For £200 you can get a DNA test that claims to tell you who your ancient ancestors were. But do these tests really work? Sense About Science explains why scientists are warning that these tests often aren’t worth it.
Commercial ‘genetic ancestry tests’ offer people a profile of their genetic history based on a DNA sample: you send off a sample of your saliva and the test findings may come back to tell you that you are descended from groups such as Aboriginals or Vikings, or related to famous figures such as Napoleon or Cleopatra.
Sounds great, but at Sense About Science, we don’t think these tests are what they claim to be.
Are commercial DNA tests accurate?
The tests are part of a rapidly growing market for genealogy, and ancestry is now big business. Thousands of people are taking DNA ancestry tests every year, with at least 40 companies offering tests internationally. They don’t provide accurate information about an individual’s ancestry, so people aren’t getting what they are paying for.
There are legitimate ways to look at personal genetic history (genetic genealogy), but these are based on much more than an individual’s DNA tests in isolation. They are based on databases of genetic information about many other people, historical records, information about surnames, and so on.
This is why Sense About Science has been working with genetics researchers to explain why commercial DNA tests cannot provide accurate stories about personal ancestry. This month we launched a briefing, Sense About Genetic Ancestry Testing, which comes with a warning: don’t be fooled by the appeal of an exotic lineage or a notorious ancestor.
Many of the claims about such histories are either so general as to be personally meaningless, or they are just speculation from thin evidence.
Finding out your individual ancestry
Our individual ancestry is much shallower than people might imagine. The best current estimate from genetics research is that the most recent person everyone alive today is descended from lived just 3,500 years ago.
And patterns of ancestry are complicated. As you look back through time you quickly accumulate more ancestors than you have sections of DNA. This means you have ancestors from whom you have inherited no DNA.
The genetic ancestry business uses a widespread phenomenon where general information is interpreted as being more personal than it really is (the ‘Forer effect’), similar to how horoscopes work.
The reality is that there are millions of possible ‘stories’ of your ancestry. To find out whether any one of them is likely to be true, you would need to use statistics to test its likelihood compared to other possibilities. Your DNA cannot be read like a book or the map of a journey. Ancestry is more complicated.
So are you descended from Vikings? You may well be… but so are many of us. Think before you part with your money: everyone’s interested in where they come from, but you might be better off to start by searching through your loft or chatting to your Grandma.
Which? Conversation provides guest spots to external contributors. This is from Tabitha Innocent, Scientific Liaison at Sense About Science. All opinions expressed here are Tabitha’s own, not necessarily those of Which?