Letters to Nature
Nature 431, 562-566 (30 September 2004) | doi:10.1038/nature02842; Received 30 December 2003; Accepted 14 July 2004
Correspondence to: Douglas L. T. Rohde1
Partial Abstract:
If a common ancestor of all living humans is defined as an individual who is a genealogical ancestor of all present-day people, the most recent common ancestor (MRCA) for a randomly mating population would have lived in the very recent past1,2,3. However, the random mating model ignores essential aspects of population substructure, such as the tendency of individuals to choose mates from the same social group, and the relative isolation of geographically separated groups. Here we show that recent common ancestors also emerge from two models incorporating substantial population substructure. One model, designed for simplicity and theoretical insight, yields explicit mathematical results through a probabilistic analysis. A more elaborate second model, designed to capture historical population dynamics in a more realistic way, is analysed computationally through Monte Carlo simulations. These analyses suggest that the genealogies of all living humans overlap in remarkable ways in the recent past. In particular, the MRCA of all present-day humans lived just a few thousand years ago in these models. Moreover, among all individuals living more than just a few thousand years earlier than the MRCA, each present-day human has exactly the same set of genealogical ancestors.
Yale News: "Most Recent Common Ancestor" of All Living Humans Surprisingly Recent
FOUND IN: Science & Engineering (Published: September 29, 2004)
New Haven, Conn. — In this week's issue of Nature, a Yale mathematician presents models showing that the most recent person who was a direct ancestor of all humans currently alive may have lived just a few thousand years ago.
"While we may not all be 'brothers,' the models suggest we are all hundredth cousins or so," said Joseph T. Chang, professor in the Department of Statistics at Yale University and senior author on the paper.
Chang established the basis of this research in a previous publication with an intentionally simplified model that ignored such complexities as geography and migration. Those precise mathematical results showed that in a world obeying the simplified assumptions, the most recent common ancestor would have lived less than 1,000 years ago. He also introduced the "identical ancestors point," the most recent time -- less than 2,000 years ago in the simplified model -- when each person was an ancestor to all or ancestor to none of the people alive today.
The current paper presents more realistic mathematical and computer models. It incorporates factors such as socially driven mating, physical barriers of geography and migration, and recorded historical events. Although such complexities make pure mathematical analysis difficult, it was possible to integrate them into an elaborate computer simulation model. The computer repeatedly simulated history under varying assumptions, tracking the lives, movements, and reproduction of all people who lived within the last 20,000 years.
These more realistic models estimate that the most recent common ancestor of mankind lived as recently as about 3,000 years ago, and the identical ancestors point was as recent as several thousand years ago. The paper suggests, "No matter the languages we speak or the color of our skin, we share ancestors who planted rice on the banks of the Yangtze, who first domesticated horses on the steppes of the Ukraine, who hunted giant sloths in the forests of North and South America, and who labored to build the Great Pyramid of Khufu."
The results can also work backwards, into the future. According to Chang, "Within two thousand years, it is likely that everyone on earth will be descended from most of us."
Other authors are Douglas L.T. Rhode of the Massachusetts Institute of Technology and Steve Olson of Bethesda, MD. The National Institutes of Health supported this research.
Citation: Nature, 431, 562- 565, (September 30, 2004). For solicited commentary on this paper, see News & Views and supplementary material in the same issue.
