杏吧原创

A MURDER has been committed, and all the cops have to go on is a trace of DNA left at the scene. It doesn鈥檛 match any profile in databases of known criminals, and the trail goes cold. But what if the police could issue a wanted poster based on a realistic 鈥減hotofit鈥� likeness built from that DNA?

Not if, but when, claim researchers who have developed a method for determining how our genes influence facial shape. One day, the technique may even allow us to gaze into the faces of extinct human-like species that interbred with our own ancestors.

It鈥檚 already possible to make some inferences about the appearance of crime suspects from their DNA alone, including their racial ancestry and some shades of hair colour. And in 2012, a team led by of Erasmus University Medical Center in Rotterdam, the Netherlands, identified five genetic variants with detectable effects on facial shape. It was a start, but still a long way from reliable genetic photofits.

To take the idea a step further, a team led by population geneticist of Pennsylvania State University and imaging specialist of the Catholic University of Leuven (KUL) in Belgium used a stereoscopic camera to capture 3D images of almost 600 volunteers from populations with mixed European and West African ancestry. Because people from Europe and Africa tend to have differently shaped faces, studying people with mixed ancestry affecting facial structure.

Kayser鈥檚 study had looked for genes that affected the relative positions of nine facial 鈥渓andmarks鈥�, including the middle of each eyeball and the tip of the nose. By contrast, Claes and Shriver superimposed a mesh of more than 7000 points onto the scanned 3D images and recorded the precise location of each point. They also developed a statistical model to consider how genes, sex and racial ancestry affect the position of these points and therefore the overall shape of the face.

Next the researchers tested each of the volunteers for 76 genetic variants in genes that were already known to cause facial abnormalities when mutated. They reasoned that normal variation in genes that can cause such problems might have a subtle effect on the shape of the face. After using their model to control for the effects of sex and ancestry, they found 24 variants in 20 different genes that seemed to be useful predictors of facial shape ().

Reconstructions based on these variants alone aren鈥檛 yet ready for routine use by crime labs, the researchers admit. Still, Shriver is already working with police to see if the method can help find the perpetrator in two cases of serial rape in Pennsylvania, for which police are desperate for new clues.

To get a sense of the method鈥檚 current power, New 杏吧原创 asked Claes and Shriver to predict the appearance of a young woman based on a scan of her DNA performed by the Californian company . You can judge for yourself how closely their prediction resembles former New 杏吧原创 reporter Sara Reardon in the photos below.

Narrow the search

The next step is to run larger studies in different populations to confirm that the variants found so far are statistically reliable. The researchers also plan to use the method to discover further genetic variants that affect facial structure. 鈥淚 believe that in five to 10 years鈥� time, we will be able to computationally predict a face,鈥� says Claes.

鈥淚n five to 10 years鈥� time we will be able to predict a person鈥檚 face from their DNA profile鈥�

Even if it becomes possible to produce accurately reconstructed faces, the photofits wouldn鈥檛 be used as evidence in a criminal trial. Instead, any person identified via the images would have their DNA compared to the crime scene sample in the usual way. In that sense, the technique is more like psychological profiling, used to narrow the search for a suspect, than conventional forensic DNA testing.

of the University of North Texas in Fort Worth, formerly the FBI鈥檚 leading expert on forensic DNA analysis, hopes that the method will also lead to better facial reconstructions of people from skeletal remains. 鈥淚t鈥檚 an easier step, because the skull gives you an anchor,鈥� Budowle says. 鈥淚f you have genetic information that could guide the artist, so that they鈥檙e not just freewheeling it, that might help us identify the remains.鈥�

Then there is the intriguing possibility of producing facial reconstructions of extinct human relatives. Even for Neanderthals, where there are numerous fossil skulls, palaeoanthropologists have little idea about the soft tissues of the face. 鈥淲e don鈥檛 know how far out their noses extended,鈥� says Shriver. This means that artists鈥� impressions of what the species looked like are partly guesswork. Shriver hopes that there will be enough overlap between the Neanderthal and modern human genomes for variants that influence face shape to start filling in such gaps.

鈥淭he technique could also allow us to create facial reconstructions of extinct human relatives鈥�

For other ancient hominins, such as the Denisovans 鈥� who once occupied a vast expanse of Asia from Siberia to Indonesia 鈥� there are so far no confirmed skulls to go from, so reconstruction from DNA is the best hope of putting a face to the species name.

Both the Neanderthals and Denisovans interbred on occasion with our own ancestors, leaving telltale traces of their DNA in some modern human genomes. Indeed, evolutionary geneticists believe that early Homo sapiens hybridised with a variety of extinct hominins, which means that the human genome should be littered with signatures of these ancient cross-species sexual encounters.

of the University of Washington in Seattle, who is looking for such DNA 鈥渇ossils鈥�, is excited about the possibility of using these to reconstruct what the extinct hominins may have looked like. 鈥淲e鈥檙e not quite there yet,鈥� he says. 鈥淏ut this ultimately might be a really profound tool.鈥�

Leader: 鈥�Facing up to the limits of DNA-based forensics鈥�

This article appeared in print under the headline 鈥淒NA mugshot gives cops another lead鈥�