Nature Versus Nurture: Which Is More Important?
Are your genetics more important? Or does the environment trump your genes? Researchers reveal the answer to the big “Nature versus Nurture” question … sort of.
Ellen Hendriksen, PhD
When it comes to mental health, the nature versus nurture debate continues to rage. As technology improves, fMRI images and genome sequencing demonstrate that mental illness is more biologically based than ever before believed. But the influence of life experience is indisputable. While the historical penchant for blaming mothers for a grown-up child’s mental illness (she was too cold, too smothering, too this, too that) has thankfully been largely squashed, there’s no denying that childhood experiences play a role in adult mental health.
But which is more important: nature or nurture?
Enter a 2015 study from the prestigious journal Nature Genetics, which undertook the lofty task of reanalyzing pretty much every twin study conducted over the past 50 years: 2,748 studies to be exact, which included over 29 million twins.
Why twin studies? Monozygotic (that is, identical) twins have the same genetic makeup, as they developed from the same fertilized egg. So, any differences between the twins are due, by extension, to the environment.
So, what’s the answer in the nature-nurture debate? According to the researchers, it’s about 50/50. Specifically, about 49 percent of variation among individuals is due to genetics, and 51 percent is due to the environment.
You might call this a nature-nurture draw, but at the same time, the study included heritability of traits from across the spectrum, from height (which is mostly genetic) to what the researchers dubbed “social values” (which are mostly environmental).
But what does the average of 50/50 tell us? In short, the conclusions we can draw are fewer than the questions the study prompts. In general, asking what percentage of a given trait is genetic or environmental is only one way to look at the nature-nurture balance, and perhaps not the most useful.
Another view is that genetics predisposes an individual to a disorder, like depression or OCD, and the environment tips the scales. In a less delicate analogy, genetics loads the gun, and the environment pulls the trigger.
Yet another way to look at the nature-nurture question is this: genetics determines a range of possible outcomes, and environment determines where on that range an individual lands; for example, in terms of IQ (which is a complicated concept in itself, but that’s another post), genetics determines the range of possible intellectual capacity, and the environment, from nutrition to years of education to number of books in the home, determines how far within that range an IQ will climb.
In sum, the 50-50 conclusion is more complicated than at first glance.
But look at it this way: either way, your parents are to blame.
Reference
Polderman, TJC, et al. (2015). Meta-analysis of the heritability of human traits based on fifty years of twin studies. Nature Genetics. doi:10.1038/ng.3285
Genetics image courtesy of Shutterstock.
About the Author
Dr. Ellen Hendriksen was the host of the Savvy Psychologist podcast from 2014 to 2019. She is a clinical psychologist at Boston University’s Center for Anxiety and Related Disorders (CARD). She earned her Ph.D. at UCLA and completed her training at Harvard Medical School. Her scientifically-based, zero-judgment approach is regularly featured in Psychology Today, Scientific American, The Huffington Post, and many other media outlets. Her debut book, HOW TO BE YOURSELF: Quiet Your Inner Critic and Rise Above Social Anxiety, was published in March 2018.