March 2025 newsletter: I’m as happy as the next person to blame my parents for my assorted (minor) character flaws. And after doing genetic testing, I also get to conveniently blame ancestors I never met for things like my tendency to thrash about at night—at least until I got a memory foam mattress, at which point I stopped moving at all.
Yes, the classic nature (genetics) versus nurture (environment) debate.
Except, it turns out that neither nature nor nurture are quite what we thought. As our understanding of both has grown, we’ve realized that randomness plays a huge role in shaping who we are as adults. And when we look closely, even the supposed boundary between nature and nurture starts to break down.
“Simplicity can be good for communicating scientific information, but oversimplification can be damaging. Biology is far too complicated to be boiled down to two percentages attributing cause to genes versus environment. Even more importantly, the real problem with the concept of heritability is that it assumes that our genes and our environment don’t work together. That’s the major flawed assumption—that they can be divided as causes.’ Robert O Wright, Nature versus nurture—on the origins of a specious argument. Exposome, Volume 2, Issue 1, 2022.
Way back, waaayyyy back, I earned a BSc in genetics. Sequencing the human genome was still nearly thirty years away. My strongest memory of those studies is of a laboratory aflutter with ether-intoxicated fruit flies whose parents I may or may not have irradiated, my fuzzy recollections possibly due to the aforementioned ether. Or the radiation exposure.
But, even though I’ve never worked in the field of genetics, I still get a frisson of excitement over advances and new understandings in the field, such as full-genome sequencing, mitochondrial eve, CRISPR gene editing, and epigenetics.
Back in the day, the received wisdom was that vast areas of chromosomes (98%, in fact) were comprised of so-called “junk DNA.” That label always irked me, as if someone with clout had simply shrugged and declared, “I have no clue what it does, so it must be useless.” And so it was decreed.
I promise this isn’t a complete tangent; it all comes back to nature vs. nurture. It turns out that much of this so-called junk DNA is actually part of the epigenome, which acts as a behind-the-scenes boss. And the epigenome is the behind-the-scenes boss that tells your ‘coding’ genes when to turn on, when to shut up, and how much influence they should have. And epigenetics doesn’t just regulate gene expression—it responds dynamically to environmental factors, meaning what happens to us influences how our genes behave.
And, just to keep things interesting, it’s also inheritable. Stress. Nutrition. Your mother being scared by a ghost while pregnant with you. All things we’d usually chalk up to the nurture side of the equation.
Then add in the wildcard: chance. Genetic mutations, random molecular hiccups, and stochastic (inherently unpredictable) events during development, especially fetal development, introduce a whole layer of unpredictability. These elements of chance significantly shape who we become, often in ways we don’t yet fully understand.
Which brings us back to blaming our parents. The thing we usually think of as nurture—our actual upbringing—apparently has a much smaller influence than expected.
In the 2022 article in New Scientist, Nature, nurture, luck: Why you are more than just genes and upbringing, Clare Wilson explains: “…DNA often accounts for about half of the difference between individuals. The effects of upbringing, on the other hand, are much smaller, ranging from 17 percent to as little as 0 percent… we should really see ourselves as the product of nature, nurture and ‘noise.'”
She quotes Eric Turkheimer at the University of Virginia: “In adoption studies, correlations between characteristics of families and adopted children are basically zero…” And adds: “A notable exception is intelligence, where the impact of upbringing is around 25 per cent during childhood. However, this dwindles to almost nothing in adulthood, when any effects from hothouse schooling or pushy parenting fade and people have much more control over their intellectual lives. There is also a caveat – in cases of childhood abuse, the environmental impacts can have large and lasting effects.”
So, if nature and nurture are tangled together and randomness plays the deciding role, maybe we should rethink how much credit (or blame) we assign to our genes and upbringing. Perhaps we’re all just creatures of chance, navigating a life path shaped by a mix of DNA, environmental factors, and the unpredictable roll of the cosmic dice.
You might also want to have a look at these. Both are freely available.
- The Complex Truth About ‘Junk DNA’ by Jake Buehler. Quanta Magazine, 2021
- How Epigenetics Influences Animal Behavior and Evolution, by Maria Faith Saligumba. Wild Science. Feb 2025