How your genes change what they do without changing what they are

Every cell in your body carries the same DNA, yet a liver cell and a neuron behave nothing alike. The same person's immune cells look different in a molecular readout after a month of illness than they did before it. Nothing in the DNA sequence changed in either case. What changed is which genes are being used — and that layer, sitting between the genome you inherited and the body you actually have, is where a great deal of biology happens.

The genome is a library, not a script

A useful way to picture it: your DNA is a library of instructions, and no cell reads all of them. Gene expression is the process of a gene being read and acted upon — transcribed into RNA, and usually then translated into a protein that does something. A gene that is never transcribed might as well not be there, for that cell, on that day.

Cells differ because they express different subsets. The full pattern of what is being transcribed at a given moment is called the transcriptome, and unlike the genome it is not fixed. It shifts with age, infection, stress, temperature, exercise, sleep and food. Reading the transcriptome is therefore closer to reading what a body is currently doing than to reading what it is made of.

Epigenetics: the marks that decide what gets read

Cells need a way to remember which genes should stay accessible and which should stay shut. That is what epigenetic marks do — chemical annotations sitting on top of the DNA without altering its letters.

The best-studied is DNA methylation: attaching a methyl group to a cytosine base, typically at sites where a C sits next to a G. Heavy methylation in a gene's control region usually keeps it quiet; loss of it tends to open the gene up. A second layer works through histones, the proteins DNA is wound around, whose chemical modifications control how tightly a stretch of DNA is packed and therefore how reachable it is.

The important property is that these marks are both stable enough to persist through cell division and responsive enough to change with circumstance. Diet, smoking, pollution, infection and chronic stress all leave measurable methylation changes. This is what people mean by "environment affecting your genes" — not that the sequence is edited, but that the annotations on it are rewritten.

Your genome is the hand you were dealt. Expression and methylation are how the hand gets played — and the same cards produce very different games depending on where you are sitting.

A test case: two communities, one ancestry, different lives

Separating the effect of lifestyle from the effect of genetics is hard, because populations that live differently are usually also related differently. A bioRxiv preprint posted on 9 August 2026 (10.64898/2026.08.09.743820) examines a situation where the two can be pulled apart.

The Punan of Borneo include the Punan Batu, who still practise mobile foraging, and the Punan Tubu, who were resettled and have farmed for roughly three generations. The two share deep common ancestry, and the authors report no detectable gene flow from agricultural neighbours since the groups diverged. That makes the difference between them mostly a difference in how they live rather than in what they inherited.

Profiling whole genomes, blood transcriptomes and DNA methylation across both groups and a neighbouring farming community, the Lundayeh, the authors report that the resettled Punan now resemble the farmers more closely than they resemble their own still-foraging relatives — 87% fewer differentially expressed genes in the Punan Tubu–Lundayeh comparison, and what they describe as a 77% shift toward an agricultural molecular state. Genes involved in fat metabolism and immune function account for much of it.

Three things must be said plainly about this. It is a preprint and has not been peer reviewed, so it has not yet passed the independent scrutiny described in our explainer on peer review. It covers three communities, not humanity — it is a well-designed case, not a general law about human populations. And it is not a verdict on which way of living is healthier. The paper reports convergence: one group's molecular profile moved toward another's. It does not say that movement was good or bad, and reading it as an argument for or against either diet would be reading something that is not there.

What it does support is the timescale point. Molecular profiles can shift substantially within about three generations — far faster than the genome itself evolves.

Why it matters for students and researchers

This layer is where genetics meets everything else: nutrition, public health, environmental science and medicine. It underpins epigenetic clocks that estimate biological age, the developmental-origins work linking early-life conditions to adult disease risk, pharmacoepigenetics, and cancer research where methylation changes are both cause and biomarker. It also demands care — epigenetics is heavily over-claimed in popular coverage, and the honest position is that environment demonstrably alters expression while the strength, permanence and heritability of specific effects are still being established. Following the peer-reviewed literature is how life-science and medical students and professionals tell a robust finding from an appealing one.

Frequently asked questions

What is gene expression?

Gene expression is the process by which the information in a gene is read and used — transcribed into RNA and usually translated into a protein. Which genes a cell expresses determines what that cell does, which is why cells with identical DNA can behave completely differently.

What is DNA methylation?

DNA methylation is the attachment of a methyl group to a DNA base, usually a cytosine followed by a guanine. It acts as a chemical annotation that generally silences a gene when present in its control region, and it can change in response to diet, environment and age without altering the DNA sequence.

Can lifestyle really change how your genes work?

Yes, in the sense that diet, activity, pollution, infection and stress measurably alter gene expression and methylation patterns. The DNA sequence itself is not rewritten. How large, lasting and inheritable specific changes are remains an active research question rather than a settled one.

What did the 2026 Borneo preprint find?

It reports that a Punan community resettled into farming about three generations ago now resembles neighbouring farmers more than its own still-foraging relatives in gene expression and methylation, despite shared ancestry and no detected gene flow. It is a preprint that has not been peer reviewed, covers three communities, and does not claim either lifestyle is healthier.