alternative to the Darwinian view of evolution. Instead, it provides us with a more nuanced and detailed view of the way genetics and evolution works.