An article by Stephen Johnson in the BigThink web site states:
“The theory of evolution holds that all living things have common ancestors. But just how far back do humans need to go to find a common ancestor of their own: a person to whom all living people are related?
“The answer, for people of European descent at least, is surprisingly recent: 600 years. The common ancestor for every single person alive on the planet today, no matter where, lived approximately 3,600 years ago. That means Confucius, Nefertiti, Socrates, and any figure from ancient history that had children, is in some way your ancestor.”
The article then goes on to describe the findings in a new book by Adam Rutherford titled A Brief History of Everyone Who Ever Lived, which explores efforts within mathematics and science to describe human ancestry on a grand scale.
I also wrote about this more than two years ago in an article entitled We Are All Related! So Get Over It. As I wrote at the time, “Of course, most every person in North America whose ancestors have been here for several generations is related to most everyone else in North America whose ancestors have been here for several generations. In fact, you and I are probably related, and we are also probably related to Barack Obama, Donald Trump, Justin Bieber, Celine Dion, and the local mailman.”
The article is still available at: https://blog.eogn.com/2015/08/25/we-are-all-related-so-get-over-it/.