The Malaysian Insider

By Andy Ho

OCT 31 — It was reported last week that genealogical records show that movie stars Matt Damon (picture) and Ben Affleck, childhood buddies in Boston and now collaborators in Hollywood, are also 10th cousins, once removed. Their most recent common ancestor was an Englishman called William Knowlton Jr who had arrived in Massachusetts in the 1630s.

Affleck is also related to the late Princess Diana and 16 US presidents — including Barack Obama, who is also a 10th cousin, once removed, from George W. Bush. Obama is also related to Gerald Ford, Lyndon Johnson, Harry S. Truman, Winston Churchill — and actor Brad Pitt.

Likewise, the records indicate that Hillary Clinton is related to singers Madonna and Celine Dion, as well as Prince Charles' wife Camilla Parker-Bowles — and actress Angelina Jolie.

The most recent common ancestor whom the current and immediate past presidents of the United States share is Samuel Hinkley, who died in 1662 in Cape Cod, Massachusetts. Clinton and Jolie are connected by their most recent common ancestor, Jean Cusson, who died in St Sulpice in Quebec, Canada, in 1718.

For these famous folk, one does not seem to have to go back more than about three centuries to hit a common ancestor. Are such tantalising links unique to leaders, suggesting perhaps that leaders are born, not made? Is this short length of time also unique to born leaders?

Probably not.

About 10 years ago, a Yale professor of statistics showed that all human beings — not just leaders — are mathematically descended from common ancestors in the not-so-distant past. In a 1999 study published in Advances In Applied Probability, Professor Joseph Chang showed that only 32 generations of 30 years each — about a millennium — were needed going back genealogically to hit the one common ancestor that everyone alive in the world shares.

However, his model assumed that people mated randomly in a universal free market without regard to geography, culture or migration. Still, the insight was that we all come from a common ancestor pool that existed just a few millennia, and not hundreds of thousands of years, ago.

The Massachusetts Institute of Technology's Douglas Rohde then wrote a massive computer simulation program which factored in how human mating is socially impelled and the fact that people have always migrated. The simulation was a re-run of the genealogical history of humankind.

In 2004, Chang, Rohde and another co-worker published a paper in Nature about the simulation, which showed how the most recent ancestor common to everyone alive today lived only 2,000 to 5,000 years ago. Allowing for very minimal migration gave the 5,000-year figure. Conversely, higher migration rates gave a figure on the lower end of the range.

Going back even further, past 5,000 to 7,000 years ago, we come to a period in time when every individual alive then was an ancestor to everyone living today — unless they had no babies at all. All individuals alive at that time would comprise the top layer of the family trees of all six billion people alive today (unless they died without issue).

That is, everyone alive today is descended genealogically from the same ancestral population set that lived five to seven millennia ago. Thus, if you had a time machine to fly you back to 3,000-5,000BC, anyone you met at random — whatever your ethnicity — would likely be your genealogical ancestor (unless he or she died without issue).

Incredible? Not really.

Everyone has two parents, four grandparents, eight great-grandparents, 16 great-great-grandparents, and so on. As it doubles in this manner, one soon has thousands of ancestors within centuries.

However, the further back in time, the smaller the earth's population. Thus, each individual in the past begins to appear in the family trees of more and more of the people who are alive today.

If we went back along our family trees far enough, we will come to a point when there was one person who appears at least once on everyone's family tree. Going back even further than that, the earth's population gets even smaller, so we will arrive at a point when everyone alive at that time must be an ancestor to all who are alive today — unless he or she died without issue.

To reiterate, the most recent ancestor common to everyone alive in the world today lived within the last few thousand years. And a few thousand years before that was to be found the same set of ancestors for everyone on earth today.

The amazing insight is that one has to go back only a few millennia to find the common pool of ancestors for everyone alive today.

Notice that you need just one ancestor of yours to migrate and marry outside your group to link you up to millions of ancestors that everyone in that outgroup had.

However, to be genealogically related to, say, the first emperor of a united China, Qin Shih Huang (259-210BC), is not the same as receiving DNA from him. Because chromosomes re-arrange themselves structurally as a necessary part of normal differentiation and development in the embryo in every generation, the amount of DNA that I may have got from him might be near to zero.

So while it is very likely for us to trace our genealogy to some historical figure, the same cannot be said genomically. All of us probably have nobility among our ancestry. But genomic mixing along the genealogical branches means that after just tens of generations, there will be little or no blue blood left in us.

In short, genealogy and genes can be as different as chalk and cheese. — Straits Times