There is a *classic* debate in psychology about the importance of nature vs. nurture when raising children. Do children exhibit certain behaviors due to their biology and genetic makeup? Or, does the environment that a child grows up in dictate the bulk of their behaviors? If someone asked and you had to choose, would you say that people are shaped more by their inherited traits, or by their life experiences? Because of epigenetics, if someone asked me, I would say “both…but also kind of neither…”, keep reading to see if you’ll come to the same nature vs. nurture conundrum!
Epigenetics literally translates to "over" or "on top of" genetics. At its core, it is the way the environment and other factors can affect how genes are expressed and regulated. Understanding the importance of this is crucial! Because of epigenetics, we now know our genetic makeup is not solely based on our DNA that we have had since the sperm met the egg. From our development in utero, to the experiences we accumulate as we go through childhood, puberty, and beyond, the DNA that makes up our genes can undergo chemical changes that do not alter the specific DNA sequence. This makes “epigenetic changes” different than “genetic mutations” (as a brief aside, genetic mutations are what can lead to genetic disorders. Some common ones are Cystic Fibrosis, Down Syndrome, Tay-Sachs Disease, and even color blindness).
DNA methylation is an example of one of these epigenetic chemical changes in which a methyl group is added to the DNA structure, thereby altering its activity. Think of the methyl group like a tag that can be placed along the DNA structure. Usually, this tag makes the DNA code harder to read so it leads to genes being "turned off”, otherwise known as “decreasing gene expression”. These tags can be temporary or permanent depending on many variables like the specific gene to be coded as well as the length of exposure to a given environment. Okay, now that we have covered the nitty gritty, let’s get into some examples of epigenetics in action.
Going back to the 1990’s, and probably even before that, researchers documented that rat pups who were who were cared for appropriately (eg: ones that were groomed, licked, and nursed) by their mothers (we will call these “good mama rats”) went on to be calmer adults and had a lower stress response compared to rats that were not cared for as well. In the early 2000’s, researchers out of McGill University, Moshe Szyf and Michael Meaney, wanted to uncover why this was happening. They found that regardless of who the rat pup was born to, if they were raised by a “good mama rat”, they were much calmer and had a lower response to stress as an adult.
So, they went on to study the rats that were not raised by these “good mama rats”. In addition to having a heightened fight or flight response during a stressful encounter, these rats also had a methyl tag on a specific part of their DNA corresponding to a gene in the brain necessary for the moderation of the stress response. Even more interesting, this methyl tag was present on the DNA of these rat pups after only 6 days of being born. 6 days! This means that in the rat, what happens during the first 6 days of birth is enough to change the expression of certain stress-related genes and affect their behavior, even as an adult.
Performing studies like this in humans is inherently more complex. Scientists cannot have a well-controlled human study where they take babies away from their parents and place them in “good” households and “bad” households. That would be highly cruel and unethical, and not to mention, what makes a “good parent” for a human is not as black and white as in the rat – licking, grooming, and frequent nursing usually won’t cut it for infant humans! Even with these challenges, researchers have begun to look at the effect of low-socioeconomic status (SES) on DNA methylation and corresponding behavioral changes. The adverse outcomes (health, behavioral…etc) associated with social inequality has been observed for decades, but until recently, only educated guesses and hypotheses could be made to solve this apparent biological connection. A group of researchers from Northwestern University in 2019 studied 489 young adults from the Philippines and showed that low-SES and poverty are associated with changes in DNA methylation across 2,500 specific sites on 1,500 different genes. Since there are estimated to be about ~30,000 genes in the human genome (side note: this number is intensely debated!), this means that living in poverty may have an effect on ~5% of human genes. Additionally, many of the 1,500 genes identified are associated with biological systems and pathways that have been hypothesized to be associated with low-SES for decades, like immune function, skeletal development, and development of the nervous system. Now, instead of just an association, there is an apparent biological connection between the environment one is raised in and their future health outcomes and behavior.
With that in mind, what are your thoughts on nature vs. nurture? As always, get in touch with questions or comments below or through any of my social media!
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