DNA and Heredity
You Inherited More Than You Think — And Less Than You Assume
The gene your grandmother carried might have skipped her entirely, skipped your parent, and then surfaced in you — having waited, silently, for decades.
The Idea
Most people walk away from a basic genetics education with a tidy mental model: two parents, two copies of every gene, one dominant, one recessive, traits flowing predictably down a family tree. It's a useful simplification. It's also a significant distortion of what actually happens. For a start, inheritance is profoundly non-linear. Each parent passes on roughly half their DNA to a child, but which half is determined by a shuffling process called recombination — chromosomes swap segments before being packaged into eggs or sperm. This means two siblings can share anywhere from about 37% to 62% of their DNA, despite having the same parents. The 50% figure is an average, not a guarantee. Then there's the question of what genes actually do — or rather, whether they're doing anything at all. Having a gene and expressing that gene are entirely different things. Gene expression is regulated by a vast, responsive machinery: proteins, chemical tags, non-coding RNA sequences, even signals from the environment. A gene can sit in your genome for a lifetime without ever being switched on. This is the domain of epigenetics — the study of how experience and environment leave marks on the genome that can, in some cases, even be passed on to children. What you inherited, then, is not a fixed blueprint. It's more like a score for an orchestra that still needs a conductor — and the conductor is context, chance, and circumstance.
In the World
In the aftermath of the Dutch Hunger Winter of 1944–45 — when a Nazi blockade reduced a population in the occupied Netherlands to starvation rations for nearly six months — researchers noticed something strange several decades later. The children born to women who had been pregnant during the famine showed elevated rates of obesity, diabetes, and cardiovascular disease. That was not entirely surprising; early malnutrition affects development. But then researchers looked at the grandchildren. The grandchildren — people who had never been hungry, whose parents had been born into relative postwar prosperity — still showed measurable differences in metabolic health compared to peers whose grandparents had not experienced the famine. Something had been passed on through the germline that wasn't in the DNA sequence itself. The prevailing hypothesis is that starvation had left epigenetic marks on the eggs and sperm of the famine survivors — chemical modifications that altered how certain genes were expressed, and that persisted into the next generation. This finding remains contested and actively studied. The mechanisms are not fully resolved. But the Dutch Hunger Winter cohort is one of the most striking pieces of evidence that heredity is not purely a matter of which DNA letters you received. The conditions your ancestors lived through — their hunger, their stress, perhaps even their joy — may have left faint but legible marks on the genome you carry today. What you inherited includes, in some sense, their history.
Why It Matters
This reframe quietly dismantles two opposing myths that people tend to carry about themselves. The first is genetic fatalism — the belief that having a particular variant means a particular fate, that your DNA is your destiny. The picture that actually emerges from modern genetics is far more dynamic: expression matters as much as sequence, and expression can change. The second myth is its inverse — the idea that genes are irrelevant, that everything comes down to choices and environment. That too turns out to be an oversimplification. The two forces are not in competition; they are continuously in dialogue. Practically, this should make you a little more humble about attributing any trait — in yourself or your children — to nature or nurture alone. It should also make family medical history feel more meaningful, not as a sentence, but as a map of tendencies worth knowing about. And it opens a genuinely interesting question about the self: if your genome is partly a record of your ancestors' environments, then in a real sense you are not only a product of your parents' DNA, but of their lives.
A Question to Ponder
If the experiences of your ancestors left faint traces in your biology, what traces might your own life — your habits, your stresses, your choices — be leaving for those who come after you?
Get a new one of these every morning.
Start learning with Thinkable