Video Review: The DNA Journey

'There are three kinds of lies,' Mark Twain once said Benjamin Disraeli once said. 'Lies, damned lies, and viral advertising campaigns.' It's possible I made up part of that quote but with all the recent talk of a post-fact Britain, it probably doesn't matter. Science says we're all going to believe what we already want to believe anyway.

That's the cynical inner journey I went on while watching The DNA Journey, part of an advertising campaign produced for travel comparison site momondo. The five-minute film shows – through the magic of genetic ancestry testing – how we're all related through a shared and deep history.

It's a slickly crafted narrative, hitting all the major plot points. In act one, the viewer is treated to a series of vignettes from a cast of borderline xenophobes talking about how their countries are better than everyone else's. Jay, a proud English lad, is 'not a fan of the Germans'. Aurelie says of her French compatriots, 'We're just the best, you know, it's just fact.' But Carlos from Cuba doesn't like the French. 'I'm more important than you,' declares an unnamed blond Icelander. 'I am strong'. It's like The Apprentice for bigots. Like The Apprentice.

With everyone's nationalist cards laid on the table, a man in scientific-looking round spectacles explains how you inherit half your genes from each parent, who inherit half from each of theirs and so on, before proffering a vial to the contestants – the gateway to their DNA journeys.

'What could you possibly tell me that I don't know?' Jay the Tottenham lad sneers, snorting and hocking a glob of phlegm into the tube, becoming an emblem for everything in the world that simultaneously annoys and scares me.

Two weeks later (we're told), the contestants shuffle back into the room and sit together expectantly; an awkward melange of jingoist stereotypes. Exactly at the midpoint, we get the first histrionic reactions to their DNA tests. Aurelie more or less breaks down; Carlos is quite endearingly wide-eyed with surprise; and Ellaha, a Kurdish woman who isn't so fond of Turkey, shakes with anticipation.

Now the moment of what I'll charitably call 'truth'. Upon opening their envelopes, the contestants discover how they are not what they thought themselves to be. Aurelie, for example, is nearly one-third British while Jay discovers, grudgingly, that he's five percent German.

So far so climatic, but there's more. The DNA expert witters poetically about how we are all, in a sense, cousins before the shock (!) twist that Ellaha actually has a cousin in the room. Everyone cheers, there's more crying and emotional thanks.

Remarkable how a little spit can prise open even the most closed mind. It's all very noble and the earnestness of everyone involved swells my tiny heart. But it's a bit of a sham.

The DNA expert isn't a DNA expert: he's Brad Argent, a spokesperson for AncestryDNA, the company that provided the genetic testing. The other interviewer is an actor who once played Mrs Potts in a stage production of Beauty and the Beast. Some of the contestants are actors too, which explains why they're suspiciously attractive.

Does it matter? Momondo explained that everyone's DNA tests and reactions were their own; nothing was scripted. The story of Ellaha's newfound cousin is true, although it turns out they're 'distant' cousins, which is a bit less exciting (not to mention a whole lot less informative). But does it matter as long as they did a good job with the science?

The testing company they used, AncestryDNA, analyses your autosomal DNA – the strings of chemicals inside each of your trillions of cells (not including the sex chromosomes). By comparing your strings of genetic information with those belonging to other people in the company's database, you can find distant relatives who would be hard to trace using only the more conventional genealogical methods of historical records and other paper trails.

The main emotional thrust of the advert related to ethnicity – what percentage of your DNA is Turkish, perhaps, or German? These 'ethnicity estimates', also called 'biogeographical ancestry' or 'admixture' reports, work by comparing your DNA to a reference database of genetic markers labelled as coming from certain places. Genealogist and writer Debbie Kennett described this sort of test to BioNews as 'not much more than a party piece'.

'They are focused on recent shared ancestry,' Kennett told me, 'and can only reliably distinguish populations at the broad continental level (i.e. Europe, Asia and Africa).'

Within a continent, on the other hand, there are no obvious boundaries where we can say Spanish DNA cleaves from French. Jay's German five percent likely came about because part of his genome matched a cluster of DNA labelled 'German' in the testing company's database. This doesn't necessarily mean Jay's family tree has any branches in Germany – it's just hard to figure out by genes alone. Using a different company, you might even end up with different percentages of ethnicity.

'You should treat the percentages beyond the continental level with a very large pinch of salt, and just regard the results as a bit of fun,' Kennett said.

So, while momondo's advert rightly shows that ancestry is messier than many give credit, it promotes a false kind of certainty out of an incomplete picture. But if that gets people out of their comfort zones and interested in the experiences of others, perhaps blurring some boundaries along the way, it's hard to hate.