There’s a 1 in 300 Chance That a Complete Stranger Is Your Cousin

26 June 2015
What can AncestryDNA help you discover?

New demographic research has revealed just how likely the British are to be closely related to a complete stranger they might meet in their homeland.

Analysis by AncestryDNA, part of the world’s largest online family history resource, of birth rates and population figures for the past two centuries suggests that the typical Brit has 193,000 living cousins. These relatives are sixth cousins or closer and share a common ancestor born in the last 200 years.

What this means – translating the facts:

  • If you walk across Britain, you’ll find about two cousins per square mile.
  • With over 61 million people in the UK, the average Brit will have enough cousins to fill Wembley Stadium twice.
  • If you finished first in the London Marathon, 111 of your relatives may follow you across the finish line.
  • A cruise on the world’s largest liner would give you the chance to meet nearly 20 relatives at the buffet.
  • Londoners share their daily tube commute with 12,000 unknown relations and will ride with a cousin on one in four (24%) bus journeys.


Researchers at the site mined birth rates and census data from the last two centuries to build a model that estimates how many close living relatives each of us has. The model suggests that the typical Brit has five first cousins, right up to 174,000 sixth cousins (see table one).


Type and number of living cousins for the average Brit


Type of relation


Approximate number of relatives of that relation alive today (3 s.f.)


1st cousin


2nd cousin


3rd cousin


4th cousin


5th cousin


6th cousin


Total number of 6th cousin or closer



The research follows the launch of AncestryDNA in the UK and Ireland. This new DNA matching service allows people to discover more about themselves and their family history and also connect with relatives they previously didn’t know existed.

The AncestryDNA test uses microarray-based autosomal DNA testing, which surveys a person’s entire genome at over 700,000 locations via a simple saliva sample. Analysis of the DNA data provides an estimate of the locations of ancestors from 26 separate world-wide populations, including Great Britain and Ireland, Europe, Scandinavia, Asia and South and North Africa.

In contrast to Y-chromosome or mitochondrial DNA tests, which only test one line of your family and generally provide information about ancestry several thousand years ago, the AncestryDNA autosomal test targets the last few hundred or thousand years. This enables people to learn more about their more immediate family history and uncover new family connections with other people who have taken the test.

Commenting on the research, Brad Argent, Commercial Director at Ancestry said: “It’s incredible to think that many of us will be in daily contact with unknown relatives – with no idea that we share much more than the same sporting team or commute to work.”

Which means Brits might want to think twice about how they treat that stranger standing next to them on the tube or in the shop. They might be family.