DNA on the Shroud of Turin reveals plant, animal and human contaminants

Maybe the Shroud of Turin fascinates me so much because I was an editor at Nature when the journal published the supposedly definitive radiocarbon dating study in 1989 by teams in Oxford, Zurich and Arizona, which claimed ‘conclusive evidence’ that the linen from which this venerated relic is made is of medieval origin, dated to between 1260 and 1390.¹

It was around that time too that Nature received a fascinating paper proposing that the faint image on the Shroud – alleged by some to be that of Christ somehow imprinted when the cloth was used to wrap his body after the Crucifixion – was produced photographically.² (It’s violating no secrets to say that the paper was rejected after review, because its author Nicholas Allen has spoken publicly about his chagrin with that outcome.)

Dan Brown-style conspiracies abound: writers Christopher Knight and Robert Lomas have argued that the image is in fact that of Jean de Molay, leader of the Knights Templar when the military order was violently disbanded by the French King Phillipe Le Bel in 1312.³ Come on: what’s not to love here?

But the fact remains that the Shroud is a tantalising object of scientific study. The ‘conclusive’ radiocarbon dating has been called into question because of apparent discrepancies among the data sets of the three labs.⁴ And Italian attorney and author Mark Antonacci has argued that a wider body of evidence supports a more complex history than a simple medieval forgery.⁵ Specifically: the Shroud might indeed have originated in the Holy Land around the time of Christ, been kept in the region of modern-day Turkey for centuries, and finally transferred to Constantinople for the Byzantine emperors until brought to Western Europe after the sacking of that city in the scandalous Fourth Crusade of 1204. It first surfaces definitively in the household of a French noble with Templar connections in the 1350s, before finding its way to Turin in the 16th century.

New findings from old residues 

One reason these questions are so hard to resolve is that the current guardians of the Shroud in the Catholic church are reluctant to make it available for scientific analysis, whether because (as adherents might say) it is so precious or because (sceptics will charge) they don’t want its sacred status undermined by science. Even so, the literal scraps of the material accessible to analysis are still yielding new findings. The latest of these is a study of the DNA residues in threads taken from the cloth in 1978, some of which were used in the 1989 radiocarbon dating.⁶

This isn’t the first such DNA analysis. In 2015 a team in Italy reported results from dust particles vacuumed from parts of the cloth, which showed the genomic signatures of a variety of plants from the Mediterranean, the Middle East, Asia and the Americas.⁷ They also found human DNA from several people of diverse ethnic origins in Western Europe, the Arabian peninsula and the Indian subcontinent. All of this might be expected given the Shroud’s history since the Middle Ages, but the researchers pointed out that it is also consistent with the idea that the cloth arrived in Europe from the Middle East, and that perhaps the fabric itself was woven in India.

One is almost tempted to imagine the Shroud being used as a tablecloth

The new study, by a team including some of those involved in the 2015 work, uses a different method to analyse the DNA, not reliant on amplification by the polymerase chain reaction. Its findings are similar in many respects, but somewhat more specific: the plant DNA includes peanuts, tomatoes, bananas, oranges and carrots, and there are genomic traces of cattle, pigs, chickens and dogs. One is almost tempted to imagine the Shroud being used as a tablecloth for a late Renaissance banquet.

As for humans, there’s a clear genomic trace (from mitochondrial DNA, which reveals ethnic lineage) of the researcher who collected the threads in 1978, the Italian medical doctor Pierluigi Baima Bollone, who is a coauthor of the paper but died last November. The work also reveals the presence of DNA from Indian ethnic lineages as well as a rare lineage found today in an Arabic-speaking minority in the Holy Land: Jordan, Lebanon, Syria.

What should we make of all this? The paper’s authors are rightly circumspect. Could the cloth have simply been imported into 14th-century France from India, via the Mediterranean? Or do the Near and Middle Eastern signatures fit the tale of a longer history that brought it west via Constantinople? The case, as they say, continues.