Picture the scene. A detective is addressing her team:



“The DNA test results are in. We’re looking for a white male suspect, 34–37 years old, born in the summer in a temperate climate. He’s used cocaine in the past. His mother smoked, but he doesn’t. He drinks heavily, like his Dad. We’re seeing high stress levels, and looking at the air pollution markers, let’s start looking downtown, probably near a major intersection”.

Science fiction? Yes, for now. But advances in epigenetics – the study of reversible chemical modifications to chromosomes that play a role in determining which genes are activated in which cells – might soon start making their way out of research labs and into criminal forensics facilities.

Take the idea of the epigenetic clock, one of the ways in which our cells and DNA can betray our age. Epigenetic patterns change throughout our lives, along broadly predictable paths, making it possible to infer age from DNA samples.

Steve Horvath at UCLA has developed a statistical model based on 350 potential epigenetic modification positions in the human genome that can estimate your age to within three and a half years. The rate of epigenetic aging seems to depend somewhat on race, and can be affected by some health conditions, but this kind of test is already at the stage when forensics labs are validating it for use in criminal investigations.

The things we get up to while our epigenetic clocks are ticking can also leave their mark on our DNA. Cigarette smoking correlates with characteristic and persistent epigenetic changes. The same goes for cocaine, opioids and other illicit substances. There’s also some evidence for epigenetic signatures of obesity, traumatic childhood experiences, exposure to tobacco in the womb, season of birth, exposure to environmental pollution, exercise, and possibly even the things our parents and grandparents did before we were born.

There are also ways to detect non-epigenetic evidence of environmental exposures that we all experience For example, international travel or exposure to certain chemicals or experiences can change the composition of the microbiome (the collection of bacteria, viruses and fungi found in and on our bodies). Tests based on these observations might also eventually find their way into forensic science.

Unless there’s an urgent need to tell the difference between a pair of identical twins – for example if one is suspected of murder – none of these tests are likely to appear in court in the immediate future. There needs to be extensive validation before we know if these findings are specific and sensitive enough to be useful. Existing epigenetic analysis methods also use impracticably large samples of blood or tissue, much more than is usually available at a crime scene.

However, these technical challenges will hopefully soon be overcome, and it’s not too early to start thinking about the legal implications of this type of information. Do we want law enforcement agencies and governments to know the details of our personal and family histories, our vices and habits? Can epigenetic evidence be presented accurately by lawyers, and interpreted appropriately by jurors? Even intelligent people without statistical training can struggle with the concepts of, for example, probabilities in the context of DNA fingerprinting.

And if as a juror you’re supposed to decide somebody’s guilt or innocence based on evidence of the crime, what bias might be introduced by knowing their epigenetic history – or that of the victim?

There are no easy answers, and there is the potential to do great harm if these shiny new technologies are applied inappropriately. Epigenetics is an exciting and fast-moving science; let’s hope that the legal and ethical fields can keep up with it.

Cath Ennis’ book “Introducing Epigenetics: A Graphic Guide” (with Oliver Pugh) is out now in the UK, and can be pre-ordered for March release elsewhere