Charlemagne, Mohammed, Confucius — major figures in history and also your relatives, according to Joseph Chang.

Chang, director of undergraduate studies of statistics and applied mathematics, uses statistics in an evolutionary context to explore ancestral relationships spanning thousands of years. According to “Modeling the Recent Common Ancestry of All Living Humans,” an article published by Chang in September’s Nature, man’s most recent common ancestor lived as recently as 1200 A.D.

The paper was an update of his previous publication on the same subject, a first attempt which used an intentionally simplified model that ignored geography and migration, he said.

“It’s difficult to analyze a realistic model mathematically, so the previous model started with the assumption of a homogenous world, of random mating,” Chang said. “This time, we added the essence of geography by assuming very little communication between continents or islands in the world.”

Chang collaborated on the paper with Douglas Rhode of the Massachusetts Institute of Technology and Steve Olson, who was supported by the National Institutes of Health.

The concept of a most recent common ancestor is based the laws of probability with large numbers. The farther back in history one looks, the greater the likelihood of finding someone who was a common ancestor to any two people today. Following this logic, one need only go back far enough to find a direct ancestor of all humans currently alive.

“It’s kind of like winning the lottery in a way,” Chang said. “This person isn’t special, if you go back further everyone wins that lottery.”

Chang said the paper incorporates geography by subdividing land as units and using probability theory to determine the likelihood of certain combinations of parents and offspring. It also utilizes computational models to simulate socially driven mating, physical barriers of geography and migration, and recorded historical events.

Chang admitted that the study is still somewhat speculative due to the ambiguity of human migration and interaction patterns, but he noted that the computer program is easy to change to incorporate different assumptions.

Previous studies focused on models which depended on mitochondrial DNA, which an individual inherits from his or her mother. Scientists measured the predictable interval of DNA mutations over thousands of years to calculate how many generations ago two individuals had a common ancestor.

“They’re answering different questions,” Chang said. “This only takes into account the mother’s mother’s mother, whereas we address ‘ancestor’ the way we mean it in the spoken context.”

Chang said his paper also introduced the “identical ancestors point,” a date at which all individuals were either ancestors of everyone alive today, or ancestors of no one alive today.

Andrew Hill, chair of the Anthropology department, said the significance of finding the MRCA is still questionable, as it is just the logical and inevitable convergence of certain genes.

“Genetically, that person is not the origin of species; it’s the origin mostly of certain molecular strands,” Hill says. “When you look at the whole of human evolution, what this paper is talking about is the top little bit.”

But Chang said the finding is relevant partly due to the familial implications.

“It says something about how closely related we all are,” Chang said. “Though we may not be brothers, we are all hundredth cousins.”